Kidney Function Test (Cystatin C)

On TestWell the Kidney Function Test (Cystatin C) is $36.99. Quest Direct lists cystatin C at $60, and hospital labs typically charge around $180 for the same draw without insurance. Same CLIA-certified labs, same biomarker — TestWell removes the facility markup.

A cystatin C test is a blood draw that measures a small protein your body produces at a steady rate. Healthy kidneys filter it out efficiently; when kidney function declines, cystatin C builds up in the blood. The result is used to calculate an eGFR (estimated glomerular filtration rate) that reflects how well your kidneys are filtering waste.

Creatinine is a byproduct of muscle metabolism, so levels vary with muscle mass, diet, and body size — a muscular person can have high creatinine with perfectly healthy kidneys, while a frail older adult may have normal creatinine despite significant kidney decline. Cystatin C is produced at a constant rate by nearly every cell in the body and is not influenced by these factors, making it a more reliable marker across diverse body types.

No fasting is required. You can eat and drink normally before the blood draw. If you're pairing this test with other panels that do require fasting, check the prep instructions for those specific tests.

The CPT code for cystatin C is 82610. Cash-pay patients ordering through TestWell do not need to supply a CPT code — it's handled on the lab requisition automatically.

A Renal Panel includes creatinine, BUN, electrolytes, and other kidney and metabolic markers — it gives a broad snapshot of kidney and fluid balance. The Cystatin C test focuses specifically on one highly accurate filtration marker and its derived eGFR, making it the better choice when you need to confirm or clarify a borderline creatinine result or get the most precise eGFR possible.

Yes. After ordering on TestWell, you'll receive a digital lab requisition you can take to any Quest Diagnostics or LabCorp patient service center. Both networks have thousands of walk-in locations nationwide, so you can choose whichever is most convenient.

Testing frequency depends on your situation and should be guided by your provider. As a general reference, people with known chronic kidney disease are often monitored every 3–6 months; those screening for early decline with risk factors may test once or twice a year. If this is a one-time confirmation of a borderline creatinine result, a single test may be sufficient until your clinical picture changes.

Kidney Function Test (Cystatin C) results are typically ready in 2–4 business days after your draw at Quest or Labcorp. TestWell emails you the moment they post, and your results dashboard shows each marker against its reference range with a plain-English explanation.

Dehydration, creatine supplements and ibuprofen and other NSAIDs can change a Kidney Function Test (Cystatin C) result without anything being wrong. Dehydration can lower eGFR — repeat well-hydrated before acting on a low eGFR. Creatine supplements can falsely lower eGFR — do not accept a 'stage 2/3 CKD' label on creatinine alone while on creatine — confirm with cystatin C. Ibuprofen and other NSAIDs can lower eGFR — A low eGFR on daily NSAIDs plus dehydration is repeated off both before it is labelled kidney disease. Each factor is covered on our physician-reviewed "Before your test" pages; when one applies, the fix is usually to remove it and retest.

The Kidney Function Test (Cystatin C) is Quest Diagnostics test code 94588 ("Cystatin C with Glomerular Filtration Rate, Estimated (eGFR)"), Labcorp test number 121265 ("Cystatin C with eGFR"), BioReference code J013-4 (CPT 82610). TestWell orders it under those codes for $36.99 at Quest, Labcorp or BioReference — no doctor's visit or insurance required, results in 2–4 business days. Codes verified against the labs' catalogs in 2026.