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Biomarker guides
A biomarker is a measurable signal in your blood that reflects how a body system is working. These guides explain what each marker measures, the commonly used reference ranges, and which panels include it.
Heart Health
Apolipoprotein B
Measured in mg/dL
Apolipoprotein B (ApoB) measures the total number of atherogenic lipoprotein particles in your blood, since each LDL, VLDL, and Lp(a) particle carries exactly one ApoB protein. People test it because particle count is increasingly viewed as a more direct gauge of cardiovascular risk exposure than LDL cholesterol alone.
LDL Cholesterol
Measured in mg/dL
LDL cholesterol (LDL-C) measures the amount of cholesterol carried by low-density lipoprotein particles, the particles most closely associated with plaque buildup in arteries. It is the most widely tracked lipid marker, and people test it to monitor cardiovascular health and the effect of diet, lifestyle, or medication.
HDL Cholesterol
Measured in mg/dL
HDL cholesterol (HDL-C) measures the cholesterol carried by high-density lipoprotein particles, which transport cholesterol away from tissues back to the liver. People test it as part of a standard lipid panel because low HDL-C is associated with higher cardiovascular risk and often travels with insulin resistance.
Triglycerides
Measured in mg/dL
Triglycerides measure the amount of fat circulating in your blood, largely reflecting how your body processes dietary carbohydrate and fat. People test them as part of a lipid panel because elevated triglycerides are associated with cardiovascular risk and are one of the earliest lab signals of insulin resistance.
Lipoprotein(a)
Measured in nmol/L
Lipoprotein(a), or Lp(a), measures a genetically determined lipoprotein particle that is independently associated with cardiovascular and aortic-valve disease. People test it, usually once in a lifetime, because levels are largely set by genes, and an elevated result reframes how aggressively other risk factors are worth managing.
hs-CRP
Measured in mg/L
High-sensitivity C-reactive protein (hs-CRP) measures low-grade inflammation in the body, detecting levels far below what a standard CRP test can see. People test it because chronic low-level inflammation is associated with cardiovascular risk, and hs-CRP adds a dimension that cholesterol numbers alone do not capture.
Thyroid Health
TSH
Measured in µIU/mL
Thyroid-stimulating hormone (TSH) measures the pituitary signal that tells the thyroid how much hormone to make, making it the standard first-line thyroid screening test. People test it to check whether the thyroid is keeping pace with the body’s needs, since both fatigue-like and overactive symptoms can trace back to thyroid function.
Free T3
Measured in pg/mL
Free T3 measures the unbound, biologically active form of triiodothyronine, the thyroid hormone that actually drives metabolism at the cellular level. People test it alongside TSH and Free T4 to see whether the body is successfully converting stored thyroid hormone into its active form.
Free T4
Measured in ng/dL
Free T4 measures the unbound thyroxine circulating in your blood, the thyroid’s main output and the raw material for active T3 hormone. People test it with TSH to confirm whether the thyroid is actually delivering hormone, since TSH alone only shows the demand signal.
Blood Sugar
Fasting Glucose
Measured in mg/dL
Fasting glucose measures the amount of sugar circulating in your blood after at least eight hours without food. It is one of the most widely used markers of blood-sugar regulation, and people test it to track metabolic health over time and to see where they fall relative to commonly used reference ranges.
Hemoglobin A1c
Measured in %
Hemoglobin A1c (HbA1c) measures the percentage of hemoglobin in red blood cells that has glucose attached, reflecting average blood sugar over roughly the past three months. People test it because it smooths out day-to-day swings, making it one of the most useful single markers for tracking long-term glucose control.
Fasting Insulin
Measured in µIU/mL
Fasting insulin measures how much insulin your pancreas is producing after an overnight fast. People test it because it can reveal how hard the body is working to keep glucose normal, insulin often rises years before fasting glucose or HbA1c drift out of range.
Women's Health
Men's Health
Nutrients & Vitamins
Vitamin D (25-OH)
Measured in ng/mL
The 25-hydroxy vitamin D test measures your body’s stored vitamin D, reflecting weeks of sun exposure, diet, and supplementation combined. People test it because vitamin D supports bone, muscle, and immune function, and low levels are among the most common findings on routine blood work, especially in winter and at higher latitudes.
Ferritin
Measured in ng/mL
Ferritin measures the protein that stores iron in your cells, making it the standard blood marker of the body’s iron reserves. People test it to investigate fatigue, heavy periods, endurance-training demands, or restless legs, and because low iron stores are among the most common and most fixable lab findings.
Organ Health
eGFR
Measured in mL/min/1.73m²
eGFR (estimated glomerular filtration rate) estimates how many milliliters of blood your kidneys filter per minute, calculated from blood creatinine along with age and sex. It is the standard measure of kidney function, and people test it because kidney decline is typically silent until it is advanced.
ALT
Measured in U/L
ALT (alanine aminotransferase) measures an enzyme concentrated in liver cells that leaks into the blood when those cells are stressed or damaged. It is the most liver-specific of the standard enzymes, and people test it to track liver health, particularly relevant given how common fatty liver has become.