Biomarkers
Biomarkers: the individual substances the tests measure. Each page explains what the marker is, which organ makes or clears it, why a result may be higher or lower and what can distort it. Reference intervals belong to the laboratory that ran the test; nothing here interprets an individual result.
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A
Albumin
The most abundant protein in blood, made by the liver. It keeps fluid inside the vessels and carries hormones, drugs, calcium and bilirubin. A low level is…
ALP (alkaline phosphatase)
An enzyme made mainly by the cells lining the bile ducts and by bone-forming cells. A raised level with a raised GGT points to obstructed bile flow…
ALT (alanine aminotransferase)
An enzyme concentrated in liver cells that leaks into blood when they are injured. The most liver-specific of the routine liver blood tests and the one that…
AST (aspartate aminotransferase)
An enzyme found in liver cells but also in heart, skeletal muscle, kidney, brain and red cells. It rises with liver injury alongside ALT, and the AST:ALT ratio…
B
Bilirubin
The yellow pigment made when old red cells are broken down, processed by the liver and excreted in bile. A high level causes jaundice; whether the excess is…
Blood glucose
The concentration of glucose, the body's main circulating fuel, in blood at the moment of sampling. Kept within narrow limits by insulin and glucagon, it rises…
C
C-reactive protein (CRP)
A protein the liver pours into blood within hours of any significant inflammation, infection or tissue injury. It rises and falls fast, so it tracks the course…
Cardiac troponin
A protein of the contractile apparatus of heart muscle cells that leaks into blood when those cells are injured. High-sensitivity troponin is the blood marker…
Creatinine
A waste product of muscle metabolism produced at a steady rate and cleared almost entirely by the kidneys. The rise in blood creatinine when filtration falls…
E
F
Ferritin
The protein that stores iron inside cells; the small amount in blood mirrors the body's iron reserve. A low ferritin is the most reliable single sign of iron…
Folate
The B vitamin from green vegetables and fortified foods that cells need to make DNA; deficiency causes anaemia with large red cells and, in early pregnancy,…
Free T4 (thyroxine)
The unbound fraction of thyroxine, the main hormone the thyroid gland secretes. Measured with TSH, it tells whether a thyroid problem is mild or severe and…
G
H
Haematocrit
The fraction of blood volume made up of red cells, reported as a percentage or a ratio. It tracks haemoglobin closely and is part of every full blood count.
Haemoglobin
The iron-containing protein inside red blood cells that carries oxygen from the lungs to every tissue. Its concentration is the standard measure of anaemia and…
HbA1c (glycated haemoglobin)
Haemoglobin that has glucose attached to it. Because red cells live about three months, the HbA1c fraction reports average blood glucose over the previous two…
HDL cholesterol
The cholesterol carried by high-density lipoprotein, the particle that collects cholesterol from tissues and artery walls and returns it to the liver. A higher…
I
L
LDL cholesterol
The cholesterol carried by low-density lipoprotein, the particle that deposits cholesterol in artery walls and drives atherosclerosis. The main target of…
Lymphocytes
The white blood cells of adaptive immunity: B cells that make antibodies, T cells that direct the response and kill infected cells, and natural killer cells.…
M
N
Natriuretic peptides (BNP and NT-proBNP)
Hormones released by the heart's ventricles when their walls are stretched by high pressure or volume. A normal level makes heart failure unlikely; a high…
Neutrophils
The most numerous white blood cell and the first responder to bacterial infection. The absolute neutrophil count from the differential is the number clinicians…
P
Platelets
Small cell fragments that plug damaged vessel walls and start the clotting cascade. Too few (thrombocytopenia) and the person bruises and bleeds; too many…
Potassium
The main positively charged ion inside cells; only about 2% is in the blood, but that small fraction sets the electrical excitability of nerves, muscle and…
S
T
Total cholesterol
The sum of all the cholesterol carried in blood by lipoproteins: LDL, HDL and the remainder. One line of a lipid profile, useful mainly as the starting point…
Triglycerides
The main form in which fat is stored and transported: three fatty acids on a glycerol backbone, carried in blood by chylomicrons after meals and by VLDL from…
TSH (thyroid-stimulating hormone)
The pituitary hormone that drives the thyroid gland. Because the pituitary responds to tiny changes in thyroid hormone, TSH moves in the opposite direction to…