Measurement of glomerular filtration rate by rapid intravenous injection of a newly developed inulin fraction

Abstract

Objective: Since the conventional drip-infusion method for measuring inulin clearance (Cin) has problems related to its accuracy and performance, we explored a more accurate and concise method by rapid intravenous injection of a newly developed inulin fraction (Inulead(®)), in which spot urine sampling was omitted and the administration period of inulin was shortened from 120 to 5 minutes.

Patients and methods: Twenty seven patients (M/F: 15/12, 67.8 ± 12.9 years old) admitted to the Nephrology ward were enrolled in this study. Inulead(®), 1500 mg dissolved in 150 mL of saline, was intravenously administered in 5 minutes. Then, sequential blood samplings and urine collection were performed for 24 hours. Cins were calculated by the following three formulae: (1) a pharmacokinetic analysis using a two compartments model based on the plasma inulin concentration to determine Cin, which was the administered dose divided by the area under the curve (AUC) from 0 to ∞, (2) urinary inulin excretion divided by the AUC for 24 hours and (3) the Bayesian method using a three-point set of plasma inulin concentrations to predict the change of inulin concentration to determine Cin as in 1. These Cins were compared with levels of estimated GFR (eGFR), creatinine clearance (Ccr), serum β2 microglobulin (β2MG) and serum cystatin C (Cys C).

Results: Cins obtained by the above three methods were well correlated with each other (r. = 0.9088 (- )0.9998) and with eGFR (r. = 0.8286 - 0.8650), Ccr (r. = 0.821 - 0.864), 1/β2MG (r. = 0.631 - 0.752) and 1/CysC (r. = 0.830 - 0.857). The averaged differences of each Cin from eGFR were distributed between - 4.4 and - 4.5 mL/min.

Conclusion: Since the Cins by rapid inulin injection showed satisfactory correlation and differences with other GFR parameters, this method will be a good alternative to the drip infusion method, and may reduce the burden of patients and medical staff.

Keywords: Area Under the Curve (AUC); Bayesian method; Chronic Kidney Disease (CKD); Inulead; inulin clearance.

Figure 1

Correlation of PKCin, Uin/AUC, Cin-BM, and eGFR.

Figure 2

Bland-Altman plots of PKCin, Cin-BM, Uin/AUC, and eGFR. The mean ± SD of the difference between each Cin and eGFR is presented in the upper right corner. Open cirle: The case in first remission of minimal change nephritic syndrome showed a big difference between Cins and eGFR.