No, magnesium is not included in a complete blood count (CBC). A CBC measures blood cells and their characteristics, not minerals or electrolytes. If you want your magnesium levels checked, you need a separate blood test ordered specifically for that purpose.
What a CBC Actually Measures
A CBC is one of the most commonly ordered blood tests, but its scope is limited to counting and analyzing the cells in your blood. It measures red blood cells (which carry oxygen), white blood cells (which fight infection), and platelets (which help with clotting). It also reports hemoglobin, hematocrit (the percentage of your blood made up of red blood cells), and mean corpuscular volume (the average size of your red blood cells).
That’s it. A CBC tells your provider about the cellular makeup of your blood. It does not measure any minerals, vitamins, electrolytes, or proteins floating in your blood plasma. Magnesium falls into the mineral/electrolyte category, so it’s completely outside the scope of a CBC.
Magnesium Isn’t in Metabolic Panels Either
This surprises many people: magnesium is also not included in the two other routine blood panels most providers order. A basic metabolic panel (BMP) measures 8 substances, including glucose, calcium, sodium, potassium, and kidney markers. A comprehensive metabolic panel (CMP) expands that to 14 substances by adding liver enzymes, albumin, total protein, and bilirubin. Neither panel includes magnesium.
So if you’ve had “standard bloodwork” done at a checkup, your magnesium level was almost certainly not checked. Calcium, sodium, and potassium get measured routinely, but magnesium requires its own standalone order. This is one reason magnesium deficiency often goes undetected.
How to Get Your Magnesium Tested
You need to ask your provider to order a serum magnesium test specifically. It’s a simple blood draw from a vein in your arm, and there’s usually no special preparation required. If you’re having other blood tests done at the same time that require fasting, you may need to skip food and drink for several hours beforehand. Let your provider know about any supplements or medications you’re taking, since these can affect the results.
The normal range for adults is 1.3 to 2.1 mEq/L. Levels below 0.5 mEq/L or above 3 mEq/L are considered potentially dangerous and typically prompt immediate medical attention. Children and newborns have slightly different ranges.
Cost varies depending on where you go. Based on recent data, prices range from roughly $41 at some national labs to $89 as a statewide average, though your insurance may cover part or all of the cost if your provider orders it for a medical reason.
Serum vs. RBC Magnesium Tests
The standard test measures magnesium in your blood serum, which is the liquid portion of your blood. This is the most widely available and commonly ordered version. However, only about 1% of the magnesium in your body is in your blood. The rest is stored in your bones, muscles, and soft tissues. This means a serum test can sometimes come back normal even when your body’s overall magnesium stores are low.
An RBC magnesium test measures the magnesium inside your red blood cells rather than in the surrounding fluid. Some practitioners consider this a better reflection of your body’s true magnesium status, since intracellular levels change more slowly than serum levels. RBC magnesium testing is less commonly offered and may not be available at every lab, but it’s worth asking about if you suspect a deficiency despite normal serum results.
When Magnesium Testing Makes Sense
Providers typically order a magnesium test when someone has symptoms that could point to low or high levels. Muscle cramps, twitching, tremors, heart rhythm irregularities, persistent fatigue, and numbness or tingling can all be signs of magnesium imbalance. People with chronic kidney disease, digestive conditions that affect nutrient absorption, poorly controlled diabetes, or long-term alcohol use are at higher risk for deficiency and may benefit from periodic testing.
Certain medications can also deplete magnesium over time, particularly proton pump inhibitors (used for acid reflux) and some diuretics. If you’re on one of these long-term, testing every so often can catch a gradual decline before symptoms develop. Since magnesium isn’t part of any routine panel, the only way to know your level is to specifically request the test.