Understand kidney markers in your lab result

Creatinine is a waste product from normal muscle metabolism, filtered by the kidneys and excreted in urine. Blood creatinine levels reflect how well the kidneys are filtering waste.

BUN measures urea nitrogen in the blood, a waste product from protein metabolism. The kidneys filter urea from the blood; elevated BUN can indicate reduced kidney filtering or increased protein breakdown.

eGFR estimates how many millilitres of blood the kidneys filter per minute. It is calculated from serum creatinine, age, sex, and sometimes race, providing a standardised measure of kidney function.

Uric acid is produced when the body breaks down purines, compounds found in certain foods and in the body's own cell turnover. The kidneys excrete most uric acid in urine.

Cystatin C is a small protein produced at a steady rate by most cells in the body. Because the kidneys filter it out, the level in blood reflects how well filtration is working — and unlike creatinine, it is not strongly affected by muscle mass. It is read alongside creatinine, eGFR, BUN, electrolytes and urine albumin.

Urea is the waste molecule formed when the liver breaks down protein. The kidneys filter it from blood, so the level reflects both protein turnover and kidney filtration.

The BUN/creatinine ratio compares blood urea nitrogen to creatinine. It is a calculated value, not a directly measured one, and is most useful when read together with the individual BUN and creatinine results.