Validation of Fast Methods to Measure Glomerular Filtration Rate

This study will test the accuracy of a new "Fast GFR" (glomerular filtration rate) test to evaluate kidney function. Accurate assessment of kidney function is important in many clinical situations, including detecting kidney disease early, determining appropriate drug dosages, deciding when to begin dialysis, and evaluating heart and kidney organ donors and recipients. The current GFR test is used mostly for research purposes, as it is too costly and complicated for general medical use. Another significant drawback to its use in diagnosing acute kidney failure is the time it takes (3 to 24 hours) to complete, since effective therapy for this condition requires its detection as soon as possible. The Fast GFR, by comparison, takes only 45 minutes.

Patients 6 years old and older with kidney disease or with impaired kidney function caused by abnormal heart function or swelling-from congestive heart failure, severe infections, swelling from fluid accumulation, fluid in the abdomen, or burns-may be eligible for this study. Patients will undergo both the standard and the Fast GFR tests, described below, to evaluate the accuracy of the new test.

Fast GFR: Two catheters (thin flexible tubes) are placed into two arm veins, one for injecting iothalamate-an agent commonly used in CT scanning and blood vessel imaging-and the other for collecting blood samples. Baseline blood and urine samples are collected and then 0.5 milliliter (ml) iothalamate is injected into a vein. Blood samples are collected at 5, 10, 15, 20, 30, and 45 minutes in adults and at 5, 15, and 45 minutes in children. Urine is collected at 45 minutes. The size of the bladder is measured using ultrasound to determine if the bladder has completely emptied.

Standard GFR: Iothalamate (1 ml) is injected under the skin. Blood samples are collected at 60, 90, 120, 180 and 240 minutes. (A heparin lock is used to avoid multiple needle sticks.) Urine is collected at 60, 90, 120, 180 and 240 minutes. The size of the bladder is measured using ultrasound to determine if the bladder has completely emptied.