Biomarker Encyclopedia
How to interpret your lab results
Plain-English explanations of the 60 most common blood tests — what each marker measures, what high and low values mean, and the follow-up questions worth asking your clinician.
Medically reviewed by Dr. Greg Nigh, ND
Naturopathic Physician, Researcher · Last reviewed July 2026
Educational content only. Not a substitute for care from your own clinician.
Metabolic
- Fasting GlucoseFasting glucose reflects your blood sugar after 8+ hours without food and is the first screen for insulin resistance and diabetes.
- Hemoglobin A1cHbA1c estimates your average blood sugar over the last ~3 months and is the standard test for diagnosing and tracking diabetes.
- Fasting InsulinFasting insulin is the earliest signal of insulin resistance — often elevated years before glucose or A1c move.
- HOMA-IRHOMA-IR uses fasting glucose and insulin to estimate insulin resistance in a single number.
- Uric AcidUric acid is a byproduct of purine metabolism; high levels drive gout and correlate with insulin resistance and hypertension.
Lipids
- LDL CholesterolLDL-C estimates cholesterol carried by LDL particles — a long-standing target for cardiovascular risk, but ApoB and LDL-P give a more accurate particle count.
- HDL CholesterolHDL-C reflects cholesterol carried by HDL particles; moderately high levels correlate with lower cardiovascular risk, but very high HDL is not necessarily protective.
- TriglyceridesFasting triglycerides are a sensitive marker of dietary carbohydrate load and insulin resistance.
- Total CholesterolTotal cholesterol is a sum of LDL, HDL, and VLDL-derived cholesterol — useful as a screen, but nearly useless without the breakdown.
- Apolipoprotein BApoB counts every atherogenic particle (LDL, VLDL, Lp(a)) — the single best cholesterol number for cardiovascular risk.
- LDL Particle NumberLDL-P counts the number of LDL particles directly and is more predictive of risk than LDL-C when the two disagree.
- Lipoprotein(a)Lp(a) is a genetically determined LDL-like particle; high levels are an independent, lifelong cardiovascular risk factor.
Thyroid
- TSHTSH is the pituitary's signal to the thyroid; it rises when the thyroid is underactive and falls when it is overactive.
- Free T4Free T4 is the unbound, active form of thyroxine — the pool available for conversion to the more active T3.
- Free T3Free T3 is the biologically active thyroid hormone that actually drives metabolism at the cell.
- Reverse T3Reverse T3 is an inactive T3 isomer produced under stress; high levels can blunt thyroid signaling even with normal TSH.
- TPO AntibodiesTPO antibodies are the primary marker of autoimmune thyroid disease (Hashimoto's).
Hormones
- Total TestosteroneTotal testosterone measures all testosterone in blood; interpret with free testosterone and SHBG for the full picture.
- Free TestosteroneFree testosterone is the fraction not bound to SHBG or albumin — the bioactive pool that reaches tissues.
- SHBGSHBG binds sex hormones and controls how much is bioavailable; it is exquisitely sensitive to insulin, thyroid, and estrogen.
- Estradiol (E2)Estradiol is the primary estrogen driving reproductive and bone health in women and modulating many tissues in men.
- ProgesteroneProgesterone rises after ovulation and confirms whether a menstrual cycle was ovulatory.
- FSHFSH is the pituitary's signal to grow ovarian follicles or produce sperm; it rises when reproductive reserve declines.
- LHLH triggers ovulation and testosterone production; the LH:FSH ratio helps evaluate PCOS.
- Morning CortisolAM cortisol should peak within an hour of waking; abnormal values suggest adrenal or pituitary issues or disrupted circadian rhythm.
- DHEA-SulfateDHEA-S is an adrenal androgen precursor that declines with age; low levels can reflect chronic stress or adrenal fatigue.
- ProlactinProlactin controls lactation; high levels can disrupt menstrual cycles, fertility, and libido in both sexes.
Inflammation
- hs-CRPhs-CRP is the standard marker of systemic inflammation and a strong independent cardiovascular risk factor.
- ESRESR is an old but useful nonspecific marker of inflammation; it moves more slowly than CRP.
- HomocysteineHomocysteine is a methylation byproduct; high levels reflect B-vitamin deficiency and raise cardiovascular and cognitive risk.
Nutrients
- Vitamin D (25-OH)25-OH vitamin D is the storage form of vitamin D and the standard test for deficiency.
- Vitamin B12Serum B12 is a first-line screen; MMA and homocysteine confirm functional deficiency when B12 is borderline.
- FolateFolate is essential for DNA synthesis and methylation; deficiency causes macrocytic anemia and elevated homocysteine.
- Magnesium (serum)Serum magnesium is insensitive — most magnesium is intracellular — so 'normal' does not rule out deficiency.
- Calcium (serum)Serum calcium is tightly regulated; abnormal values usually point to parathyroid, vitamin D, or kidney issues, not diet.
- ZincZinc is required for immune function, taste, wound healing, and testosterone production.
- CopperCopper works in balance with zinc; excess or deficiency both cause problems.
- SeleniumSelenium is required for glutathione peroxidase and for converting T4 to active T3.
Iron
- FerritinFerritin reflects iron storage — but it also rises with inflammation, so interpret alongside hs-CRP.
- Serum IronSerum iron fluctuates hour-to-hour and is meaningful only alongside TIBC and ferritin.
- TIBCTIBC measures how much iron your transferrin could carry — it rises when iron is low.
- Transferrin SaturationTransferrin saturation is the best functional marker for both iron deficiency and iron overload.
Kidney
- CreatinineCreatinine is a muscle-derived waste product cleared by the kidneys; it is the basis for eGFR.
- eGFReGFR estimates how well your kidneys filter blood and is the primary staging tool for chronic kidney disease.
- BUNBUN reflects protein metabolism and hydration as much as kidney function; interpret with creatinine.
- Cystatin CCystatin C is a more accurate kidney filtration marker than creatinine, especially at extremes of muscle mass.
Liver
- ALTALT is the most liver-specific enzyme and is often the earliest sign of fatty liver.
- ASTAST is present in liver, muscle, and heart; interpret with ALT — the AST:ALT ratio is diagnostic.
- GGTGGT is highly sensitive to alcohol, medications, and oxidative stress in the liver.
- ALPALP comes from liver, bone, and intestine; interpret alongside GGT to localize the source.
- Total BilirubinBilirubin is a heme breakdown product; mild isolated elevations often reflect harmless Gilbert's syndrome.
- AlbuminAlbumin is the liver's main plasma protein and a marker of nutrition, liver function, and chronic disease.
CBC
- HemoglobinHemoglobin measures the oxygen-carrying capacity of blood — the primary screen for anemia.
- HematocritHematocrit is the percentage of blood volume made up of red cells; it tracks with hemoglobin.
- MCVMCV describes the average size of red blood cells and classifies anemia into microcytic, normocytic, or macrocytic.
- RDWRDW measures variation in red-cell size; elevated RDW is an early sign of nutritional or bone-marrow stress.
- White Blood Cell CountWBC count tracks immune activity; high or low values are meaningful only alongside the differential.
- NeutrophilsNeutrophils are the first-line responders to bacterial infection and acute stress.
- LymphocytesLymphocytes handle viral defense and adaptive immunity; the NLR (neutrophil:lymphocyte ratio) is a broad stress and inflammation marker.
- PlateletsPlatelets are cell fragments that drive clotting; abnormal counts can reflect inflammation, bone marrow issues, or splenic dysfunction.
This report is for educational and informational purposes only.
It is not medical advice, diagnosis, or treatment. Always consult your qualified healthcare provider for interpretation of your lab results and any health decisions.