Simultaneous inulin (Cin) and creatinine (Ccr) clearances were conducted on 53 pediatric renal patients employing a cimetidine protocol. Four 30-minute clearances were used. Cimetidine at 20 mg/kg per day, div BID, was administered for the two days preceding the studies and a diet free of meat, fish and fowl was used during the 24 hrs prior to the studies. There was near identity between the Cin and Ccr during the paired clearance periods (Table). In a clinical setting it is more practical to do a 2hrCcr than four, 30-minute collections. We combined the data from the four, 30-minute Ccr and calculated the 2hrCcr. The 2hrCcr very closely approximated the Cin.

Table 1
Full size table

The ratio of Ccr/Cin is not significantly different from 1.00. (In an earlier study of 39 children with simultaneous Cin and Ccr with no cimetidine, the Ccr/Cin = 1.36 ±.22.) The Bland-Altman graphic method for comparing two methods of clinical measurement shows that the 2hrCcr closely approximates the Cin with the latter ranging from 11 to 125 mL/min/1.73m2. Ccr measured using this cimetidine protocol with a two hour urine collection obtained under supervision in the clinic or office should closely approximate GFR measured using Cin.