# Albumin, creatinine and cystatin C: what each test measures

Understand blood albumin, urine albumin, creatinine and cystatin C, including why kidney tests are read together.

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Published: 2026-07-15
Updated: 2026-09-30
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Creatinine and cystatin C help estimate how well the kidneys filter blood. Albumin answers a different question, and its meaning depends on whether it was measured in blood or urine. [1][2][3]

## 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?

## Sources
[1] Estimated Glomerular Filtration Rate Calculators - NIDDK (2024). https://www.niddk.nih.gov/health-information/professionals/clinical-tools-patient-management/kidney-disease/laboratory-evaluation/estimated-gfr-calculators
[2] Chronic Kidney Disease Tests & Diagnosis - NIDDK (2016). https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis
[3] Albumin Blood Test: MedlinePlus Medical Test (2024). https://medlineplus.gov/lab-tests/albumin-blood-test/
[4] Estimated GFR (eGFR) Test: Kidney Function Levels, Stages, and What to Do Next | National Kidney Foundation (2026). https://www.kidney.org/kidney-topics/estimated-glomerular-filtration-rate-egfr

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