Creatinine: a starting point for estimating filtration
Creatinine is a waste product associated with normal muscle breakdown. The kidneys remove it from the blood. A laboratory can use blood creatinine in a formula to calculate estimated glomerular filtration rate, usually shortened to eGFR. That number estimates how well the kidneys filter.[2]
Muscle size and diet can affect creatinine levels and the resulting estimate.[4]
Cystatin C: another input for the estimate
Cystatin C is a protein that can also be measured in blood to estimate filtration. Combining it with creatinine generally produces a more accurate eGFR than using creatinine alone.[1][4]
NIDDK highlights the combined equation when an estimate is near a value that could change a clinical decision.[1]
Blood albumin and urine albumin are different tests
Blood albumin, sometimes called serum albumin, measures a protein made by the liver. It helps keep fluid inside blood vessels and carries substances through the bloodstream. A low result can have several explanations, including liver disease, kidney disease, infection or nutritional problems. High blood albumin can reflect dehydration. The result alone cannot identify the cause.[3]
Urine albumin looks for protein passing into urine. A urine albumin-to-creatinine ratio, or UACR, compares albumin with creatinine in the urine sample. It provides information about possible kidney damage alongside the blood-based filtration estimate. A blood albumin result does not substitute for UACR.[2]
What makes the results useful together
A kidney assessment can combine the filtration estimate, urine albumin and changes over time. Repeat testing may be needed to confirm urine albumin findings.[2][4]
Useful questions about a report are: Was albumin measured in blood or urine? Which inputs were used for eGFR? Is this result different from earlier measurements?
