[Validity of diagnostic methods for kidney function tests in the cat]

The diagnosis of kidney disease is difficult in the stage of compensation and impossible based solely on the routinely performed laboratory tests on blood and urine. For this reason, more sensitive methods are required. In the present study, three special techniques are compared with regard to their validity in the early diagnosis of kidney disease in the cat: 1. the molecular-weight related separation of urine proteins with the sodium-dodecyl-sulfate-polyacrylamide-gradient gel electrophoresis (SDS-page) in the PhastSystem, 2. measurement of the glomerular filtration rate (GFR) with the renalyzer PRX90 using an iodine containing contrast medium and 3. kidney scintigraphy. The results of this comparison demonstrate that these procedures are important adjuncts to common laboratory investigations in the testing of renal function. The SDS-page allows an early qualitative assessment on alterations of specific functional compartments of the kidney. However, it is not possible with this method alone to evaluate the degree of renal disturbance and it does not give information concerning the severity of renal functional impairment. Measurement of the GFR is also a valuable procedure which gives a quantitative result on the global renal function within a few hours. It is of special importance when subclinically disturbed kidney function is present. In the cat however it is until now not possible to give a correct prognosis in high grade nephropathies. Only scintigraphy allows unilateral assessment of renal function, which is most important in cats with morphologically altered kidneys, such as kidney cysts, hydronephrosis or tumours.