Health & Lab Test Glossary
Plain-English definitions for 80+ common health, biomarker, and lab terms — everything you need to understand your results.
A
- Albumin
- A protein made by the liver that maintains blood volume and transports hormones, drugs, and nutrients.
- ALT (Alanine Aminotransferase)
- A liver enzyme that rises in the blood when liver cells are damaged or inflamed.
- Anemia
- A condition in which the blood lacks enough healthy red blood cells or hemoglobin to carry adequate oxygen to tissues.
- AST (Aspartate Aminotransferase)
- A liver and heart enzyme used alongside ALT to assess liver health and detect liver or muscle damage.
- ApoB (Apolipoprotein B)
- A protein that wraps every atherogenic lipoprotein particle; a strong predictor of cardiovascular disease risk.
B
- Basophils
- A type of white blood cell involved in allergic reactions and inflammation, normally present in very small numbers.
- Bilirubin
- A yellow pigment produced from red blood cell breakdown; elevated levels may indicate liver disease or hemolysis.
- Biomarker
- A measurable biological indicator — such as a blood protein, enzyme, or hormone — used to assess health status or disease risk.
- Blood Glucose
- The concentration of sugar (glucose) in the blood; the primary marker for diagnosing and monitoring diabetes.
- Blood Pressure
- The force exerted by circulating blood against artery walls, measured as systolic (peak) over diastolic (resting) pressure.
- Blood Urea Nitrogen (BUN)
- A measure of the amount of nitrogen in the blood from urea; used to evaluate kidney function.
- BMI (Body Mass Index)
- A screening index calculated from height and weight used to classify underweight, normal, overweight, and obese ranges.
C
- C-Peptide
- A byproduct of insulin production that helps distinguish between Type 1 and Type 2 diabetes and assess insulin secretion.
- Calcium
- A mineral in the blood essential for bone health, nerve signaling, muscle contraction, and cardiac function.
- Cholesterol (Total)
- The overall amount of cholesterol circulating in the blood, including LDL, HDL, and VLDL fractions.
- Cortisol
- A steroid hormone released by the adrenal glands in response to stress that regulates metabolism, immunity, and blood pressure.
- Creatinine
- A muscle metabolism waste product filtered by the kidneys; elevated levels signal reduced kidney function.
- CRP (C-Reactive Protein)
- An acute-phase protein produced by the liver in response to inflammation; elevated levels indicate systemic inflammation.
D
- DHEA-S
- An androgen precursor hormone produced by the adrenal glands that declines with age and is used to evaluate adrenal function.
E
- Eosinophils
- White blood cells that combat parasites and are elevated in allergic conditions and certain inflammatory diseases.
- Estimated GFR (eGFR)
- A calculated measure of how well the kidneys filter waste from the blood per minute, used to stage chronic kidney disease.
F
- Ferritin
- A protein that stores iron in cells; blood ferritin levels reflect the body's total iron stores.
- Fibrinogen
- A blood clotting protein made by the liver; elevated levels are associated with increased cardiovascular and stroke risk.
- Folate (Folic Acid)
- A B-vitamin essential for DNA synthesis, cell division, and red blood cell formation; critical during pregnancy.
- Free T3 (Triiodothyronine)
- The active, unbound form of the thyroid hormone T3 that directly regulates metabolism at the cellular level.
- Free T4 (Thyroxine)
- The unbound, active form of the thyroid hormone T4 that is converted to T3 in peripheral tissues.
- FSH (Follicle-Stimulating Hormone)
- A pituitary hormone that regulates reproductive function and is used to evaluate fertility and menopause status.
G
- GGT (Gamma-Glutamyl Transferase)
- A liver enzyme particularly sensitive to alcohol consumption and bile duct disease, used to assess liver health.
- Globulin
- A group of blood proteins made by the liver and immune system; the albumin-to-globulin ratio aids in diagnosing liver and immune disorders.
- Glucagon
- A pancreatic hormone that raises blood glucose by stimulating the liver to break down glycogen.
H
- HbA1c (Glycated Hemoglobin)
- A blood test reflecting average blood glucose levels over the past two to three months; the primary marker for diabetes management.
- Hematocrit
- The percentage of blood volume occupied by red blood cells; low values indicate anemia, high values may suggest dehydration or polycythemia.
- Hemoglobin
- The iron-containing protein in red blood cells that carries oxygen from the lungs to the rest of the body.
- HDL Cholesterol
- High-density lipoprotein cholesterol, often called "good" cholesterol because it transports excess cholesterol to the liver for removal.
- hsCRP (High-Sensitivity CRP)
- A highly sensitive assay of C-reactive protein used to detect low-grade chronic inflammation and assess cardiovascular risk.
- Homocysteine
- An amino acid produced during protein metabolism; elevated blood levels are linked to increased cardiovascular and stroke risk.
I
- IGF-1 (Insulin-Like Growth Factor 1)
- A hormone produced mainly by the liver in response to growth hormone; reflects GH activity and affects growth and metabolism.
- Insulin
- A pancreatic hormone that allows cells to absorb glucose from the blood; fasting insulin levels are used to assess insulin resistance.
- Iron (Serum)
- The concentration of iron circulating in the blood; used alongside ferritin and TIBC to diagnose iron deficiency or overload.
L
- LDL Cholesterol
- Low-density lipoprotein cholesterol, commonly called "bad" cholesterol because excess LDL contributes to arterial plaque buildup.
- LH (Luteinizing Hormone)
- A pituitary hormone that triggers ovulation in women and testosterone production in men; used in fertility assessments.
- Lymphocytes
- White blood cells that are the primary mediators of immune responses, including antibody production and targeted cell killing.
M
- Magnesium
- A mineral involved in over 300 enzymatic reactions, including energy production, muscle contraction, and nerve function.
- MCH (Mean Corpuscular Hemoglobin)
- The average amount of hemoglobin per red blood cell; used alongside MCV to classify types of anemia.
- MCHC (Mean Corpuscular Hemoglobin Concentration)
- The average concentration of hemoglobin within red blood cells; helps classify anemias.
- MCV (Mean Corpuscular Volume)
- The average size of red blood cells; abnormal values distinguish between different forms of anemia.
- Monocytes
- White blood cells that mature into macrophages and dendritic cells; they digest pathogens and help regulate immune responses.
N
- Neutrophils
- The most abundant white blood cell type, serving as the body's first line of defense against bacterial and fungal infections.
O
- Omega-3 Index
- A measure of EPA and DHA omega-3 fatty acids in red blood cell membranes, used to assess cardiovascular and inflammation risk.
P
- Phosphorus
- A mineral critical for bone formation, energy metabolism (ATP), and cell membrane structure.
- Platelets
- Small blood cells that clump together to form clots and stop bleeding; abnormal counts can indicate clotting disorders.
- Potassium
- An electrolyte essential for heart rhythm, muscle function, and fluid balance; monitored closely in kidney and heart disease.
- Prolactin
- A pituitary hormone that stimulates breast milk production and whose elevated levels can disrupt reproductive hormones.
- PSA (Prostate-Specific Antigen)
- A protein produced by the prostate gland; elevated blood levels may indicate prostate cancer, inflammation, or enlargement.
- PTH (Parathyroid Hormone)
- A hormone that regulates calcium and phosphorus levels in blood and bone; used to diagnose parathyroid and kidney disorders.
R
- RBC (Red Blood Cell Count)
- The number of red blood cells per volume of blood; used to diagnose anemia and polycythemia.
- RDW (Red Cell Distribution Width)
- A measure of the variation in red blood cell size; elevated values can indicate nutritional deficiencies or blood disorders.
- Reference Range
- The interval of test values expected in a healthy population, used as a benchmark to interpret individual laboratory results.
- Reticulocytes
- Immature red blood cells recently released from bone marrow; their count reflects the bone marrow's red cell production rate.
- Rheumatoid Factor (RF)
- An antibody found in the blood of many people with rheumatoid arthritis and some other autoimmune conditions.
S
- SHBG (Sex Hormone-Binding Globulin)
- A protein that binds sex hormones in the blood, regulating the amount of free testosterone and estradiol available to tissues.
- Sodium
- The primary electrolyte in blood and extracellular fluid, essential for fluid balance, nerve conduction, and blood pressure.
T
- Testosterone (Total)
- The total amount of the primary male sex hormone in the blood, encompassing both bound and free forms.
- Testosterone (Free)
- The small fraction of testosterone not bound to proteins, representing the biologically active portion available to tissues.
- TIBC (Total Iron-Binding Capacity)
- A measure of the blood's capacity to bind iron with transferrin; used to diagnose iron deficiency anemia.
- Thyroglobulin
- A protein produced by the thyroid gland used as a tumor marker to monitor thyroid cancer treatment and recurrence.
- TPO Antibodies (Thyroid Peroxidase)
- Autoantibodies that attack the thyroid enzyme TPO; elevated levels indicate autoimmune thyroid disease such as Hashimoto's.
- Transferrin
- The main protein that transports iron through the blood; levels are used to evaluate iron deficiency and liver function.
- Triglycerides
- Fats stored in the blood after eating; chronically elevated levels are a risk factor for cardiovascular disease and pancreatitis.
- TSH (Thyroid-Stimulating Hormone)
- A pituitary hormone that signals the thyroid to produce T3 and T4; the most sensitive primary screen for thyroid disorders.
U
- Uric Acid
- A waste product from purine metabolism; elevated blood levels (hyperuricemia) can cause gout and may signal kidney disease.
- Urinalysis
- A panel of urine tests evaluating appearance, concentration, and chemical composition to detect kidney, urinary, and metabolic conditions.
V
- Vitamin A
- A fat-soluble vitamin essential for vision, immune function, and cell growth; both deficiency and toxicity can be harmful.
- Vitamin B12
- A water-soluble vitamin required for nerve function, DNA synthesis, and red blood cell production; deficiency causes neurological damage.
- Vitamin C
- An antioxidant vitamin required for collagen synthesis, immune function, and iron absorption; deficiency causes scurvy.
- Vitamin D (25-OH)
- The storage form of vitamin D measured in blood to assess deficiency; supports bone health, immunity, and muscle function.
- Vitamin E
- A fat-soluble antioxidant that protects cell membranes from oxidative damage and supports immune function.
- Vitamin K
- A fat-soluble vitamin essential for blood clotting and bone metabolism, with two main forms: K1 (phylloquinone) and K2 (menaquinone).
W
- WBC (White Blood Cell Count)
- The total number of white blood cells per volume of blood; elevated or reduced counts signal infection, inflammation, or immune disorders.
Z
- Zinc
- A trace mineral essential for immune defense, wound healing, protein synthesis, and DNA production.
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