Your lab markers, one by one

ApoB and LDL cholesterol

LDL cholesterol measures how much cholesterol is carried in LDL particles. ApoB counts the particles themselves, because each potentially plaque-forming particle carries one ApoB protein. Usually the two move together, but in people with insulin resistance, high triglycerides or type 2 diabetes, ApoB can be high even when LDL looks fine, suggesting more, smaller particles. Diet, exercise, weight loss and medications such as statins can lower ApoB.

Lipoprotein(a)

Lp(a) is a cholesterol-carrying particle whose level is mostly inherited. The American Heart Association recommends that every adult be tested at least once, and notes that it matters especially if you have a family history of early heart disease or familial hypercholesterolemia. Lifestyle changes do not meaningfully lower Lp(a), but they still lower your overall risk, and a high Lp(a) is a reason to manage ApoB, blood pressure and other factors more aggressively. It is not included in a standard lipid panel, so it must be ordered.

hs-CRP

High-sensitivity C-reactive protein is a general marker of inflammation. It rises with infections, injuries, hard training, poor sleep and excess body fat, so one high reading tells you little. Repeating it a few weeks later, when you are well, gives a clearer picture. Persistently elevated hs-CRP can add to cardiovascular risk assessment and may prompt a search for an inflammatory cause.

Ferritin and iron

Ferritin reflects stored iron and often drops before anemia appears, which is why your hemoglobin can be normal while iron stores are low. Low ferritin can contribute to fatigue and hair shedding. But ferritin also rises with inflammation, liver disease, heavy alcohol use and obesity, so a normal or high value does not always mean plenty of iron. High ferritin can reflect iron overload and deserves follow-up. Do not start iron supplements without testing; too much iron is harmful.

A1c, fasting insulin and HOMA-IR

According to the CDC, an A1c below 5.7% is normal, 5.7% to 6.4% indicates prediabetes and 6.5% or higher indicates diabetes. A1c reflects about three months of average blood sugar and changes slowly, so retesting sooner than three months says little. Anemia, kidney or liver disease and some blood disorders can make it misleading.

Fasting insulin can rise for years before glucose does, so it can reveal early insulin resistance. HOMA-IR combines fasting glucose and insulin into one estimate. Neither is a diagnosis on its own, and both are best tracked within the same person and lab over time, alongside waist size and blood pressure.

Thyroid: TSH, free T4 and free T3

TSH comes from the pituitary and tells the thyroid how hard to work. A high TSH suggests an underactive thyroid and a low TSH an overactive one. It is a good first test, but it cannot show the cause; free T4, free T3 and thyroid antibodies add detail when TSH is abnormal or symptoms persist. Biotin supplements can interfere with some thyroid tests, and severe calorie restriction can lower thyroid hormone levels.

Vitamin D

The blood test measures 25-hydroxyvitamin D. The NIH Office of Dietary Supplements describes 20 ng/mL (50 nmol/L) or higher as adequate for most people and below 12 ng/mL (30 nmol/L) as too low. Levels above 50 ng/mL (125 nmol/L) are considered too high, and very high levels almost always come from supplements. Retesting after a few months of supplementation helps avoid overshooting.

SHBG, DHEA-S, cortisol and hematocrit

SHBG binds testosterone and estradiol, so it changes how much is available to tissues; high SHBG can make a normal total testosterone less meaningful. DHEA-S falls with age and is not a measure of stress. A single cortisol value is a snapshot of a hormone with a strong daily rhythm and cannot diagnose everyday stress. Hematocrit, the share of blood made up of red cells, is monitored on testosterone therapy because it can rise; dehydration can also nudge it up.