title: Drawbacks of the constant-infusion technique for measurement of renal function.
abstract: We investigated the validity of the steady-state constant infusion method (CIM), in which quantitative urinary recovery and constant plasma concentrations of the solute infused are required. Successive 3-h clearances of inulin and p-aminohippuric acid (PAH) were determined for 27 h in 25 patients with renal disease. Results were compared with the standard method of bladder clearance (StM) and with a modified CIM (ModCIM). The 24-h urinary recovery was incomplete for both inulin and PAH. Mean 24-h ModCIM inulin clearance overestimated StM by 4.5 ml.min-1 x 1.73 m-2 (range 0-9, P < 0.001) independent of the extent of renal impairment and pointed to slow distribution and/or extrarenal clearance of inulin. For PAH, the difference between ModCIM and StM clearance was related to the average PAH clearance by ModCIM and StM (r = 0.78). Furthermore, neither plasma inulin nor PAH became completely constant, because of the circadian rhythm in renal function. In conclusion, the conditions of the steady-state CIM technique are not fulfilled, and the method is not suitable for accurate measurement of inulin and PAH clearance, especially when the clearance is low.
authors.affiliation: Department of Medicine, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: B A
authors.initials: BA
authors.lastname: Van Acker
authors.forename: G C
authors.initials: GC
authors.lastname: Koomen
authors.forename: L
authors.initials: L
authors.lastname: Arisz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002940:Circadian Rhythm; D005069:Evaluation Studies as Topic; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007444:Inulin / Q000097:blood / Q000652:urine; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D013997:Time Factors; D010130:p-Aminohippuric Acid / Q000097:blood / Q000652:urine
chemical_list: D007444:Inulin; D010130:p-Aminohippuric Acid