Correction formula for creatinine concentration with glucose in dialysate

Previous studies showed that high glucose in dialysate could interfere with creatinine measurement. This error might produce some mistakes in peritoneal dialysis (PD) treatment. The correction of creatinine is essentially needed.

Creatinine powder diluted in 0.1 N HCl was used as the standard reference. Different creatinine measurements obtained from unused dialysate solutions in various glucose concentrations were performed. Creatinine correction was performed by Twardowski's formula which was recommended by Nephrology Society of Thailand and by Tam's formula which utilized unused dialysate creatinine and glucose ratio. Comparison of the results in determination of membrane transport characteristics was based on the criteria proposed by Twardowski et al in used dialysate solutions derived from 17 CAPD patients with different approaches.

The mean creatinine concentrations obtained from the standard creatinine solution and the above two correction methods were different. The mean creatinine derived from Twardowski's formula was the lowest. The correlation coefficients between glucose and creatinine interference obtained by direct measurement and by Twardowski's formula were high (r = 0.80-0.98) at all creatinine levels. However, the correlation between glucose and creatinine interference were significant only at creatinine concentrations of 2.9 and 17.5 mg%. Classification of membrane transport was discordant when different correction formulae were used.

Creatinine correction in dialysate was crucial. Creatinine correction with fresh dialysate creatinine and glucose ratio might be suitable in clinical practice.