Name the marker before you buy the bottle

How much of the fat in your red blood cells is EPA and DHA, the two main fish oil fats. It shows how much oily fish or fish oil you take in. It does not diagnose heart disease.

The storage form of vitamin D made by the liver, and the test used to judge whether someone is short. It is not the active hormone form, 1,25-dihydroxy vitamin D.

Magnesium measured inside red blood cells, not in the liquid part of blood (serum). Serum holds about 0.3 percent of the body's magnesium. That is why a normal serum number can hide low stores in the body.

A protein in blood that shows how much iron is stored. It rises when iron stores are high. It also rises when something in the body is inflamed.

The group of tests that goes with ferritin: serum iron, transferrin or TIBC, and transferrin saturation (how full your iron carriers are). Together they tell you whether iron stores are empty, locked away, or too full.

The share of the oxygen-carrying protein in red blood cells (hemoglobin) that has sugar stuck to it. It estimates your average blood sugar over about three months.

Blood sugar in the morning after a night without food. One day, not a three-month average.

Insulin in the morning before food. Together with fasting blood sugar, it helps estimate how hard your body has to work to control blood sugar (insulin resistance). It is not a test everyone needs.

A count of the particles in your blood that can build plaque in your arteries. Each LDL, VLDL and Lp(a) particle carries one ApoB.

The cholesterol carried inside LDL particles. It is often worked out by formula from a standard cholesterol panel.

A sensitive blood test for inflammation. It does not diagnose any disease, and it rises for many reasons.

Enzymes that leak into the blood when liver cells are under stress. GGT also rises with alcohol and with problems in the bile ducts.

An amino acid the body clears using folate, B12 and B6. Blood levels fall when you take those vitamins, if a shortage of them was the problem.

TSH is the signal from a gland in the brain (the pituitary) that tells the thyroid to work. Free T4 is the thyroid hormone floating free in the blood. Together they are the usual first thyroid tests.

The everyday basic blood panel: sodium, potassium, chloride, bicarbonate, creatinine and eGFR (kidney function), and often blood sugar and calcium. Serum magnesium is sometimes added, and it is still not red blood cell magnesium.

A particle like LDL with an extra protein attached, apo(a). Your genes set its level. Diet and most supplements barely move it.