[Kidney function tests in horses--methods and reference values in healthy animals].

Investigations of renal function have been done on the basis of renal clearance (Clr) and excretion (E) of endogenous creatinine in healthy horses of different body weight (23 female, 7 male). Creatinine was measured by enzymatic PAP-method. Creatinine-E of female horses was poor positively correlated with body weight. The creatinine-Clr was highly correlated with the inulin-Clr (r = 0,896, p < 0,001). The excretion of creatinine was 35% higher than the filtration of creatinine, determined by inulin-Clr. That demonstrate a tubular net secretion of 26% of the total creatinine excretion. However the creatinine-Clr may be considered representative enough for the glomerular filtration rate (GFR). Water, sodium, glucose and L-lactate were absorbed in the renal tubules nearly completely, with a fractional excretion (FE) lower 2%. So they are suitable as endogenous markers for insufficient tubular absorption. Other electrolytes were absorbed incompletely depending on the supply of these substances (calcium-FE and magnesium-FE: 1-50%, potassium-FE: 10-120%, phosphate-FE: 0-5%). An extremely variable part of the filtered urea was reabsorbed in the tubuli (urea-FE 8-85%). For that reason urea is not appropriate for the diagnostic of disturbances of renal functions. A method for clinical determination of renal function by measurement of concentrations of metabolites and electrolytes in blood plasma and spontaneous urine is described and evaluated. The method is based on the supposed constant excretion of the creatinine (0,17 mumol/min/kg) and allows especially the examination of male and sick animals without quantitative sampling of urine. Reference-values for the renal excretion of electrolytes and metabolites of healthy horses are given.