Peritoneal equilibration test: Does glucose interfere with enzymatic creatinine measurement?

Peritoneal dialysis (PD) is a well-established treatment for patients with end-stage renal failure. Crucial to the success of PD is the peritoneal equilibration test (PET). The PET facilitates personalized PD regimens, allowing clinicians to optimize PD based on the peritoneal membrane transport performance of the individual patient.

The PET involves measurement of creatinine in serum and dialysate. Creatinine is most commonly measured by the compensated kinetic Jaffe method and, increasingly, by enzymatic methods. Positive glucose interference in Jaffe methods is well documented, ¹ and therefore is particularly relevant to PET given the high dextrose concentration of peritoneal dialysate. ² Formulae to correct for the interference of glucose in the Jaffe creatinine assay are widely used ³ and should be derived for each analyser method. ⁴

Data in the literature are contradictory on whether glucose does not interfere^2,4,5 or interferes positively^3,6 in PD fluid enzymatic creatinine measurement. Given these conflicting reports, we evaluated the effect of varying glucose concentrations in dialysis fluid on enzymatic creatinine analysis at different creatinine concentrations.

Aliquots of two PD fluids: Baxter Dianeal PD4 Glucose 2.27% (126.1 mmol/L) (Baxter Healthcare Corporation Newbury, Berkshire, UK) and Fresenius CAPD/DPCA Glucose 2.3% (126.1 mmol/L) (Fresenius Medical Care Deutschland GmbH, Bad Homburg, Germany) were diluted with deionized water to obtain five aliquots of each PD fluid with varying glucose concentrations. Creatinine (Sigma-Aldrich, Poole, UK) was spiked into each aliquot to obtain final calculated concentrations of 44 µmol/L and 484 µmol/L. Each unspiked (creatinine 0 µmol/L) and spiked aliquot was analysed in triplicate for creatinine (enzymatic) and glucose (hexokinase and glucose-6-phosphate dehydrogenase) using reagents supplied by Abbott diagnostics on the Abbott Architect c16000 analyser (Abbott Diagnostics, Abbott Park, IL, USA). Measured creatinine concentrations were plotted against measured glucose concentrations and compared against analytical imprecision derived from internal quality control results for creatinine (Figure 1).

OPEN IN VIEWER

Figure 1.

Creatinine concentrations (mean with SEM as error bars) versus increasing glucose concentration.

There was no significant effect of varying glucose concentrations on measured creatinine (Figure 1). Creatinine was below the detection limit (<8.8 µmol/L) in all unspiked aliquots.

In the PD fluids studied, there was no interference by glucose, for concentrations varying from 7.65 mmol/L to 143.2 mmol/L, in the Abbott Architect enzymatic creatinine assay (Figure 1). These data are consistent with studies reporting no glucose interference^2,4,5 but not those reporting interference.^3,6 Furthermore, we did not identify glucose interference at increasing creatinine concentrations as previously reported. ³ The difference in these reports may be related to enzymatic creatinine method, since those reporting interference used the Kodak Ektachem enzymatic creatinine method.^3,6 In conclusion, the Abbott Architect enzymatic creatinine method is free from glucose interference and may be used reliably to measure dialysate creatinine in the PET without need for correction formulae.