title: Constant infusion clearance is an inappropriate method for accurate assessment of an impaired glomerular filtration rate.
abstract: Recently renewed interest has been focused on constant infusion clearance to assess GFR accurately. In this study we compared GFR and ERPF calculated from the constant infusion method (CIM = I x V/P) with that calculated from the standard method (StM = U x V/P), in 100 patients with renal disease who were subdivided in four groups according to their GFR-StM (< 30; 30-60; 60-90; > 90 ml/min). After a priming dose, a constant infusion of 125I-iothalamate (= GFR) and 131I-hippurate (= ERPF) was started at 9 a.m. The infusion rates were individually adjusted to the GFR which was approximated from the serum creatinine concentration. After a 90-min equilibration period, GFR-StM and ERPF-StM were determined for two 2-h periods. These values were compared with GFR-CIM and ERPF-CIM calculated from the plasma concentration of the respective tracers at the end of each 2-h period (= 210 and 330 min). In the patient group with GFR-StM < 30 ml/min, the 125I-iothalamate plasma concentration increased progressively over time. Consequently, average GFR-CIM at 210 min (34.2, SE +/- 2.1 ml/min) was higher than the GFR-CIM at 330 min (31.9, SE +/- 2.0 ml/min; P < 0.001). In addition both values were significantly higher than the corresponding GFR-StM values (18.1 +/- 2.4 and 15.3 +/- 1.6 ml/min respectively). In the two patient groups with GFR-StM > 60 ml/min, the 125I-iothalamate plasma concentration decreased progressively over time.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Internal Medicine, Free University Hospital, Amsterdam, The Netherlands.
authors.forename: C
authors.initials: C
authors.lastname: van Guldener
authors.forename: R O
authors.initials: RO
authors.lastname: Gans
authors.forename: P M
authors.initials: PM
authors.lastname: ter Wee
mesh_terms: D005919:Glomerular Filtration Rate / Q000502:physiology; D006626:Hippurates / Q000378:metabolism*; D006801:Humans; D007262:Infusions, Intravenous; D007457:Iodine Radioisotopes; D007483:Iothalamic Acid / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism*; D007674:Kidney Diseases / Q000378:metabolism* / Q000503:physiopathology; D012079:Renal Circulation; D012189:Retrospective Studies
chemical_list: D006626:Hippurates; D007457:Iodine Radioisotopes; D007483:Iothalamic Acid; C030514:hippuric acid