Lab Tests Reference Library

Hemoglobin is the protein in red blood cells that carries oxygen throughout the body. It is the primary test for diagnosing anemia.

RBC count measures the number of red blood cells per volume of blood. Low RBC indicates anemia; high RBC (polycythemia) can suggest dehydration or bone marrow disorders.

WBC count measures the total number of white blood cells (leukocytes). Elevated WBC suggests infection or inflammation; low WBC may indicate bone marrow suppression.

Platelets (thrombocytes) are cell fragments essential for blood clotting. Low platelets (thrombocytopenia) cause bleeding risk; high platelets may suggest inflammation or clotting risk.

Hematocrit (packed cell volume) is the percentage of blood volume occupied by red blood cells. It reflects the overall red cell mass.

MCV measures the average size of red blood cells. Low MCV (microcytic) suggests iron deficiency or thalassemia; high MCV (macrocytic) suggests B12/folate deficiency.

MCH measures the average amount of hemoglobin per red blood cell. Low MCH indicates hypochromic (pale) red cells, typical of iron deficiency.

MCHC measures the average concentration of hemoglobin in red blood cells. Low MCHC confirms hypochromic anemia; high MCHC can suggest hereditary spherocytosis.

RDW measures the variation in red blood cell size (anisocytosis). Elevated RDW is an early marker of iron deficiency anemia and helps differentiate anemia types.

Neutrophils are the most abundant white blood cells and the first responders to bacterial infections. Elevated neutrophils suggest bacterial infection or stress; low levels (neutropenia) increase infection risk.

Lymphocytes are white blood cells critical for immune response. Elevated lymphocytes suggest viral infection; lymphocytopenia may indicate immune deficiency or steroid use.

Monocytes are white blood cells that mature into macrophages and dendritic cells. Elevated monocytes may suggest chronic infection, autoimmune disease, or inflammatory conditions.

Eosinophils fight parasites and participate in allergic reactions. Elevated eosinophils (eosinophilia) suggest allergies, asthma, or parasitic infections.

Basophils are the rarest white blood cells, involved in allergic reactions and inflammation. Elevated basophils may suggest allergic disease or myeloproliferative disorders.

ESR measures how quickly red blood cells settle in a test tube. It is a non-specific marker of inflammation and infection. Elevated ESR suggests ongoing inflammation.

CRP is a protein produced by the liver in response to inflammation. It rises rapidly during infection or inflammatory states. High-sensitivity CRP (hs-CRP) assesses cardiovascular risk.

PT measures how long it takes blood to clot via the extrinsic pathway. INR standardizes PT results globally. Used to monitor warfarin therapy and assess liver function.

aPTT measures clotting via the intrinsic pathway. Used to monitor heparin therapy and detect clotting factor deficiencies. Prolonged aPTT suggests coagulation disorders.

ALT is a liver enzyme that leaks into the blood when liver cells are damaged. It is the most specific marker for liver damage, elevated in hepatitis, fatty liver, and drug-induced liver injury.

AST is found in liver, heart, and muscle cells. Elevated AST suggests liver damage, heart attack, or muscle injury. AST:ALT ratio helps differentiate alcoholic vs non-alcoholic liver disease.

ALP is an enzyme found in liver, bone, kidneys, and intestines. Elevated ALP suggests bile duct obstruction, bone disorders, or liver disease.

GGT is an enzyme primarily found in the liver. Elevated GGT is sensitive for liver and bile duct disease and is a marker for excessive alcohol consumption.

Bilirubin is a breakdown product of hemoglobin. Elevated total bilirubin causes jaundice and indicates liver disease, bile duct obstruction, or increased red cell destruction (hemolysis).

Albumin is the main protein made by the liver. Low albumin (hypoalbuminemia) indicates chronic liver disease, malnutrition, or kidney protein loss.

Creatinine is a waste product from muscle metabolism filtered by the kidneys. Elevated creatinine indicates impaired kidney function.

BUN measures the amount of nitrogen from urea in blood. Elevated BUN can indicate kidney disease, dehydration, high protein diet, or GI bleeding.

eGFR estimates how well kidneys filter waste from blood. It is calculated from creatinine, age, and sex. eGFR <60 for 3+ months defines chronic kidney disease (CKD).

Uric acid is a breakdown product of purines. Elevated uric acid (hyperuricemia) causes gout and kidney stones. Low levels may suggest certain genetic disorders.

Sodium is the primary extracellular electrolyte controlling fluid balance. Abnormal sodium causes neurological symptoms. Critical for cardiac and brain function.

Potassium is essential for heart rhythm, muscle contraction, and nerve function. Both low (hypokalemia) and high (hyperkalemia) levels are potentially life-threatening.

Chloride is the main extracellular anion, essential for fluid and acid-base balance. Usually measured as part of electrolyte panels.

Fasting blood glucose is measured after at least 8 hours of fasting. It is the primary test for diagnosing diabetes and pre-diabetes.

HbA1c reflects average blood glucose over the past 2–3 months. It is the gold standard for diabetes monitoring and diagnosis. Each 1% increase above 6.5% significantly increases complication risk.

Total cholesterol is the sum of all cholesterol types in blood. Elevated total cholesterol increases cardiovascular disease risk.

LDL ("bad" cholesterol) deposits on artery walls causing atherosclerosis. Lowering LDL is the primary target of cardiovascular risk reduction therapy.

HDL ("good" cholesterol) removes cholesterol from arteries and transports it to the liver. Higher HDL levels are protective against heart disease.

Triglycerides are fats stored in fat cells and carried in blood. Elevated triglycerides increase pancreatitis and cardiovascular risk, often linked to diabetes and obesity.

Troponin is released from heart muscle cells when they are damaged. It is the most specific marker for myocardial infarction (heart attack). High-sensitivity troponin detects minor heart damage.

CK-MB is a heart-specific form of creatine kinase. Elevated CK-MB suggests heart muscle damage. Used alongside troponin for diagnosis of myocardial infarction.

TSH is secreted by the pituitary gland to control thyroid hormone production. It is the single most sensitive test for thyroid dysfunction. High TSH = hypothyroidism; low TSH = hyperthyroidism.

Free T4 is the active, unbound form of thyroxine. Low Free T4 with high TSH confirms hypothyroidism; high Free T4 with low TSH confirms hyperthyroidism.

Free T3 is the most biologically active thyroid hormone. It is useful in diagnosing T3 toxicosis and monitoring thyroid replacement therapy.

Anti-TPO antibodies attack the thyroid gland. Elevated levels indicate autoimmune thyroid disease — primarily Hashimoto's thyroiditis or Graves' disease.

FSH regulates reproductive processes. In women it stimulates ovarian follicle development; in men it stimulates sperm production. Used in fertility evaluation and menopause diagnosis.

LH triggers ovulation in women and testosterone production in men. The LH surge signals the best time for conception. Elevated LH in women may indicate PCOS or premature ovarian failure.

Prolactin is produced by the pituitary gland and stimulates breast milk production. Elevated prolactin (hyperprolactinemia) causes irregular periods, infertility, and galactorrhea.

Testosterone is the primary male sex hormone. In men, low testosterone (hypogonadism) causes fatigue, reduced libido, and muscle loss. In women, high testosterone may suggest PCOS or adrenal disorders.

Estradiol is the primary female sex hormone. Used to evaluate ovarian function, fertility, menopause, and hormonal disorders in both men and women.

Cortisol is the primary stress hormone produced by the adrenal glands. Elevated cortisol may indicate Cushing's syndrome; low cortisol may indicate Addison's disease.

AMH reflects ovarian reserve — the remaining egg supply. Used in fertility assessment and IVF planning. Low AMH indicates diminished ovarian reserve.

25-hydroxy Vitamin D is the best test to measure Vitamin D status. Deficiency is extremely common globally and linked to bone disease, immune dysfunction, depression, and cardiovascular disease.

Vitamin B12 is essential for nerve function, DNA synthesis, and red blood cell formation. Deficiency causes macrocytic anemia, peripheral neuropathy, and cognitive impairment. Common in vegans and elderly.

Folate is a B vitamin essential for DNA synthesis and cell division. Deficiency causes macrocytic anemia and, in pregnancy, neural tube defects. Critical during first trimester of pregnancy.

Ferritin is the main iron storage protein and the best indicator of total body iron stores. Low ferritin is the earliest marker of iron deficiency, even before anemia develops.

Serum iron measures iron circulating in the blood. Used alongside TIBC and ferritin to fully assess iron status.

TIBC measures the blood's capacity to bind iron with transferrin. Elevated TIBC with low ferritin confirms iron deficiency anemia.

Calcium is essential for bone structure, muscle contraction, nerve function, and blood clotting. Abnormal calcium levels can cause severe symptoms affecting the heart and nervous system.

Magnesium is involved in hundreds of enzymatic reactions including energy production, protein synthesis, and muscle/nerve function. Deficiency is common and linked to cardiovascular disease, diabetes, and migraines.

Zinc is essential for immune function, wound healing, DNA synthesis, and taste/smell sensation. Deficiency impairs immunity and growth, especially in children.

ANA is a screening test for autoimmune diseases. A positive ANA indicates the immune system is producing antibodies against the body's own cells. Found in Lupus (SLE), Sjögren's, and other autoimmune conditions.

Anti-dsDNA antibodies are highly specific for Systemic Lupus Erythematosus (SLE/Lupus). Rising levels often correlate with lupus flares and kidney involvement.

Rheumatoid Factor is an antibody found in rheumatoid arthritis and other autoimmune conditions. A positive RF combined with joint symptoms supports the diagnosis of RA.

Anti-CCP (anti-cyclic citrullinated peptide) antibodies are highly specific for Rheumatoid Arthritis. More specific than RF and can be positive years before symptoms appear.

C3 is the most abundant complement protein. Low C3 suggests complement consumption in active autoimmune disease (especially lupus nephritis) or genetic C3 deficiency.

C4 is a complement protein involved in immune complex clearance. Low C4 with low C3 strongly suggests active lupus. C4 can also be low in hereditary angioedema.

IgG is the most abundant immunoglobulin, providing long-term immunity. Low IgG indicates immune deficiency; high IgG may suggest chronic infection, autoimmune disease, or multiple myeloma.

Total IgE is elevated in allergic conditions (asthma, atopic dermatitis, hay fever) and parasitic infections. Very high IgE can also suggest hyperIgE syndrome.

HBsAg is the first marker to appear in Hepatitis B infection. A positive result indicates active Hepatitis B infection (acute or chronic). Screening recommended for all adults at risk.

Anti-HBs indicates immunity to Hepatitis B — either from vaccination or recovery from infection. A level ≥10 IU/L is considered protective immunity.

Anti-HCV detects antibodies against Hepatitis C virus. A positive result requires confirmation with HCV RNA PCR. Hepatitis C can cause chronic liver disease, cirrhosis, and liver cancer.

Fourth-generation HIV test detecting both HIV-1/2 antibodies and p24 antigen. Detects HIV infection as early as 18 days post-exposure. Requires confirmatory testing if reactive.

CD4 count monitors immune function in HIV-positive patients. CD4 <200 cells/µL defines AIDS. Used to guide antiretroviral therapy initiation and prophylaxis decisions.

NS1 antigen is detectable in the first 1–5 days of dengue fever. It is an early marker that helps distinguish dengue from other febrile illnesses during the acute phase.

Dengue IgM appears 4–5 days after symptom onset and persists for 2–3 months. A positive IgM indicates recent dengue infection.

The Widal test detects antibodies against Salmonella typhi antigens. A fourfold rise in titer is significant. Used widely in endemic areas but has limitations in sensitivity/specificity.

Malaria RDT detects Plasmodium antigens in blood. Provides rapid diagnosis in endemic areas. Detects P. falciparum (most dangerous) and other species.

Urine pH measures the acidity or alkalinity of urine. It helps evaluate kidney stone risk, acid-base balance, and urinary tract infections. Alkaline urine may suggest UTI with urease-producing bacteria.

Proteinuria indicates kidney damage. Trace amounts may be normal or due to fever/exercise. Persistent proteinuria requires further evaluation with albumin/creatinine ratio. Associated with diabetic nephropathy, hypertensive kidney disease.

Glucose in urine (glucosuria) typically indicates blood glucose exceeding the renal threshold (~180 mg/dL). Seen in uncontrolled diabetes. Also occurs in renal glycosuria where glucose leaks at normal blood sugar levels.

Ketonuria indicates fat breakdown as an energy source. Present in diabetic ketoacidosis (DKA), starvation, low-carbohydrate diets, and prolonged vomiting. DKA is a medical emergency requiring urgent care.

Blood in urine (hematuria) can be gross (visible) or microscopic. Causes include kidney stones, UTI, glomerulonephritis, or bladder/kidney cancer. Any unexplained hematuria requires investigation.

Positive urine nitrites indicate bacterial infection. Gram-negative bacteria (E. coli, Klebsiella) convert dietary nitrates to nitrites. Combined with positive leukocytes, strongly suggests urinary tract infection (UTI).

White blood cells in urine (pyuria) indicate inflammation or infection of the urinary tract. Present in UTI, pyelonephritis, kidney stones, and interstitial nephritis. Combined with nitrites confirms bacterial UTI.

ACR is the preferred test to detect early diabetic kidney disease (microalbuminuria). It corrects for urine concentration. Persistently elevated ACR is an independent risk factor for cardiovascular events and kidney disease progression.

Specific gravity measures urine concentration. Low values suggest dilute urine (diabetes insipidus, excessive fluid intake, kidney disease). High values indicate concentrated urine (dehydration, SIADH, proteinuria).

24-hour urine protein quantifies daily protein excretion. It is the gold standard for evaluating nephrotic syndrome and monitoring kidney disease progression. >3.5 g/day defines nephrotic-range proteinuria.