Serum magnesium measures the level of magnesium in your blood. While useful for detecting severe deficiency, it may not reflect your true magnesium status since most magnesium is stored in cells and bones.
Magnesium is the fourth most abundant mineral in the body and is essential for over 300 enzymatic reactions, including muscle and nerve function, blood sugar control, blood pressure regulation, protein synthesis, and energy production.
This test measures magnesium in blood serum. It's important to understand that serum magnesium represents only about 1% of total body magnesium—the rest is in cells, bones, and tissues. The body tightly regulates serum magnesium, pulling from stores to maintain blood levels even when you're becoming deficient.
Because of this, serum magnesium is better at detecting severe or acute deficiency than mild or chronic insufficiency. If you have symptoms of magnesium deficiency but normal serum levels, consider RBC (red blood cell) magnesium for a more accurate assessment of your cellular magnesium status.
Price
$7
Results
1 days
Lab Network
Quest
Fasting
Not Required
What's Measured
What This Test Measures
This test measures magnesium concentration in blood serum, reported in mg/dL or mEq/L. Normal range is typically 1.7-2.3 mg/dL (1.4-1.9 mEq/L). Low serum magnesium (<1.7 mg/dL) indicates deficiency. Critically low (<1.2 mg/dL) can cause serious symptoms.
Who Should Consider This Test
People with muscle cramps or spasms, those with heart arrhythmias or palpitations, individuals on diuretics or PPIs long-term, diabetics (magnesium is commonly low), people with alcoholism, those with digestive conditions affecting absorption, and anyone with severe or acute symptoms suggesting deficiency.
Health Insights
Conditions Screened
Related Symptoms
When to Get Tested
No fasting required. Serum magnesium can be tested any time. Note that normal serum magnesium does not rule out deficiency—for a more comprehensive assessment, consider RBC magnesium.
Understanding Your Results
Normal: 1.7-2.3 mg/dL. Low (<1.7 mg/dL): deficiency likely, may cause symptoms. Critically low (<1.2 mg/dL): severe deficiency, can cause dangerous heart rhythm issues. High (>2.6 mg/dL): usually from kidney failure or excess supplementation, can cause weakness and cardiac effects.
What to Expect
After placing your order, you'll receive an email from Rupa Health (our lab order partner) within 24 business hours to sign a consent form and schedule your blood draw at a Quest Diagnostics location.
The blood draw typically takes just a few minutes. Results are usually available within 1 business days and will appear in your secure Justlabs dashboard.
Our results include reference ranges and easy-to-understand indicators showing whether your values are within normal limits.
Frequently Asked Questions
$7
Typical hospital cash price: $100–$200
+ $28 in standard lab & physician fees at checkout (no additional bills later)
$18 lab collection + $10 physician order
Need Help Choosing?
Not sure if this is the right test for you? Take our quick questionnaire.
Take the QuizRelated Tests
RBC Magnesium
Magnesium, RBC
$15
Measures magnesium inside red blood cells. More accurate than serum magnesium for assessing true status.
Biomarkers:
RBC Magnesium
Vitamin D
Vitamin D, 25-Hydroxy
$22
Measures vitamin D status. Deficiency is common and linked to bone health, immune function, and mood.
Biomarkers:
Vitamin D, 25-OH
BMP
Basic Metabolic Panel
$6
Measures 8 substances including glucose, electrolytes, and kidney function markers.
Biomarkers:
Glucose, BUN, Creatinine +6 more
$7
+ $28 in fees