Magnesium Blood Test Cost and Medicare Coverage (CPT 83735)

Also called: serum magnesium · Mg test · magnesium level — all the same test, CPT 83735.

The short answer

Only when something in your situation genuinely depletes or disturbs magnesium — not “let’s check your minerals.” Regional Medicare policies cover the magnesium test for a specific set of conditions and medications known to drain it. Ordered that way, it’s covered and costs you $0. Ordered inside a wellness or nutrient panel for general interest — the way magnesium is most often marketed — it’s screening, and screening is denied. Medicare pays the lab just $6.70 for this test, a number worth remembering at any signature pad.

When Medicare DOES cover it

The covered picture (from one regional policy, LCD L36702):

• Electrolyte problems being investigated — low calcium or low potassium often travel with low magnesium, so an abnormal result on those triggers a covered magnesium check
• Medications that deplete magnesium — diuretics (“water pills”), certain heart-rhythm drugs (patients on those get magnesium checked about every 6 months), some chemotherapy and long-term acid reducers
• Conditions that drain it — malabsorption, alcohol-related malnutrition, poorly controlled diabetes, hyperparathyroidism
• Kidney disease and dialysis, where magnesium balance needs watching
• Symptoms of deficiency — muscle weakness, tremors, cramping, or heart-rhythm disturbances being worked up
• Long-term IV nutrition — checked monthly

When Medicare does NOT cover it

• Routine screening — magnesium “just to see,” with no qualifying condition, medication, or symptom
• Wellness and micronutrient panels — treated as screening categorically

If your test gets flagged, ask your doctor which covered situation applies to you. (Never ask anyone to change a code just to get coverage — that’s fraud. But doctors often have a legitimate reason for the test that simply wasn’t coded.)

What you pay if it IS covered: $0

Covered lab tests cost Medicare patients nothing — no deductible, no 20% coinsurance. Medicare pays the lab $6.70, and you owe zero.

What you pay if it is NOT covered — read this before you sign

1. Ask the lab to print exactly what you would owe. You’re entitled to the number first. For perspective: Medicare pays the lab $6.70 for this exact test.
2. Know the direct prices: $15 at Jason Health (jasonhealth.com — add their flat $18 lab-collection fee per order) and $39 at both Quest’s consumer site (questhealth.com, plus a $6 physician fee) and Labcorp OnDemand. Same certified labs, same blood draw.

Before you sign the pad — 60-second checklist

1. Ask: “Can you print what I’ll owe if Medicare doesn’t pay?”
2. Ask your doctor: “Which of my conditions or medications makes this test necessary?”
3. Compare the printed price to the direct-purchase prices before deciding.

What counts as a “normal” magnesium level

Start with the range printed on your own report. There is no single published standard to compare it with. Unlike blood sugar or cholesterol, no major medical body publishes an agreed cut-off for this test, so each laboratory sets its own from its own sample of people on its own equipment. Two labs can report the same blood differently.

There is a further wrinkle with magnesium: most of the body’s supply sits inside cells and bone rather than in the blood, so a blood level is an indirect measure of your overall status.

(Where lab ranges and “optimal” ranges come from, and who decides.)

This page can tell you where those numbers came from. It cannot tell you what yours means — that reading belongs to your doctor, alongside your history and your other results.

Quick questions people ask

What is the magnesium blood test called? You’ll see it written several ways: serum magnesium, magnesium level, Mg, or just “magnesium” on the lab slip — all the same test, CPT code 83735. (A different version, “RBC magnesium,” measures magnesium inside red blood cells — a separate test with a separate code that Medicare treats separately.)

What blood test checks magnesium — is it part of regular blood work? Not automatically. Magnesium is not included in the basic or comprehensive metabolic panels — it’s its own order and its own line on the bill, which is exactly how it ends up on a signature pad when the rest of the panel sails through.

Do you have to fast for a magnesium test? No — fasting isn’t required, though it’s often drawn with tests that do require it. Follow your order’s instructions. See our guide to fasting before blood work.

Sources and data dates

Medicare payment amount: CMS Clinical Laboratory Fee Schedule, 2026 Q3 file (national rate). Coverage rules: CMS Medicare Coverage Database, LCD L36702 (a regional policy used here as the example — your region’s policy may differ in details). Consumer prices checked September 2026. Information current as of the date shown above; coverage is always determined by Medicare when your claim is processed.

ClaraCover provides information, not medical, billing, or insurance advice. Talk to your doctor about what tests you need.