section name header

Introduction ⬇

Cystatin C is a low-molecular-weight protein inhibitor found in blood serum and is an indicator of glomerular filtration in kidney function.

This test is done to assess GFR. Cystatin C may be a more reliable indicator of kidney function than creatinine. Cystatin C is independent of muscle mass and age and is not reabsorbed in the kidney. Measurements of cystatin C are not as common as creatinine measurements.

Normal Findings ⬆ ⬇

Young adults: <0.70 mg/mL (<2.9 μmol/mL)

Older adults (older than 60 years): <0.85 mg/mL (<3.5 μmol/mL)

Procedure ⬆ ⬇

  1. No fasting is required.

  2. Obtain a 5-mL venous blood sample (heparin or EDTA).

Clinical Implications ⬆ ⬇

Cystatin C levels abnormally increase in association with impaired kidney function and loss of kidney homeostasis, as in acute kidney injury, CKD, diabetic nephropathy, and infections.

Interventions ⬆

Pretest Patient Care

  1. Explain purpose and sampling procedure for cystatin C.

  2. Assess for signs of abnormal kidney function (hypertension, pain, edema, uremia, disorders of urination, and urine composition). Some conditions have no symptoms of nephrotic syndrome.

  3. Follow Chapter 1 guidelines for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review outcomes and provide the patient with support and counseling.

  2. Explain follow-up testing and possible treatment for kidney disease.

  3. See Chapter 1 guidelines for safe, effective, informed posttest care.