Ambulatory GFR measurement with cold iothalamate in adults with chronic kidney disease.
BACKGROUND
The purpose of this study is to develop a method that eliminates the use of radioactive agents, reduces the length of inpatient visits, and does not require urine collection for the measurement of glomerular filtration rate (GFR) in adults with chronic kidney diseases (CKD).


METHODS
We measured simultaneous urinary and plasma clearance of iothalamate using high-performance liquid chromatography in 30 patients with CKD after a continuous subcutaneous infusion of iothalamate at a rate of 125 microL/h for a 24-hour period. To ascertain whether a steady state was achieved with a 24-hour infusion, in 20 additional patients, we infused iothalamate continuously for 48 hours and measured GFR after 24 and 48 hours.


RESULTS
Plasma iothalamate levels and urinary excretion rates obtained after 24- and 48-hour infusions were similar. GFR estimated by plasma clearance (44.4 mL/min; 95% confidence interval [CI], 37.0 to 53.3) was similar to urinary clearance (41.6 mL/min; 95% CI, 34.7 to 50.0) and without bias (average difference, 7%; 95% CI, +18% to -38%; P = 0.866). There also was acceptable agreement between plasma and urinary clearance of iothalamate (coefficient of variation [CV], 19.6% between techniques). Reproducibility of day-to-day plasma continuous infusion clearance technique was less than 12%. There was good agreement (CV, 19.9%) between inulin and renal iothalamate clearances.


CONCLUSIONS
These data show that ambulatory infusion of iothalamate can be used to measure GFR in adults with CKD without the need for urine collections with acceptable precision and without exposure to radioactivity.
Agarwal
Rajiv
R
Indiana University and Veterans Affairs Medical Center, Indianapolis, IN 46202, USA. ragarwal@iupui.edu
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000553:Ambulatory Care; D002851:Chromatography, High Pressure Liquid; D002908:Chronic Disease; D015897:Comorbidity; D005260:Female; D005919:Glomerular Filtration Rate; D006207:Half-Life; D006801:Humans; D015918:Infusion Pumps, Implantable; D007263:Infusions, Parenteral; D007444:Inulin / Q000032:analysis / Q000493:pharmacokinetics; D007483:Iothalamic Acid / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics; D007674:Kidney Diseases / Q000503:physiopathology*; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D015203:Reproducibility of Results
D007483:Iothalamic Acid; D007444:Inulin