Ulta Lab Tests

Magnesium Deficiency

Magnesium deficiency (hypomagnesemia) can affect muscles, nerves, heart rhythm, and energy. Because only a small fraction of magnesium circulates in blood, symptoms can appear even when a basic serum level looks “normal.” A stepwise, lab-first approach helps clarify status and uncover why levels are low—reduced intake, poor absorption, or increased loss through the kidneys.

Most evaluations start with serum magnesium and RBC magnesium (a medium-term, cell-associated measure). Your clinician may add potassium and calcium (often low when magnesium is low), kidney function (creatinine/CMP), and, when the cause is unclear, a 24-hour urine magnesium to distinguish renal wasting from low intake or malabsorption. Testing supports screening, diagnostic triage, and monitoring, but does not replace your clinician’s exam, ECG when indicated, or emergency care.

Signs, Symptoms & Related Situations

  • Muscle & nerve: cramps, twitching, tremor, muscle weakness, numbness/tingling, migraines

  • Energy & mood: fatigue, brain fog, irritability, poor sleep

  • Heart rhythm: palpitations, skipped beats; severe deficiency can contribute to arrhythmias

  • Electrolyte clues: low potassium or calcium that is “hard to fix”

  • Digestive & absorption risks: chronic diarrhea, celiac disease, inflammatory bowel disease, bariatric surgery, alcohol use disorder

  • Medication flags: long-term PPIs, loop/thiazide diuretics, some antibiotics/chemotherapy (e.g., aminoglycosides, cisplatin)

  • Metabolic context: diabetes/insulin resistance, high stress, endurance training with heavy sweat losses

  • Seek urgent care now: chest pain, severe shortness of breath, fainting, seizures, or new neurologic deficits

Symptoms are nonspecific and should be evaluated by a qualified clinician.

Why These Tests Matter

What testing can do

  • Confirm low magnesium and reveal related electrolyte patterns (potassium, calcium, phosphorus)

  • Differentiate causes: low intake/absorption vs renal loss (24-hr urine)

  • Guide monitoring after diet changes, medication review, or clinician-directed therapy

What testing cannot do

  • Diagnose heart rhythm problems by itself—ECG and clinical evaluation are separate

  • Provide dosing or treatment advice without clinician oversight

  • Eliminate pre-analytical issues (e.g., hemolysis can falsely raise serum magnesium) without proper collection

What These Tests Measure (at a glance)

  • Magnesium, Serum: widely used first test; reflects circulating magnesium but can be normal in deficiency.

  • Magnesium, RBC: cell-associated measure reflecting medium-term status; complements serum magnesium.

  • Magnesium, 24-Hour Urine: helps determine renal wasting (higher urinary magnesium) vs low intake/absorption (lower urinary magnesium).

  • Electrolytes & context: Potassium, Calcium, Phosphorus, Creatinine/CMP (kidney function), PTH and Vitamin D when calcium is low, ± ECG if symptoms warrant (performed outside the lab menu).

  • Pre-test notes: fasting is usually not required. Avoid magnesium supplements the morning of a serum draw to prevent a transient bump. Report medications. Avoid sample hemolysis, which can artifactually elevate serum magnesium.

Quick Build Guide

Goal / Scenario Start with Add if needed
First-line deficiency check Serum Mg • RBC Mg • CMP (incl. creatinine) • Potassium • Calcium Phosphorus • Vitamin D • PTH if calcium is low
Unclear cause / recurrent low Mg Serum Mg • RBC Mg 24-hr Urine Mg to assess renal loss vs intake/absorption
Low K? or Ca²? that won’t correct Serum Mg • RBC Mg • Potassium • Calcium Phosphorus • PTH • Vitamin D
GI malabsorption / bariatric / chronic diarrhea Serum Mg • RBC Mg • CMP Iron/ferritin • B12 ± MMA • Folate • Vitamin D
Medications (PPIs/diuretics/cisplatin) Serum Mg • RBC Mg 24-hr Urine Mg • Potassium • Calcium
Diabetes/insulin resistance or heavy training Serum Mg • RBC Mg • CMP A1c • Fasting glucose • Potassium

How the Testing Process Works

  1. Match tests to your goal: begin with serum + RBC magnesium and essential electrolytes.

  2. Prepare for accuracy: no routine fasting; skip a large magnesium supplement dose the morning of your draw if advised. List all medicines (PPIs, diuretics).

  3. Provide samples: blood draw for serum/RBC tests; 24-hour urine for urinary magnesium when ordered.

  4. Get secure results: most post within a few days.

  5. Plan next steps: review with your clinician to confirm the cause (intake, absorption, renal losses) and set a monitoring schedule.

Interpreting Results (General Guidance)

  • Low serum magnesium → consistent with deficiency; confirm context with RBC magnesium and electrolytes.

  • Normal serum, low RBC magnesium → possible tissue-level shortfall; interpret with symptoms and risk factors.

  • High 24-hr urinary magnesium with low blood magnesium → suggests renal wasting (e.g., diuretics, certain drugs).

  • Low 24-hr urinary magnesium with low blood magnesium → suggests low intake or malabsorption.

  • Low K? and/or Ca²? with low magnesium → magnesium repletion is often required before these normalize (management is clinician-directed).
    Always interpret results with a qualified healthcare professional; trends over time and clinical context matter more than one value.

Choosing Panels vs. Individual Tests

  • Core magnesium panel: Serum Mg • RBC Mg • CMP • Potassium • Calcium

  • Cause-finding add-on: 24-hr Urine Mg (renal vs GI losses)

  • Calcium/bone context: Phosphorus • PTH • Vitamin D when calcium is low

  • Malabsorption context: Iron/ferritin • Vitamin B12 ± MMA • Folate
    Use bundled panels for efficiency; add targeted markers to answer specific questions and monitor progress.

FAQs

Is RBC magnesium better than serum magnesium?
They answer different questions. Serum reflects circulating levels; RBC offers a medium-term, cell-associated view. Many clinicians use both.

Do I need to fast?
Usually no. Avoid taking a magnesium supplement right before a serum draw unless your clinician says otherwise.

When is a 24-hour urine magnesium helpful?
When levels stay low despite changes—this test helps tell renal loss from low intake/absorption.

Which medicines lower magnesium?
Common ones include PPIs and diuretics; some antibiotics and chemotherapy drugs can also increase losses. Share your full medication list.

Can low magnesium cause low potassium or calcium?
Yes. Magnesium deficiency can make potassium and calcium harder to correct.

How often should I re-test?
Many people recheck in 6–12 weeks after clinical or lifestyle changes—your clinician will set the cadence.

Related Test Categories & Key Tests

  • All Vitamin & Mineral Tests

  • Micronutrient Testing • Iron Studies & Anemia • Metabolism Tests • Kidney Health Tests • Heart Health Tests

  • Key Tests: Magnesium (Serum) • Magnesium (RBC) • Magnesium (24-hr Urine) • Potassium • Calcium • Phosphorus • PTH • Vitamin D (25-OH) • CMP • Creatinine • Iron • Ferritin • B12 • MMA • Folate • A1c

References

  • NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals.
  • American Association for Clinical Chemistry — Guidance on magnesium measurement and pre-analytical factors.
  • National Kidney Foundation — Electrolyte disorders and evaluation of renal magnesium wasting.
  • American College of Gastroenterology — Malabsorption evaluation and micronutrient assessment.
  • American Heart Association — Electrolytes and arrhythmia risk statements.
  • Clinical reviews on serum vs RBC magnesium and the diagnostic role of 24-hour urinary magnesium.

Available Tests & Panels

Your Magnesium Deficiency Tests menu is pre-populated in the Ulta Lab Tests system. Start with the core magnesium panel (serum and RBC magnesium with electrolytes). Use filters to add a 24-hour urine magnesium to clarify renal losses and calcium/bone or malabsorption markers when indicated. Follow any collection instructions and review results with your clinician to confirm the cause and set a monitoring plan.

Magnesium Deficiency Lab Tests FAQ

How often do you think about your mineral levels? 

Unless you're a professional athlete, doctor, or nutritionist, it probably doesn't cross your mind more than once a year at your annual physical. If you're taking a multivitamin, that's even better than most!

Magnesium is crucial to the body's muscle, hormonal, and nerve function. Without it, you're likely feeling tired, crampy, and anxious. You may have a hard time focusing and struggle to sleep, digest meals, or enjoy sex. 

Magnesium blood tests are the first look into what your body may be lacking. Read on to understand how magnesium deficiency feels and how the correct magnesium deficiency test can start you on the right track to functional healing.   

Risk Factors For Magnesium Deficiency 

Some populations are at a higher risk for magnesium deficiency. These include: 

  • Diabetics
  • Those with an unhealthy diet 
  • Pregnant women
  • Those taking medications that inhibit magnesium stores in the body 
  • Those with vitamin D deficiency 
  • Those with gastrointestinal conditions
  • Alcoholics

If you fall under any of these groups, it might be worth getting tested.  

Causes of Magnesium Deficiency 

Magnesium deficiency is caused by the body's inability to properly absorb the mineral in the gut or excess magnesium loss through the body's waste. In addition, kidney problems may affect magnesium excretion, as it is the kidney's responsibility to determine optimal levels in the body. 

Magnesium levels are also known to take a hit during pregnancy.  

Nutrition lacking in essential vitamins and minerals may also affect magnesium levels. 

Signs and Symptoms of Magnesium Deficiency

Magnesium is a metabolic necessity in our bodies. It's needed in optimal amounts for your bones, muscles, nerves, digestive tract, hormones, blood sugar, and heart. 

Magnesium deficiency can range from barely noticeable to extremely uncomfortable. Signs and symptoms of magnesium deficiency include: 

  • Muscle cramping
  • Depression and anxiety 
  • Osteoporosis 
  • Fatigue and poor sleep 
  • High blood pressure and heart arrhythmia 
  • Poor appetite
  • Nausea 
  • Weakness 
  • Headaches
  • Low levels of other minerals - like calcium and potassium 

Having any one of a few of these symptoms may not necessarily point to a deficiency. It will take a lab test to determine if you are. 

Lab Tests for Magnesium Deficiency  

Your doctor will require a magnesium deficiency lab test to screen, diagnose and monitor your condition. To confirm that you are magnesium deficient, a doctor may request a urine sample, though a blood test is most efficient. 

A magnesium deficiency test is also known as a serum magnesium test. Its purpose is to measure the amount of magnesium in the blood–-though a majority of the body's magnesium stores are found in the bones. 

You can initiate your blood draw from one of 2,100 state and federally certified blood-draw centers near your home. Once your specimen is collected, it is sent to Quest Diagnostics to process, and your results will be available for you to view on your Ulta Lab Tests dashboard.

An optimal blood (serum) magnesium level is is 1.8 to 2.2 milligrams per deciliter (mg/dL). Anything lower than this range may be diagnosed by your doctor as hypomagnesemia and will need an immediate treatment plan. 

Magnesium Deficiency Lab Tests FAQ

If this is all very new to you, don't worry! We have a dedicated team prepared to answer your questions and an intuitive website to easily select and order your tests and review your results.

What are the types of magnesium deficiency? 

Though there is a singular metric for magnesium deficiency in the human body, there are a few different types of magnesium. These include: 

  • Magnesium citrate - extremely bioavailable source of magnesium naturally found in citrus fruits and supplements
  • Magnesium oxide - not typically used for magnesium deficiencies, but valuable for soothing digestive symptoms  
  • Magnesium chloride - easily absorbed in the digestive system and used for treating low magnesium levels, heartburn, and constipation
  • Magnesium lactate - often taken by those who need high levels of magnesium 
  • Magnesium malate - a gentle supplemental form of magnesium 
  • Magnesium taurate - supports healthy blood pressure 
  • Magnesium L-threonate - known for increasing magnesium levels in brain cells
  • Magnesium sulfate - used to soothe achy muscles-- also known as Epsom salt
  • Magnesium glycinate - magnesium with calming properties
  • Magnesium orotate - used to treat symptoms of severe congestive heart failure and blood pressure disorders

Once you receive your lab results, you can work with your healthcare professional to determine the best course of action. 

Who should be tested for magnesium deficiency? 

If you meet any of the above risk factors, are experiencing low libido, poor sleep, or lethargy, you may want to get tested for magnesium deficiency. Improving your magnesium levels may improve your quality of life. 

How is magnesium deficiency diagnosed? 

Magnesium deficiency, or hypomagnesemia, will appear on a blood test. Once you have received your convenient results, your doctor will determine your next course of action. 

Are results shared privately? 

Yes, we provide secure and confidential results. You may access your results within your private online account. 

Do you require insurance or a doctor's referral to receive magnesium deficiency testing? 

No, you may purchase lab testing without insurance or a doctor's note. Our tests are for those who want to take a proactive role in monitoring their health. 

How do you approach customer service? 

Finally, we provide a 100% satisfaction guarantee. If you aren't happy with our service, we'll work to make it right.

Magnesium Blood Tests With Ulta Lab Tests

Are you dealing with the fallout of a potential magnesium deficiency? A magnesium blood test is just one test away from feeling confident and in control of your body.

Ulta Lab Tests offers tests that are highly accurate and reliable so that you can make informed decisions about your health. Here are a few great things to love about Ulta Lab Tests:

- You'll get secure and confidential results
- You don't need health insurance
- You don't need a physician's referral
- You'll get affordable pricing
- We offer a 100% satisfaction guarantee

Order your magnesium deficiency lab test today. The results of our magnesium blood tests can be provided to you securely and confidently online–usually within 24-48 hours!

Take charge of your health and track your progress with Ulta Lab Tests.