Determination of Kidney Function

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 a one of two plasma clearance

methods that does 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.

• Shemesh O, Golbetz H, Kriss JP, Myers BD. Limitations of creatinine as a filtration marker in glomerulopathic patients. Kidney Int. 1985 Nov;28(5):830-8.
• Bauer JH, Brooks CS, Burch RN. Clinical appraisal of creatinine clearance as a measurement of glomerular filtration rate. Am J Kidney Dis. 1982 Nov;2(3):337-46.
• Blythe WB. The endogenous creatinine clearance. Am J Kidney Dis. 1982 Nov;2(3):321-3. No abstract available.

• INCLUSION CRITERIA:

Ability to provide informed assent to all aspects of the study after full information is provided.

An indication to measure kidney function as accurately as possible in the context of an approved clinical protocol within the intramural programs of the National Institutes of Health:

• For minor subjects, a clinical indication will be required.
• For adult subjects, a clinical and/or research indication will be required.

EXCLUSION CRITERIA:

Pregnant females or nursing mothers will be excluded from all aspects of this study (at least until the infant is stable on a regimen of formula feeding).

Patients will not receive a test material if there is a history of allergy to that material.

Patients with a history of bronchial asthma or allergy to iodine-containing contrast material will not receive iothalamate.