How should creatinine and cystatin C be used together?
The KDIGO CKD 2013 guidelines recommended using eGFRcr as an initial test, followed by a confirmatory test for situations in which eGFRcr is thought to be inaccurate.
Confirmation of the level of GFR may also be appropriate for clinical decisions regarding medications toxicity, initiation of dialysis, or candidacy for kidney donation.
Confirmatory tests could include eGFRcr-cys or eGFRcys or a clearance measurement using either an exogenous filtration marker or a timed urine collection for creatinine clearance.
In general, eGFRcr-cys is more accurate than eGFRcys and should be used as the confirmatory test. However, in certain populations (e.g., patients with neuromuscular diseases, limb amputation, eating disorders), eGFRcys has been hypothesized to be more accurate than eGFRcr.
In states of pregnancy or rapidly changing kidney function, estimated GFR from cystatin C cannot be used and clearance measurements would be required.
eGFRcrcys, Estimated GFR from creatinine and cystatin; eGFRcr, estimated GFR from creatniine.Lists the Indications for an eGFRcrcys or Clearance Measurement Because eGFRcr May Be Inaccurate
- Extremes of age and body size
- Severe malnutrition or obesity
- Disease of skeletal muscle
- Paraplegia or quadriplegia
- Vegetarian diet
