Parameters to consider:
(1) approximate GFR in mL per min per 1.73 square meters BSA
(2) age of the patient
(3) body mass index (BMI)
(4) presence of the nephrotic syndrome
(5) presence of acute kidney injury
Indications for using serum cystatin C:
(1) estimated GFR 60 to 90 mL per min per 1.73 square meters BSA
(2) BMI > 30 kg per square meter
(3) nephrotic syndrome
(4) acute kidney injury
If the estimated GFR is < 20 mL per kg per 1.73 square meters BSA then use the average of the creatinine and urea clearances.
If none of the above apply, then use serum creatinine in one of the following equations:
(1) for an adult: Cockcroft-Gault or MDRD equation
(2) for a pediatric patient: Schwartz equation
