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Glomerular filtration rate measurement by "single-shot" injection of inulin
K W Florijn1, J N Barendregt, E G Lentjes
1Department of Nephrology, University Hospital Leiden, The Netherlands.
In 14 ADPKD patients the total body clearance and the urinary clearance of inulin using the constant infusion method were compared with the "single-shot" technique. Triplicate measurements of both clearances by each infusion method were obtained in 12 out of 14 patients. A high correlation was found between the total body clearance and the urinary clearance for both the constant infusion method (r = 0.96) and the single injection technique (r = 0.96). The coefficient of variation for the total body clearance of inulin was significantly lower for the constant infusion method and the single injection technique (7.8% and 7.1%) than for the urinary clearance of inulin (11.3% vs. 9.7%, P < 0.05). A constant overestimation of the urinary clearance by the total body clearance was observed with both methods (constant infusion method 8.3 ml.min-1 x 1.73 m-2 and single injection technique 13.4 ml.min-1 x 1.73 m-2). No concentration-dependent clearance was present. Determination of plasma inulin, especially at low levels, showed substantial interference by glucose. We conclude that, taking into account a constant overestimate of urinary clearance by the total body clearance of inulin, the single injection total body clearance possesses the best reproducibility and shows a good agreement with the conventional urinary clearance, which can be calculated by: GFR = TBCLss-13.1 ml.min-1 x 1.73 m-2 (in the range of 28 to 124 ml.min-1 x 1.73 m-2).
In 14 ADPKD patients the total body clearance and the urinary clearance of inulin using the constant infusion method were compared with the "single-shot" technique. Triplicate measurements of both clearances by each infusion method were obtained in 12 out of 14 patients. A high correlation was found between the total body clearance and the urinary clearance for both the constant infusion method (r = 0.96) and the single injection technique (r = 0.96). The coefficient of variation for the total body clearance of inulin was significantly lower for the constant infusion method and the single injection technique (7.8% and 7.1%) than for the urinary clearance of inulin (11.3% vs. 9.7%, P < 0.05). A constant overestimation of the urinary clearance by the total body clearance was observed with both methods (constant infusion method 8.3 ml.min-1 x 1.73 m-2 and single injection technique 13.4 ml.min-1 x 1.73 m-2). No concentration-dependent clearance was present. Determination of plasma inulin, especially at low levels, showed substantial interference by glucose. We conclude that, taking into account a constant overestimate of urinary clearance by the total body clearance of inulin, the single injection total body clearance possesses the best reproducibility and shows a good agreement with the conventional urinary clearance, which can be calculated by: GFR = TBCLss-13.1 ml.min-1 x 1.73 m-2 (in the range of 28 to 124 ml.min-1 x 1.73 m-2).