{"id":510,"date":"2026-08-27T08:03:56","date_gmt":"2026-08-27T15:03:56","guid":{"rendered":"https:\/\/www.ultalabtests.com\/blog\/?p=510"},"modified":"2026-08-27T08:52:15","modified_gmt":"2026-08-27T15:52:15","slug":"the-a1c-test-compared-to-the-15-ag-test-which-is-best-for-you","status":"publish","type":"post","link":"https:\/\/www.ultalabtests.com\/blog\/diabetes\/diabetes-health\/the-a1c-test-compared-to-the-15-ag-test-which-is-best-for-you\/","title":{"rendered":"1,5-Anhydroglucitol (1,5-AG): When A1C May Miss Recent Glucose Spikes"},"content":{"rendered":"\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-anhydroglucitol-a1c-recent-glucose-spikes-hero-Large.jpeg?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"Red blood cells and a smooth A1C curve over 2\u20133 months beside a blood sample, kidney, and recent glucose peaks associated with 1,5-AG.\" class=\"wp-image-3821\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-anhydroglucitol-a1c-recent-glucose-spikes-hero-Large.jpeg?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-anhydroglucitol-a1c-recent-glucose-spikes-hero-Large.jpeg?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-anhydroglucitol-a1c-recent-glucose-spikes-hero-Large.jpeg?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-anhydroglucitol-a1c-recent-glucose-spikes-hero-Large.jpeg?w=1280&amp;quality=100&amp;ssl=1 1280w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">A1C estimates longer-term glucose exposure, while 1,5-AG can add shorter-term context about recent glycemic excursions. The results provide complementary\u2014not interchangeable\u2014information.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A1C and 1,5-anhydroglucitol do not compete for the same job.<\/strong> <a href=\"https:\/\/www.ultalabtests.com\/test\/hemoglobin-a1c-hgba1c\">A1C<\/a> is an established test for diabetes screening, diagnosis, and longer-term monitoring. <a href=\"https:\/\/www.ultalabtests.com\/test\/1-5-anhydroglucitol-intermediate-glycemic-control-test\">1,5-anhydroglucitol (1,5-AG)<\/a> is a narrower adjunctive marker that may fall when glucose has recently exceeded the kidney\u2019s reabsorption threshold and spilled into urine.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In selected people, a low 1,5-AG result may add context when A1C appears acceptable or unchanged but recent high-glucose excursions\u2014often after meals\u2014are still suspected. It is <strong>not<\/strong> an accepted stand-alone test for diagnosing diabetes, and it becomes unreliable for glycemic monitoring in people taking an SGLT2 inhibitor.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For the full diagnostic framework, see <a href=\"https:\/\/www.ultalabtests.com\/blog\/diabetes\/diabetes-prediabetes-blood-tests\/\">Diabetes and Prediabetes Blood Tests<\/a> and <a href=\"https:\/\/www.ultalabtests.com\/blog\/diabetes\/all-diabetes\/prediabetes-type-2-diabetes-tests\/\">Prediabetes and Type 2 Diabetes: Why A1C, Fasting Glucose, OGTT, Kidney, and Lipid Testing Must Be Read Together<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Key Takeaways<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-a1c-recent-glucose-spikes-hero.webp?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"A1C and 1,5-AG comparison showing A1C as a two-to-three-month average and 1,5-AG as a shorter-term marker of recent glucose excursions.\" class=\"wp-image-3819\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-a1c-recent-glucose-spikes-hero.webp?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-a1c-recent-glucose-spikes-hero.webp?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-a1c-recent-glucose-spikes-hero.webp?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-a1c-recent-glucose-spikes-hero.webp?resize=1536%2C864&amp;quality=100&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-a1c-recent-glucose-spikes-hero.webp?w=1600&amp;quality=100&amp;ssl=1 1600w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">A1C summarizes longer-term glucose exposure, while 1,5-AG may add context about more recent glycosuria-producing glucose excursions. The markers are not interchangeable.<\/figcaption><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>A1C estimates average glucose exposure over roughly two to three months and is an established diagnostic and monitoring test.<\/li>\n\n\n\n<li>1,5-AG is a circulating glucose-like molecule that is normally filtered and almost completely reabsorbed by the kidneys.<\/li>\n\n\n\n<li>When enough glucose enters urine, glucose competes with 1,5-AG for renal reabsorption; blood 1,5-AG falls.<\/li>\n\n\n\n<li>A lower 1,5-AG result can suggest more recent hyperglycemic excursions over approximately the preceding days to two weeks, but it does not show the timing, duration, or exact glucose value of each excursion.<\/li>\n\n\n\n<li>1,5-AG is most plausibly useful as an adjunct when A1C is near an individualized goal or appears stable but recent glucose spikes remain a specific question.<\/li>\n\n\n\n<li>Continuous glucose monitoring or structured home glucose measurements usually show excursions more directly.<\/li>\n\n\n\n<li>SGLT2 inhibitors intentionally increase urinary glucose and make 1,5-AG unreliable for glycemic monitoring; FDA labeling recommends an alternative method.<a href=\"#ref-1\">[1]<\/a><\/li>\n\n\n\n<li>Kidney and tubular function, pregnancy, assay-specific reference intervals, diet, population differences, and persistent severe hyperglycemia can limit interpretation.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Why the Old \u201cWhich Test Is Best?\u201d Question Was Misleading<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The original article compared A1C with 1,5-AG as though a reader needed to choose one winner. That framing created two problems:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>It placed an established diagnostic test and a specialized adjunctive marker on equal footing.<\/li>\n\n\n\n<li>It did not adequately separate <strong>average glucose exposure<\/strong> from <strong>recent renal glucose-spillover signals<\/strong>.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">The better question is:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>When might 1,5-AG provide information about recent glucose excursions that A1C does not show?<\/strong><\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">The answer depends on the clinical question, medications, kidney function, and whether more direct glucose data are available.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What A1C Measures<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><a href=\"https:\/\/www.ultalabtests.com\/test\/hemoglobin-a1c-hgba1c\">Hemoglobin A1C<\/a> measures the percentage of hemoglobin with glucose attached. Because red blood cells circulate for weeks to months, A1C estimates longer-term average glucose exposure, with greater influence from more recent weeks.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A1C is widely used because it is standardized, convenient, and linked to established diagnostic criteria. It does not require fasting. However, an average cannot show every high and low. Two people can have the same A1C but very different day-to-day patterns.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A1C may be less representative when red-cell turnover or hemoglobin biology changes. Important examples include iron or B12 deficiency, hemolysis, recent blood loss or transfusion, kidney failure, pregnancy, erythropoietin treatment, and some hemoglobin variants.<a href=\"#ref-2\">[2]<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When A1C does not match direct glucose data, the discrepancy should be investigated rather than \u201ccorrected\u201d by assuming either test is automatically right.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What 1,5-AG Measures<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">1,5-AG is a naturally occurring monosaccharide found in blood. It is filtered by the kidneys and usually reabsorbed in the renal tubules. When plasma glucose becomes high enough to produce glycosuria, glucose interferes with 1,5-AG reabsorption. More 1,5-AG is lost in urine, and its blood concentration falls.<a href=\"#ref-3\">[3]<\/a><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/how-1-5-ag-works-kidney-glucose-spillover.webp?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"Kidney pathway showing filtration and reabsorption of 1,5-AG and how urinary glucose spillover causes more 1,5-AG to be lost in urine.\" class=\"wp-image-3813\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/how-1-5-ag-works-kidney-glucose-spillover.webp?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/how-1-5-ag-works-kidney-glucose-spillover.webp?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/how-1-5-ag-works-kidney-glucose-spillover.webp?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/how-1-5-ag-works-kidney-glucose-spillover.webp?resize=1536%2C864&amp;quality=100&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/how-1-5-ag-works-kidney-glucose-spillover.webp?w=1600&amp;quality=100&amp;ssl=1 1600w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">When glucose spills into urine, it interferes with renal reabsorption of 1,5-AG. More 1,5-AG is lost in urine, causing its blood concentration to fall.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">This mechanism creates an inverse relationship:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Higher 1,5-AG<\/strong> generally suggests less recent glucose spillover into urine.<\/li>\n\n\n\n<li><strong>Lower 1,5-AG<\/strong> may suggest more recent periods of substantial hyperglycemia.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The marker responds over a shorter interval than A1C\u2014often described as approximately several days to two weeks. It is especially sensitive to glucose excursions that cross the renal threshold, but the exact threshold varies among people and circumstances.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">1,5-AG does not identify exactly when a spike occurred, how high it rose, how long it lasted, whether hypoglycemia also occurred, or which meal or medication caused the pattern.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">A1C and 1,5-AG Side by Side<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-vs-1-5-ag-glycemic-time-window.webp?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"Timeline comparing the two-to-three-month glycemic window of A1C with the shorter recent-excursion window represented by 1,5-AG.\" class=\"wp-image-3814\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-vs-1-5-ag-glycemic-time-window.webp?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-vs-1-5-ag-glycemic-time-window.webp?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-vs-1-5-ag-glycemic-time-window.webp?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-vs-1-5-ag-glycemic-time-window.webp?resize=1536%2C864&amp;quality=100&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-vs-1-5-ag-glycemic-time-window.webp?w=1600&amp;quality=100&amp;ssl=1 1600w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">A1C reflects longer-term average glucose exposure, whereas 1,5-AG responds over a shorter interval to recent glucose spillover into urine. Neither marker displays the exact timing of individual spikes.<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Feature<\/th><th>A1C<\/th><th>1,5-AG<\/th><\/tr><\/thead><tbody><tr><td>Primary role<\/td><td>Established screening, diagnosis, and longer-term monitoring<\/td><td>Selected adjunct for recent hyperglycemic excursions<\/td><\/tr><tr><td>Approximate window<\/td><td>About two to three months<\/td><td>Recent days to roughly two weeks<\/td><\/tr><tr><td>Direction with hyperglycemia<\/td><td>Usually rises<\/td><td>Usually falls<\/td><\/tr><tr><td>Main biological basis<\/td><td>Glucose attachment to hemoglobin<\/td><td>Renal loss when glycosuria interferes with tubular reabsorption<\/td><\/tr><tr><td>Shows exact spikes?<\/td><td>No<\/td><td>No<\/td><\/tr><tr><td>Used to diagnose diabetes?<\/td><td>Yes, with standardized methods and confirmation rules<\/td><td>No\u2014do not use as a stand-alone diagnostic test<\/td><\/tr><tr><td>Major limitations<\/td><td>Red-cell turnover, hemoglobin variants, kidney failure, pregnancy, recent transfusion, and other factors<\/td><td>SGLT2 inhibitors, altered renal glucose handling, kidney\/tubular disease, pregnancy, variable thresholds and reference intervals<\/td><\/tr><tr><td>Best interpreted with<\/td><td>Plasma glucose, clinical context, and glucose monitoring when needed<\/td><td>A1C, plasma glucose, medication list, kidney function, and direct glucose data<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">When 1,5-AG May Add Useful Context<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/when-1-5-ag-testing-may-help-decision-tree.webp?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"Decision guide for considering 1,5-AG when A1C is stable but recent glucose excursions are suspected, with direct glucose monitoring as an alternative.\" class=\"wp-image-3810\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/when-1-5-ag-testing-may-help-decision-tree.webp?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/when-1-5-ag-testing-may-help-decision-tree.webp?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/when-1-5-ag-testing-may-help-decision-tree.webp?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/when-1-5-ag-testing-may-help-decision-tree.webp?resize=1536%2C864&amp;quality=100&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/when-1-5-ag-testing-may-help-decision-tree.webp?w=1600&amp;quality=100&amp;ssl=1 1600w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">1,5-AG may add context when A1C appears stable but recent substantial glucose excursions remain a defined question. It is an adjunct and does not replace A1C or direct glucose monitoring.<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">1,5-AG may be considered when all of the following are true:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The person has known diabetes or a clinician-defined monitoring question.<\/li>\n\n\n\n<li>A1C is near an individualized goal, stable, or otherwise not explaining suspected recent hyperglycemia.<\/li>\n\n\n\n<li>Recent post-meal or episodic glucose excursions are specifically suspected.<\/li>\n\n\n\n<li>The person is <strong>not<\/strong> taking an SGLT2 inhibitor.<\/li>\n\n\n\n<li>Kidney function and renal glucose handling do not make the result uninterpretable.<\/li>\n\n\n\n<li>Continuous glucose monitoring or structured home testing is unavailable, incomplete, or being compared with a laboratory adjunct.<\/li>\n\n\n\n<li>A qualified healthcare professional can determine whether the result would change the monitoring plan.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Examples include an A1C that changes little despite high post-meal finger-stick readings, or a clinical concern that recent medication or nutrition changes produced short-term highs not yet reflected fully in A1C.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Even in these situations, 1,5-AG is an adjunct. It should not independently trigger medication changes.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">When 1,5-AG Is Usually the Wrong Tool<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-limitations-sglt2-kidney-pregnancy.webp?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"Major limitations of 1,5-AG testing, including SGLT2 inhibitor use, kidney or tubular dysfunction, pregnancy, and its inability to diagnose diabetes.\" class=\"wp-image-3818\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-limitations-sglt2-kidney-pregnancy.webp?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-limitations-sglt2-kidney-pregnancy.webp?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-limitations-sglt2-kidney-pregnancy.webp?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-limitations-sglt2-kidney-pregnancy.webp?resize=1536%2C864&amp;quality=100&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-ag-limitations-sglt2-kidney-pregnancy.webp?w=1600&amp;quality=100&amp;ssl=1 1600w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">SGLT2 inhibitors, altered kidney physiology, pregnancy, and other clinical factors can limit 1,5-AG interpretation. The test is not used as a stand-alone diagnostic test for diabetes.<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Diagnosing prediabetes or diabetes<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Use standardized <a href=\"https:\/\/www.ultalabtests.com\/test\/hemoglobin-a1c-hgba1c\">A1C<\/a>, <a href=\"https:\/\/www.ultalabtests.com\/test\/glucose\">fasting plasma glucose<\/a>, or <a href=\"https:\/\/www.ultalabtests.com\/test\/glucose-tolerance-test-2-specimens-75g\">two-hour 75-g OGTT<\/a> criteria. 1,5-AG is not a substitute.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Taking an SGLT2 inhibitor<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">SGLT2 inhibitors lower glucose partly by increasing urinary glucose excretion. That mechanism lowers 1,5-AG independently of the glycemic question the test is supposed to answer. Current FDA labeling states that 1,5-AG measurements are unreliable for assessing glycemic control in people taking SGLT2 inhibitors and recommends alternative methods.<a href=\"#ref-1\">[1]<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Common medications in this class include agents containing empagliflozin, dapagliflozin, canagliflozin, ertugliflozin, and bexagliflozin. Medication lists and combination products should be reviewed carefully.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Significant kidney or tubular dysfunction<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Because the test depends on filtration and tubular reabsorption, altered kidney physiology can change 1,5-AG independently of recent glucose excursions. Interpretation should include creatinine\/eGFR, albuminuria, and the clinical kidney history when relevant.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Pregnancy<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Pregnancy changes renal glucose handling and uses specialized diabetes screening and monitoring protocols. 1,5-AG should not replace established pregnancy-specific testing or obstetric care.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Persistent, clearly uncontrolled hyperglycemia<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">When glucose is repeatedly high and A1C is already markedly elevated, the key problem is not hidden excursions. 1,5-AG may be very low and provide little additional actionable discrimination.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Suspected hypoglycemia<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A low 1,5-AG reflects recent high-glucose exposure through its renal mechanism; it does not measure low glucose. Use direct glucose monitoring for hypoglycemia.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">A More Direct Way to See Excursions<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Continuous glucose monitoring (CGM) and structured home glucose testing can show the timing, peak, duration, and frequency of glucose changes. They can also reveal hypoglycemia, which 1,5-AG cannot.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Laboratory markers still have value:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>A1C summarizes longer-term exposure.<\/li>\n\n\n\n<li>Fructosamine or glycated albumin may reflect a shorter protein-glycation interval in selected circumstances.<\/li>\n\n\n\n<li>1,5-AG may reflect recent glycosuria-producing highs.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">But none of these laboratory markers recreates a glucose trace. When the clinical question is \u201cWhat happens after breakfast?\u201d a timed glucose measurement or CGM is often more direct than an indirect biomarker.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How to Interpret a 1,5-AG Result<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Use the laboratory\u2019s assay-specific reference interval. Do not apply a universal cutoff copied from a study population or another assay.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A practical interpretation sequence is:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Confirm the medication list.<\/strong> Exclude SGLT2 inhibitor use.<\/li>\n\n\n\n<li><strong>Define the question.<\/strong> Is the concern recent highs that A1C may average away?<\/li>\n\n\n\n<li><strong>Review kidney context.<\/strong> Consider eGFR, UACR, tubular disease, pregnancy, and other factors affecting glycosuria.<\/li>\n\n\n\n<li><strong>Compare with A1C and direct glucose.<\/strong> A low 1,5-AG is not meaningful in isolation.<\/li>\n\n\n\n<li><strong>Look at trends when appropriate.<\/strong> A change over time may be more informative than one value, provided the same assay and comparable conditions are used.<\/li>\n\n\n\n<li><strong>Do not infer treatment from the result alone.<\/strong> Medication and insulin changes require clinician oversight.<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\">Common Result Combinations<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"576\" src=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-1-5-ag-common-result-patterns.webp?resize=1024%2C576&#038;quality=100&#038;ssl=1\" alt=\"Five educational A1C and 1,5-AG result patterns showing how longer-term average glucose and recent-excursion signals may align or disagree.\" class=\"wp-image-3817\" srcset=\"https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-1-5-ag-common-result-patterns.webp?resize=1024%2C576&amp;quality=100&amp;ssl=1 1024w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-1-5-ag-common-result-patterns.webp?resize=300%2C169&amp;quality=100&amp;ssl=1 300w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-1-5-ag-common-result-patterns.webp?resize=768%2C432&amp;quality=100&amp;ssl=1 768w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-1-5-ag-common-result-patterns.webp?resize=1536%2C864&amp;quality=100&amp;ssl=1 1536w, https:\/\/i0.wp.com\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/a1c-1-5-ag-common-result-patterns.webp?w=1600&amp;quality=100&amp;ssl=1 1600w\" sizes=\"auto, (max-width: 1000px) 100vw, 1000px\" \/><figcaption class=\"wp-element-caption\">Different A1C and 1,5-AG combinations may suggest different monitoring questions, but the pattern is not a diagnosis. Medications, kidney function, red-cell factors, and direct glucose data remain essential.<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Pattern<\/th><th>Possible meaning<\/th><th>What to check next<\/th><\/tr><\/thead><tbody><tr><td>A1C near goal + low 1,5-AG<\/td><td>Recent substantial glucose excursions may be occurring despite an acceptable average.<\/td><td>Review CGM or timed post-meal glucose, medications, kidney function, and diet\/activity context.<\/td><\/tr><tr><td>A1C high + low 1,5-AG<\/td><td>Persistent hyperglycemia is already evident; 1,5-AG may add little.<\/td><td>Prioritize direct glucose assessment and clinical management.<\/td><\/tr><tr><td>A1C high + relatively preserved 1,5-AG<\/td><td>Results may reflect different windows, an A1C influence, or assay\/renal factors.<\/td><td>Confirm A1C, plasma glucose, CBC\/iron\/B12 or hemoglobin context when indicated.<\/td><\/tr><tr><td>A1C near goal + preserved 1,5-AG<\/td><td>No strong 1,5-AG signal of recent glycosuria-producing excursions.<\/td><td>This does not exclude smaller spikes, lows, or variability below the renal threshold.<\/td><\/tr><tr><td>Any A1C + low 1,5-AG while taking an SGLT2 inhibitor<\/td><td>Expected drug-related interference is likely.<\/td><td>Do not use 1,5-AG to assess glycemic control; use alternative monitoring.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Related Ulta Lab Tests<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Test<\/th><th>Best use in this question<\/th><th>Key limitation<\/th><\/tr><\/thead><tbody><tr><td><a href=\"https:\/\/www.ultalabtests.com\/test\/1-5-anhydroglucitol-intermediate-glycemic-control-test\">1,5-Anhydroglucitol (1,5-AG)<\/a><\/td><td>Selected adjunct for recent glycosuria-producing hyperglycemic excursions<\/td><td>Not diagnostic; unreliable with SGLT2 inhibitors and affected by renal physiology.<\/td><\/tr><tr><td><a href=\"https:\/\/www.ultalabtests.com\/test\/hemoglobin-a1c-hgba1c\">Hemoglobin A1C<\/a><\/td><td>Established longer-term glycemic exposure and diagnostic criterion<\/td><td>Can hide variability and be distorted by red-cell factors.<\/td><\/tr><tr><td><a href=\"https:\/\/www.ultalabtests.com\/test\/glucose\">Glucose<\/a><\/td><td>Direct glucose concentration at collection<\/td><td>One moment; preparation and timing matter.<\/td><\/tr><tr><td><a href=\"https:\/\/www.ultalabtests.com\/test\/glucose-tolerance-test-2-specimens-75g\">Two-hour 75-g OGTT<\/a><\/td><td>Standardized detection of post-challenge dysglycemia<\/td><td>Longer visit; does not provide day-to-day monitoring.<\/td><\/tr><tr><td><a href=\"https:\/\/www.ultalabtests.com\/test\/comprehensive-metabolic-panel-test-cmp\">Comprehensive Metabolic Panel<\/a><\/td><td>Glucose, creatinine\/eGFR, electrolytes, and related context<\/td><td>Does not replace UACR or direct glucose pattern data.<\/td><\/tr><tr><td><a href=\"https:\/\/www.ultalabtests.com\/test\/albumin-random-urine-test-with-creatinine\">Urine Albumin\/Creatinine Ratio<\/a><\/td><td>Kidney-damage context in diabetes<\/td><td>Temporary elevations occur; not a measure of glucose excursions.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Frequently Asked Questions<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Is 1,5-AG better than A1C?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. A1C has an established role in diagnosis and long-term monitoring. 1,5-AG has a narrower adjunctive role for selected recent hyperglycemia questions.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does low 1,5-AG mean my glucose spiked after meals?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">It may indicate recent glucose high enough to increase urinary glucose, but it cannot prove that the excursions occurred after meals or show their timing. Direct glucose data are needed for that level of detail.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Can 1,5-AG replace a continuous glucose monitor?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. CGM shows glucose over time, including highs, lows, timing, and duration. 1,5-AG is an indirect summary influenced by renal glucose handling.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">How quickly can 1,5-AG change?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">It can respond over days as urinary glucose exposure changes, with common descriptions covering approximately several days to two weeks. The rate varies and should not be used as a precise clock.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Should I order 1,5-AG if I take an SGLT2 inhibitor?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Not to monitor glycemic control. FDA prescribing information states that measurements are unreliable in this setting and recommends alternative methods.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Can a normal 1,5-AG rule out glucose variability?<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">No. Smaller spikes below the renal threshold, hypoglycemia, and rapid fluctuations may not lower 1,5-AG meaningfully.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How Ulta Lab Tests Helps<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Ulta Lab Tests provides direct access to many laboratory tests where available. Before ordering, review the <a href=\"https:\/\/www.ultalabtests.com\/blog\/lab-testing-knowledge-center\/complete-guide-to-lab-tests-and-blood-work\/\">Complete Guide to Lab Tests and Blood Work<\/a>, <a href=\"https:\/\/www.ultalabtests.com\/blog\/lab-testing-knowledge-center\/how-to-read-lab-results\/\">How to Read and Understand Your Lab Results<\/a>, and <a href=\"https:\/\/www.ultalabtests.com\/blog\/lab-testing-knowledge-center\/direct-access-lab-testing\/\">Direct-Access Lab Testing: A Complete Guide<\/a>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Testing should answer a defined question. A specialized marker is not automatically more informative than an established test or direct glucose data.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Summary<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">A1C and 1,5-AG measure different biological signals. A1C is the established longer-term marker. 1,5-AG may add short-term context when recent glycosuria-producing glucose excursions are suspected and A1C does not reveal them. Its value is limited by medication and kidney physiology\u2014especially SGLT2 inhibitor use\u2014and it should never replace standard diagnostic criteria, CGM, home glucose data, or clinical judgment.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">References<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>U.S. Food and Drug Administration. <a href=\"https:\/\/www.accessdata.fda.gov\/drugsatfda_docs\/label\/2026\/209803s012lbl.pdf\">STEGLATRO prescribing information\u2014interference with the 1,5-AG assay<\/a>. 2026.<\/li>\n\n\n\n<li>Sacks DB, et al. <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC10516260\/\">Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus<\/a>. <em>Clinical Chemistry<\/em>. 2023.<\/li>\n\n\n\n<li>Xu H, et al. <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC11560458\/\">The Clinical Potential of 1,5-Anhydroglucitol as a Biomarker in Diabetes Mellitus<\/a>. 2024.<\/li>\n\n\n\n<li>American Diabetes Association Professional Practice Committee. <a href=\"https:\/\/diabetesjournals.org\/care\/article\/49\/Supplement_1\/S27\/163926\/2-Diagnosis-and-Classification-of-Diabetes\">Diagnosis and Classification of Diabetes: Standards of Care in Diabetes\u20142026<\/a>. <em>Diabetes Care<\/em>. 2026.<\/li>\n\n\n\n<li>Selvin E, et al. <a href=\"https:\/\/diabetesjournals.org\/care\/article\/48\/8\/1446\/160593\/Detecting-Hyperglycemia-Using-Biomarkers-Versus\">Detecting Hyperglycemia Using Biomarkers Versus Continuous Glucose Monitoring<\/a>. <em>Diabetes Care<\/em>. 2025.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\"><p style=\"margin: 0px; font-style: normal; font-variant-caps: normal; font-width: normal; font-size: 13px; line-height: normal; font-family: &quot;Helvetica Neue&quot;; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-variant-emoji: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal;\"><b>Originally published:<\/b> October 9, 2023 | <b>Substantively updated:<\/b> August 27 2026<\/p><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Editorial disclaimer: This article is educational and does not establish a diagnosis or treatment plan. Medication changes and glucose-management decisions require qualified clinical guidance<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A1C and 1,5-anhydroglucitol do not compete for the same job. A1C is an established test for diabetes screening, diagnosis, and longer-term monitoring. 1,5-anhydroglucitol (1,5-AG) is a narrower adjunctive marker that may fall when glucose has [&hellip;]<\/p>\n","protected":false},"author":5,"featured_media":3822,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":true,"om_disable_all_campaigns":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[82,81,87,88,83,89],"tags":[4598,5772,5770,491,5773,5769,5771,5774,5768],"class_list":["post-510","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blood-sugar","category-diabetes","category-all-diabetes","category-diabetes-health","category-diabetes-management","category-diabetes-screening","tag-4598","tag-5-ag","tag-5-anhydroglucitol","tag-a1c","tag-glucose-spikes","tag-glycemic-markers","tag-post-meal-glucose","tag-recent-glucose-excursions","tag-sglt2-inhibitors"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.3 (Yoast SEO v28.4) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>1,5-Anhydroglucitol (1,5-AG): When A1C May Miss Recent Glucose Spikes | Ulta Lab Tests<\/title>\n<meta name=\"description\" content=\"The 1,5-AG test can add context when A1C misses glucose spikes. Learn when recent glucose excursions matter, and when this marker is limited.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ultalabtests.com\/blog\/diabetes\/diabetes-health\/the-a1c-test-compared-to-the-15-ag-test-which-is-best-for-you\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"1,5-Anhydroglucitol (1,5-AG): When A1C May Miss Recent Glucose Spikes\" \/>\n<meta property=\"og:description\" content=\"The 1,5-AG test can add context when A1C misses glucose spikes. Learn when recent glucose excursions matter, and when this marker is limited.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ultalabtests.com\/blog\/diabetes\/diabetes-health\/the-a1c-test-compared-to-the-15-ag-test-which-is-best-for-you\/\" \/>\n<meta property=\"og:site_name\" content=\"Ulta Lab Tests\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/facebook.com\/ultalabtests\" \/>\n<meta property=\"article:published_time\" content=\"2026-08-27T15:03:56+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-08-27T15:52:15+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.ultalabtests.com\/blog\/wp-content\/uploads\/2026\/08\/1-5-anhydroglucitol-a1c-recent-glucose-spikes-social-square-Large.jpeg\" \/>\n\t<meta property=\"og:image:width\" content=\"1254\" \/>\n\t<meta property=\"og:image:height\" content=\"1254\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"John R\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"John R\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"12 minutes\" \/>\n<!-- \/ Yoast SEO Premium plugin. -->","yoast_head_json":{"title":"1,5-Anhydroglucitol (1,5-AG): When A1C May Miss Recent Glucose Spikes | Ulta Lab Tests","description":"The 1,5-AG test can add context when A1C misses glucose spikes. 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