Determination of Kidney Function

Overview

Much more about kidney disorders can be learned by determining kidney function. This research proposes to study the kidneys function by several parameters known as glomerular filtration rate (GFR), Renal Plasma Flow (RPF), and Glomerular Capillary Wall Permselectivity. The study will select patients suffering from different types of kidney diseases. These patients will be selected based on the presence of significant amounts of protein in their urine (proteinuria). Standard blood and urine tests are often unable to provide completely accurate information about the kidney. In order for researchers to have a more accurate idea of kidney function, they will use alternative tests. Test materials (para aminohippurate and inulin) will be injected into patients veins that provides information based on their filtration through the kidneys....

The study of various kidney disorders will be facilitated by determinations of true glomerular filtration rate and/or effective renal plasma flow employing inulin or non-radioactive iothalamate and/or para aminohippurate (PAH), respectively. Selected patients with proteinuria will be asked to participate in studies of glomerular capillary wall permselectivity calculated from the fractional clearances of the endogenous proteins, albumin and IgG and from the fractional clearances of polydisperse neutral dextran with effective molecular radii ranging from 20-60 angstroms. To achieve this, low molecular weight dextran will be administered by slow IV injection immediately following the inulin or iothalamate and/or PAH priming doses. Glomerular filtration rate, effective renal plasma flow and/or glomerular permselectivity can be measured simultaneously during a standard hydrated urinary clearance study. Timed urine and blood collections will be obtained, typically requiring a total of 60 to 90 minutes. The total test time, including pre-test hydration, is 4 to 5 hours. Alternatively, glomerular filtration rate can be measured by one of two plasma clearance methods that do not require urine collections. For one method, a steady-state plasma concentration of iothalamate will be achieved in ambulatory patients by a 24-hour subcutaneous infusion of iothalamate using an insulin pump. For the second method, the decline in plasma concentration of iothalamate will be measured after an intravenous dose of iothalamate.