Reference Guide Only
This glossary is intended as a general educational reference. Test descriptions and reference ranges vary by laboratory. Always consult your healthcare provider for the meaning of your specific results.
The following alphabetical guide describes common laboratory tests ordered in outpatient and primary care settings. Each entry includes the test's full name, common abbreviation, and a brief description of what it measures and why it matters clinically.
Albumin ALB
Albumin is the most abundant protein in blood plasma, produced by the liver. It maintains oncotic pressure (keeping fluid inside blood vessels), transports hormones, drugs, and fatty acids, and serves as a marker of nutritional status and liver synthetic function. Low albumin levels may indicate malnutrition, liver disease, chronic inflammation, or kidney disease with protein loss.
Alanine Aminotransferase ALT
ALT is an enzyme found predominantly in liver cells. When liver cells are damaged or inflamed, ALT leaks into the bloodstream, causing measurable elevation. ALT is considered the more liver-specific of the two major liver enzymes (ALT and AST) and is a primary marker for hepatitis, fatty liver disease, medication-induced liver injury, and other forms of hepatocellular damage.
Alkaline Phosphatase ALP
ALP is an enzyme produced primarily in the liver, bile ducts, and bone. Elevated ALP most commonly reflects biliary obstruction, cholestatic liver disease, or increased bone turnover. Differentiating liver-derived from bone-derived ALP can be done using GGT: a simultaneously elevated GGT suggests liver or biliary origin, while a normal GGT with elevated ALP may suggest a bone condition such as Paget's disease or bone metastases.
Aspartate Aminotransferase AST
AST is found in the liver, heart, skeletal muscle, and red blood cells. It is elevated in liver disease and also in conditions affecting the heart muscle (myocardial infarction), skeletal muscle injury, or hemolysis. The AST-to-ALT ratio can help differentiate causes of liver disease: a ratio greater than two suggests alcoholic liver disease, while a ratio below one is more typical of viral hepatitis or non-alcoholic fatty liver disease.
Blood Urea Nitrogen BUN
BUN measures the concentration of urea nitrogen in the blood, a waste product formed from the breakdown of dietary protein and then filtered by the kidneys. Elevated BUN can result from impaired kidney function, dehydration, high protein intake, or gastrointestinal bleeding. BUN alone is less specific than the BUN-to-creatinine ratio, which helps differentiate pre-renal causes (dehydration) from intrinsic renal disease.
Calcium Ca
Calcium is a mineral critical for bone structure, muscle contraction, nerve transmission, and blood clotting. Serum calcium is tightly regulated by parathyroid hormone (PTH), vitamin D, and calcitonin. Hypercalcemia (high calcium) may suggest hyperparathyroidism, malignancy, or excessive vitamin D. Hypocalcemia (low calcium) may occur with hypoparathyroidism, vitamin D deficiency, or malabsorption. Total serum calcium must be corrected for albumin level for accurate interpretation.
Complete Blood Count CBC
The CBC is a panel that measures the cellular components of blood: red blood cell count and indices (hemoglobin, hematocrit, MCV, MCH, MCHC, RDW), white blood cell count with differential (neutrophils, lymphocytes, monocytes, eosinophils, basophils), and platelet count. It is used to screen for anemia, infection, bleeding disorders, and hematologic conditions.
C-Reactive Protein CRP / hs-CRP
CRP is an acute-phase protein produced by the liver in response to inflammation, infection, or tissue injury. Standard CRP detects significant elevations associated with acute illness. High-sensitivity CRP (hs-CRP) detects lower levels and is used for cardiovascular risk stratification. Persistently elevated hs-CRP is associated with higher risk of cardiovascular events independent of cholesterol levels.
Creatinine Cr / Creat
Creatinine is a waste product of muscle metabolism, filtered from the blood by the kidneys at a relatively constant rate in healthy individuals. Elevated serum creatinine reflects reduced kidney filtration capacity. Creatinine is used alongside BUN and eGFR to assess kidney function. Muscle mass significantly affects creatinine levels: athletes and muscular individuals may have higher baseline creatinine without kidney impairment.
Estimated Glomerular Filtration Rate eGFR
eGFR is a calculated value derived from serum creatinine, age, and sex that estimates how efficiently the kidneys are filtering blood. An eGFR of 90 or above is generally considered normal; values between 60 and 89 suggest mildly decreased kidney function; and values below 60 for more than three months indicate chronic kidney disease. The eGFR is the primary tool for staging kidney disease and monitoring progression.
Ferritin Ferritin
Ferritin is the primary iron storage protein in the body. Serum ferritin serves as an indirect measure of total body iron stores. Low ferritin is the earliest laboratory marker of iron deficiency, appearing before anemia develops. High ferritin can reflect iron overload (hereditary hemochromatosis), inflammation (since ferritin is an acute phase reactant), liver disease, or certain malignancies. Ferritin must be interpreted alongside other iron studies for complete assessment.
Fasting Glucose FG / Glucose
Fasting blood glucose measures blood sugar after a minimum eight-hour fast, reflecting baseline glucose levels without the influence of recent food intake. A fasting glucose below 100 mg/dL is normal; 100-125 mg/dL indicates impaired fasting glucose (prediabetes); and 126 mg/dL or above on two separate occasions meets the diagnostic threshold for diabetes mellitus. Fasting glucose is a component of the basic and comprehensive metabolic panels.
Hemoglobin A1c HbA1c
HbA1c reflects the percentage of hemoglobin molecules in red blood cells that have glucose attached, which corresponds to average blood glucose over the preceding two to three months. It does not require fasting and is used for diabetes screening and management monitoring. Conditions affecting red blood cell lifespan, such as hemolytic anemia or iron deficiency, can affect HbA1c accuracy.
HDL Cholesterol HDL-C
High-density lipoprotein (HDL) cholesterol facilitates the transport of excess cholesterol from peripheral tissues back to the liver for elimination. Higher HDL levels are associated with reduced cardiovascular risk. Low HDL is associated with metabolic syndrome, physical inactivity, smoking, obesity, and type 2 diabetes. HDL is measured as part of the standard lipid panel.
LDL Cholesterol LDL-C
Low-density lipoprotein (LDL) cholesterol is the primary carrier of cholesterol to peripheral tissues. Elevated LDL is strongly associated with the development of atherosclerosis and cardiovascular disease. LDL is typically calculated from other lipid panel values using the Friedewald equation or measured directly. Statin therapy targets LDL reduction in patients at elevated cardiovascular risk.
Potassium K
Potassium is the primary intracellular cation, essential for nerve impulse transmission, muscle contraction, and heart rhythm. Both hypokalemia (low potassium) and hyperkalemia (high potassium) can cause life-threatening cardiac arrhythmias. Potassium levels are closely monitored in patients with kidney disease, heart failure, and those taking diuretics, ACE inhibitors, or ARBs. Hemolyzed blood samples can produce falsely elevated potassium.
Sodium Na
Sodium is the primary extracellular cation and the major determinant of serum osmolality and fluid balance. Hyponatremia (low sodium) can result from excess water retention, heart failure, liver cirrhosis, or inappropriate antidiuretic hormone secretion. Hypernatremia (high sodium) typically reflects dehydration or water deficit. Sodium is always reported as part of the basic and comprehensive metabolic panels.
Thyroid-Stimulating Hormone TSH
TSH is produced by the pituitary gland to regulate thyroid hormone production. It is the most sensitive first-line test for thyroid dysfunction. An elevated TSH indicates the pituitary is working harder to stimulate an underactive thyroid (hypothyroidism). A suppressed TSH reflects either an overactive thyroid (hyperthyroidism) or excessive exogenous thyroid hormone. TSH testing is recommended every five years in adults over 35 and more frequently in those with symptoms or established thyroid disease.
Triglycerides TG / Trig
Triglycerides are the primary storage form of dietary fat. Elevated triglycerides (hypertriglyceridemia) are associated with cardiovascular risk, metabolic syndrome, and, at very high levels, pancreatitis. They are most accurately measured after a 9-12 hour fast, as a recent fatty meal can transiently elevate levels substantially. Factors contributing to high triglycerides include obesity, poorly controlled diabetes, alcohol use, and certain medications.
Uric Acid UA
Uric acid is the end product of purine metabolism. Elevated serum uric acid (hyperuricemia) can cause urate crystals to deposit in joints, resulting in gout. Chronic hyperuricemia is also associated with kidney stones and cardiovascular risk. Uric acid levels are influenced by diet (high purine foods such as red meat and shellfish), alcohol consumption, diuretic use, and kidney function. Uric acid monitoring is essential for patients being treated for gout or receiving urate-lowering therapy.