Test Details
Methodology
Turbidimetric (directly traceable to ERM-DA471/IFCC, the international standard reference material)
Result Turnaround Time
2 - 5 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Test Includes
Cystatin C; eGFR calculation
Use
Since it is formed at a constant rate and freely filtered by the healthy kidney, cystatin C is a good marker of renal function. Serum concentrations of cystatin C are almost totally dependent on glomerular filtration rate (GFR). A reduction in GFR causes a rise in the concentration of cystatin C.1,2
Can be used as a confirmatory test for the diagnosis of chronic kidney disease (CKD) in patients with a decreased GFR as estimated from creatinine.
Data suggests that 3.6% of U.S. adults would be classified as having CKD solely on the basis of a creatinine-based GFR estimate of 45 to 59 mL per minute per 1.73m2. A strategy of measuring cystatin C when the creatinine-based estimate is in this range and then reestimating GFR with the use of both these markers could correctly reclassify a substantial proportion of such patients as not having CKD and not being at high risk.
Can also be used to screen for CKD among persons who have a creatinine-based GFR estimate of 60 to 74 mL per minute per 1.73m2 without albuminuria (10.9% of US adults) or to obtain a more accurate estimation of GFR in patients with muscle wasting or chronic illness.
Limitations
Cystatin C has not been shown to be affected by factors such as muscle mass and nutrition, factors which have been demonstrated to affect creatinine values. In addition, a rise in creatinine does not become evident until the GFR has fallen by approximately 50%.
Custom Additional Information
The estimated glomerular filtration (GFR) provides an assessment of the filtering capacity of the kidney. The eGFR is calculated from a serum cystatin C using the CKD-EPI equation, 2012.3
Specimen Requirements
Specimen
Serum (preferred) or plasma
Volume
1 mL
Minimum Volume
0.5 mL
Container
Gel-barrier tube or green-top (heparin) tube
Collection Instructions
If green-top (heparin) tube is used, separate plasma from red blood cells and transfer plasma to a transfer tube.
Stability Requirements
| Temperature | Period |
|---|---|
| Room temperature | 7 days at 15°C to 25°C (stability provided by manufacturer or literature reference) |
| Refrigerated | 7 days at 2°C to 8°C (stability provided by manufacturer or literature reference) |
| Frozen | 6 months at -20°C (stability provided by manufacturer or literature reference) |
| Freeze/thaw cycles | Stable x1 (stability provided by manufacturer or literature reference) |
Storage Instructions
Room temperature
Patient Preparation
Overnight fasting is preferred.
Causes for Rejection
Specimen other than serum or heparinized plasma; grossly hemolyzed (>1,000 mg/dL Hgb) samples; excessive turbidity and clots in samples
References
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 121265 | Cystatin C with eGFR | 87430-5 | 121252 | Cystatin C | mg/L | 33863-2 |
| 121265 | Cystatin C with eGFR | 87430-5 | 121266 | eGFR | mL/min/1.73 | 50210-4 |
| Order Code | 121265 | |||||
| Order Code Name | Cystatin C with eGFR | |||||
| Order Loinc | 87430-5 | |||||
| Result Code | 121252 | |||||
| Result Code Name | Cystatin C | |||||
| UofM | mg/L | |||||
| Result LOINC | 33863-2 | |||||
| Order Code | 121265 | |||||
| Order Code Name | Cystatin C with eGFR | |||||
| Order Loinc | 87430-5 | |||||
| Result Code | 121266 | |||||
| Result Code Name | eGFR | |||||
| UofM | mL/min/1.73 | |||||
| Result LOINC | 50210-4 |