Lactose Intolerance

Lactose intolerance happens when the small intestine doesn’t make enough lactase, the enzyme that breaks down lactose (the sugar in milk). Undigested lactose is fermented by gut bacteria, causing bloating, gas, cramping, and diarrhea. A proactive testing plan starts with breath testing while you’re on a lactose challenge; in infants and toddlers, stool acidityhelps identify carbohydrate malabsorption. Genetic testing can show a tendency toward adult lactase non-persistence, and rule-out labs check for conditions that can mimic or worsen symptoms (e.g., celiac diseaseIBD).

Lab results help confirm lactose malabsorption, distinguish it from other causes, and set a baseline for future decisions. Testing does not replace a clinician’s exam, dietary review, or endoscopy when alarm features are present.

Signs, Symptoms & Related Situations

  • Typical after dairy: bloating, abdominal cramping, gas, watery stools, urgency

  • Timing: symptoms begin 30 minutes to a few hours after lactose intake

  • Infants/toddlers: acidic, watery stools; diaper rash; poor weight gain if intake continues

  • Secondary causes: recent gastroenteritis, celiac disease, IBD, SIBO, and some medications can reduce lactase temporarily

  • Not lactose intolerance: immediate hives, wheeze, or anaphylaxis suggest milk allergy (IgE-mediated), not enzyme deficiency

  • When to seek urgent care: persistent bloody or black stools, severe dehydration, high fever, rapid weight loss, or severe abdominal pain
    All symptoms should be evaluated by a qualified clinician.

Why These Tests Matter

What testing can do

  • Demonstrate malabsorption with objective breath hydrogen/methane responses after a lactose load

  • Support diagnosis in infants with stool acidity/reducing substances

  • Identify genetic risk for adult lactase non-persistence (LCT variant)

  • Rule out mimics (celiac disease, IBD) that need different management

What testing cannot do

  • Prove milk protein allergy (a different condition requiring IgE testing and clinical evaluation)

  • Determine the exact amount of lactose you can tolerate—results must be paired with clinical guidance

  • Replace endoscopy or imaging when alarm features are present

What These Tests Measure (at a glance)

  • Lactose Hydrogen/Methane Breath Test: measures hydrogen (H2) and methane (CH4) in breath after a standard lactose drink. A rise in H2 ≥20 ppm (or CH4 ≥10 ppm) over baseline within the test window supports lactose malabsorptionCaveat: antibiotics, probiotics, recent colon prep, smoking, vigorous exercise, and high-fiber foods can affect results—follow prep carefully. Early peaks can suggest SIBO.

  • Stool Acidity (infants/toddlers): low stool pH (typically <5.5) and reducing substances indicate carbohydrate malabsorption. Caveat: nonspecific; interpret with diet and growth history.

  • LCT Genotyping (e.g., −13910 C/T upstream of LCT): identifies adult lactase non-persistence risk (CC genotype) vs persistence (CT/TT). Caveat: does not detect secondary lactose intolerance from mucosal injury (e.g., celiac, infection).

  • Rule-out Panels (as indicated):

    • Celiac serology: tTG-IgA with total IgA (reflex to IgG tests if IgA deficient)

    • Fecal calprotectin/lactoferrin: screens for IBD-type inflammation

    • GI pathogen testing: selective use with acute infectious features

    • CBC/CMP: anemia, electrolytes, protein status (impact context)

How the Testing Process Works

  1. Choose the starting test: most older children/adults begin with a hydrogen/methane breath test; infants often use stool acidity/reducing substances.

  2. Prepare correctly: follow the pre-test diet and medication hold (e.g., fasting, avoid antibiotics/probiotics per instructions, no smoking/exercise just before the test).

  3. Collect samples: serial breath samples after the lactose drink (or stool sample for infants).

  4. Get results securely: most reports post within a few days.

  5. Follow up with your clinician: combine results with symptoms and, if indicated, rule-out testing (celiac panel, fecal calprotectin). Plan next steps.

Interpreting Results (General Guidance)

  • Breath test positive (rise in H2/CH4): supports lactose malabsorption; magnitude and timing help context (very early rise may suggest SIBO).

  • Breath test negative with classic symptoms: consider non-hydrogen or methane producers, prep issues, low test dose, or alternate diagnoses—your clinician may repeat testing or consider genotype/rule-outs.

  • Infant stool acidity positive: supports carbohydrate malabsorption; correlate with feeding history and growth.

  • Genotype consistent with non-persistence: aligns with adult-type hypolactasia; does not rule out additional causes of symptoms.
    Always interpret results with a qualified healthcare professional.

Choosing Panels vs. Individual Tests

  • First-line (teens/adults): Hydrogen/Methane Lactose Breath Test

  • Infants/toddlers: Stool acidity (± reducing substances)

  • Persistent or atypical symptoms: add LCT genotype and rule-out panels (tTG-IgA/total IgA; fecal calprotectin)

  • Suspected SIBO or very early breath rise: consider lactulose breath test (clinician-directed) and targeted stool/blood tests

  • Impact context: CBC/CMP for anemia/electrolytes if symptoms are chronic or severe

FAQs

Is lactose intolerance the same as milk allergy?
No. Lactose intolerance is an enzyme deficiency; milk allergy is an immune (IgE) reaction with different testing and risks.

Do I need to be off antibiotics before breath testing?
Usually yes. Recent antibiotics, probiotics, or colon preps can alter results—follow the prep instructions provided with your test.

Can breath tests be false-negative?
Yes. Some people produce little hydrogen; measuring methane improves detection. Prep errors can also affect results.

What if my symptoms started after a stomach bug?
That can be secondary lactose intolerance—often temporary. Testing can document malabsorption while rule-out labs check for other causes.

Does genetic testing replace breath testing?
No. Genotyping shows risk for adult non-persistence; breath testing documents current malabsorption.

Should I stop dairy before testing?
Most tests require specific prep but not eliminating lactose beforehand; follow the instructions for accurate results.

Internal Links & Cross-References

  • Digestive System Tests Hub

  • Celiac Disease • Inflammatory Bowel Disease (IBD) • Irritable Bowel Syndrome (IBS) • Colon (Intestine) • Digestive Health

  • Key Lab Tests: Lactose Hydrogen/Methane Breath Test • Stool Acidity/Reducing Substances (Pediatric) • LCT Genotyping • tTG-IgA • Total IgA • Fecal Calprotectin • CBC • CMP

References

  1. World Gastroenterology Organisation (WGO). Global Guideline: Lactose Intolerance.

  2. North American Consensus on Hydrogen and Methane Breath Testing—Indications, Preparation, and Interpretation.

  3. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Lactose Intolerance—Testing and Diagnosis.

  4. American Academy of Pediatrics. Evaluation of Chronic Diarrhea and Carbohydrate Malabsorption in Infants and Children.

  5. American Gastroenterological Association (AGA). Clinical Practice Updates on Breath Testing and Carbohydrate Malabsorption.

  6. American College of Gastroenterology (ACG). Clinical Guideline for Small Intestinal Bacterial Overgrowth (context for early breath rises).

Available Tests & Panels

Your lactose intolerance test menu is pre-populated in the Ulta Lab Tests system. Start with a hydrogen/methane lactose breath test (older children/adults) or stool acidity (infants), add LCT genotyping or rule-out panels (celiac serology, fecal calprotectin) when needed, and review all results with your clinician.

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The Helicobacter pylori Urea Breath Test detects H. pylori infection, a common cause of ulcers and gastritis. After drinking a urea solution, breath samples are analyzed for carbon dioxide changes caused by the bacteria. A positive result indicates active infection, while a negative shows no evidence of H. pylori. Doctors use this noninvasive test to diagnose infection, confirm eradication after treatment, and monitor gastrointestinal health.

Varied
Phlebotomist
Also Known As: H Pylori Breath Test

The Reducing Substances Stool Test measures sugars in stool to assess carbohydrate digestion and absorption. Elevated levels can point to lactose intolerance, hereditary enzyme deficiencies, or gastrointestinal conditions affecting nutrient breakdown. By identifying unabsorbed carbohydrates, this test helps clinicians evaluate chronic diarrhea, bloating, abdominal discomfort, or pediatric feeding problems, offering valuable information about intestinal and metabolic health.

Stool
Stool Collection

The Milk f2 IgE Test measures IgE antibodies to proteins in cow’s milk. Elevated levels may indicate an allergic reaction, which can cause hives, itching, swelling, digestive issues, respiratory symptoms, or, in severe cases, anaphylaxis. This test helps identify milk allergies and supports management through dietary avoidance and treatment strategies guided by healthcare providers.

Blood
Blood Draw
Also Known As: Milk IgE Test, Milk f2 Test

The Milk Component Panel measures IgE antibodies to alpha-lactalbumin (F76), beta-lactoglobulin (F77), and casein (F78), the major milk proteins linked to allergic reactions. Elevated levels may confirm cow’s milk allergy, which can cause hives, digestive upset, or anaphylaxis. Doctors use this test to identify specific milk protein sensitivities, guide dietary restrictions, and support management of food allergies in children and adults.

Also Known As: Milk Allergy Panel, Milk Allergy Test

Blood
Blood Draw

7 Frequently Asked Questions About Lactose Intolerance Tests

Stomachaches, gas, loose stools - there are plenty of unfortunate consequences of lactose intolerance.

But how do you know if you're lactose intolerant? What if you're just prone to having stomach issues?

If you're experiencing chronic digestive discomfort, then you should consider lactose intolerance tests, especially if you feel pain after ingesting a lot of dairy.

Give yourself the best chance for comfort. Sometimes, taking a test can do just that.

So keep reading for seven frequently asked questions about lactose intolerance tests. Afterward, you'll be ready to change your lifestyle and diet for the better.

What is Lactose Intolerance?

Lactose intolerance refers to a body's inability to digest lactose, a natural sugar in dairy products. When a lactose-intolerant person ingests lactose, the lactose will move through the digestive system without proper digestion.

Is Lactose Intolerance an Allergy?

No. Allergies are defined by an immune system's misguided reaction to typically harmless substances. A severe allergic reaction can cause anaphylactic shock, which can turn lethal.

Instead, lactose intolerance can be extremely uncomfortable. But while it causes discomfort, it usually does not result in serious medical consequences.

Who is at Higher Risk for Lactose Intolerance?

The most defining factor for lactose intolerance is ethnicity. Those of Asian, Hispanic, African, and Native American descent are at higher risk of lactose intolerance than others.

Ethnic Group                % Of Lactose Intolerance in Adults 

  • Southeast Asians         98% 
  • Indian Adults                50% 
  • Asian Americans          90% 
  • African Americans      79% 
  • Mexican Americans     55% 
  • Northern Europeans   05% 

A less common factor is premature birth. That's because the small intestine typically develops cells that produce lactase late into the third trimester. But babies born before that period don't usually have the chance to develop enough of those cells.

However, these are only risk factors, not risk guarantees. It's possible for an individual to meet all these criteria but not have lactose intolerance. Also, people can meet none of these criteria and still develop lactose intolerance.

What Causes Lactose Intolerance?

The body's inability to digest lactose starts with the small intestine. Once again, the small intestine is responsible for developing cells that produce lactase. Lactase is necessary for breaking down lactose.

We've already covered demographics that are at higher risk for lactose intolerance. But lactose intolerance can also be inherited from a parent. For that reason, lactose intolerance very commonly runs in families.

But sometimes, people can experience brief periods of lactose intolerance without experiencing it chronically. That's because conditions like short-term illness, especially stomach illnesses, can cause the small intestine to stop developing lactase-producing cells.

However, long-term illnesses can also cause long-term lactose intolerance. In these cases, lactose intolerance typically lasts as long as the disease does. However, long-term conditions may persist for life.

What are the Symptoms of Lactose Intolerance?

The symptoms of lactose intolerance occur primarily due to undigested lactose reaching the large intestines. Extra fluids will be drawn into the large intestines, where bacteria break down the lactose. It will result in the excess production of hydrogen gas and lactic acid. This may cause: 

  • Bloating
  • Gas
  • Diarrhea
  • Nausea
  • Vomiting
  • Stomach cramps
  • Stomachaches

These symptoms appear quite quickly after lactose ingestion. For that reason, it can be easy to tell whether someone has lactose intolerance.

However, some people are less lactose intolerant than others and are comfortable ingesting a small amount of dairy and milk. Not only that but some milk and dairy products are naturally low in lactose. Butter, probiotic yogurt, and hard cheeses are all low in lactose. Many lactose-intolerant people can digest these products with no problem. There may be individuals that are extremely lactose intolerant, but these foods are generally safe for most lactose-intolerant people to consume.

The severity of symptoms will vary depending on the individual and the amount and type of dairy products ingested. Many people who suffer from the condition can successfully consume small amounts of dairy products with few or no symptoms. Some people confuse lactose intolerance with an allergy to cow's milk. Milk allergy happens due to a reaction by the immune system. The allergy is directed against a protein in the milk but not sugar. A person who has a milk allergy can suffer mild to severe symptoms and even life-threatening reactions within minutes to hours soon after consuming cow's milk. They can also experience hives and wheezing and the other symptoms associated with the allergy. Lactose intolerance affects more adults than children. On the contrary, milk allergies are much more common in young kids who tend to outgrow the allergy with aging.  

Types of Lactose Intolerance 

There are a number of other conditions and diseases that can cause a secondary form of lactose intolerance in addition to the natural intolerance associated with increasing age. Damage to the lining of the small intestines can lead to the inability to absorb lactose in a beneficial manner. Radiation therapy, celiac disease, inflammatory bowel disease (or IBS), chemotherapy, overgrowth of bacteria, or infections caused by parasites all may result in a decreased lactose digestion. Stomach contents in the small intestines move much quicker than normal in some people. These people can suffer from the condition because of insufficient time to digest lactose. Lactase deficiency is grouped into three clinical syndromes – alactasia (or congenital lactase deficiency), hypolactasia (or primary adult lactase deficiency), and secondary lactase deficiency. 

Congenital Lactase Deficiency 

There are two genes linked to the production of the lactase enzyme. The LCT gene is responsible for the production of lactase, and the MCM6 gene is responsible for controlling the expression of the LCT gene. Mutations to the LCT gene may result in congenital lactase deficiency. It's an autosomal inheritance that requires one mutated gene from each parent. Congenital lactase deficiency is a rare form of lactose intolerance that begins at birth. It may severely inhibit the baby's ability to digest milk and milk-based formulas. 

Primary Adult Lactase Deficiency 

Primary adult lactase deficiency is a common form of lactose intolerance. It is linked to the decreased production of lactase in adults. The affected individual will be less likely to digest lactose due to this condition suitably. The intensity of the condition may vary depending on the ethnic and racial makeup. The MCM6 gene regulates the functions of the LCT gene. This will result in a decrease in lactase production over time (or non-persistence). Northern European people primarily have an inherited MCM6 gene mutation that could lead to persistence in digesting lactose in adulthood. People who don't have this mutation will lose the ability to produce lactase as they grow old, which may result in lactose intolerance in the long run.  

Secondary Lactose Intolerance 

The symptoms of lactose intolerance are also prevalent in other gastrointestinal conditions, usually caused by a disease or damage to the small intestine lining. This can lead to the loss of lactase. Your healthcare provider can perform certain tests to determine the various conditions that have similar symptoms. Different conditions have different prognoses and treatments. Treating the primary condition can reverse the secondary lactose intolerance condition.

Here are some other conditions that have symptoms that are similar to Lactose Intolerance

  • Crohn's disease 
  • Celiac sprue 
  • Whipple disease 
  • Bacterial growth syndrome 
  • Short bowel syndrome 
  • AIDS 
  • Tropical sprue 
  • Giardia infections 
  • Cystic fibrosis 
  • Radiation or chemotherapy 
  • Zollinger Ellison syndrome 

Laboratory Tests for Lactose Intolerance 

The goal of lab tests for lactose intolerance is to diagnose the condition and distinguish it from other conditions with similar symptoms.

  • Hydrogen breath test – This is the most effective lab test to diagnose lactose intolerance at this time. Breath samples of the patient are taken before (as the baseline) and at times after the person drinks a fluid with lactose. Hydrogen is produced in excess in the large intestines in a person who suffers from lactose intolerance. This hydrogen moves to the circulation system and eventually is exhaled by the lungs. Increased levels of hydrogen in the breath over time is a strong indicator of a lactose intolerance condition. Lactose tolerance blood test – Blood samples are tested for glucose at different times – once an oral dose of lactose is given to the person. If the glucose level in the blood doesn't rise, lactose intolerance may be present. This test is rarely ordered in a clinical environment. 
  • Stool Acidity pH test – This test is usually performed on infants and kids who cannot undergo other tests. Stools will become acidic when lactose intolerance is present.   

Is there a Cure for Lactose Intolerance?

There is no "cure" for lactose intolerance, but there are many ways to make the condition more tolerable. Such methods include:

  • Limiting milk/dairy intake
  • Consuming milk/dairy products formulated to be lactose-free
  • Taking tablets/powders that contain lactase when ingesting dairy
  • Taking probiotics to improve digestive response

For most people, lactose intolerance does not severely impact the quality of their life. The most serious treatment is eliminating milk and dairy altogether, which is getting easier due to the increase in milk/dairy alternative products.

Sign up for Lactose Intolerance Tests Today!

At Ulta Lab Tests, we offer highly accurate and reliable tests - including lactose intolerance tests. Not only that, but we provide confidential results and don't require insurance or physician referrals. To top it off, our testing service is the most affordable out there.

After you get tested, your confidential results will be delivered online to your private patient portal within 24 to 48 hours for most tests. So take control over your health by ordering a lactose intolerance test now.