12-hour versus 24-hour creatinine clearance in critically ill pediatric patients

Measurement of renal function is important to optimize drug dosing in critically ill pediatric patients and to prevent doserelated toxicities caused by medications that are eliminated or metabolized by the kidney. In clinical practice, the 24-h creatinine clearance (CrC1) is used as a surrogate marker of renal function. However, a 24-h urine collection period delays the availability of the result and increases the potential for collection errors. This prospective, observational study was performed to determine whether a 12-h CrC1 is comparable to the traditional 24-h CrC1 and to assess whether CrC1 could be reliably predicted by the Schwartz equation, which mathematically estimates a child's GFR. A 24-h urine sample was collected in two 12-h aliquots from 60 catheterized critically ill children (age 2 d to 18 y). CrC1 and Schwartz glomerular filtration rate (GFR) estimates were determined for each 12- and 24-h period. Agreement between 12- and 24-h CrC1 and between CrC1 and Schwartz GFR estimates was assessed using intraclass correlation coefficients (ICCs). An ICC >= 0.8 was considered to indicate excellent agreement. The ICC between the first 12-h CrC1 and 24-h CrC1 was 0.9605. The ICC between the second 12-h CrC1 and 24-h CrC1 was 0.9602. The ICC between the 24-h CrC1 and Schwartz GFR was only 0.7046. All comparisons of 12- and 24-h CrC1 indicated excellent agreement. In summary, the Schwartz equation was not a reliable estimate of renal function in critically ill children, and a 12-h CrC1 is just as accurate as the standard 24-h CrC1 to assess renal function and guide drug dosing.