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

This research investigates renal function in healthy horses through creatinine clearance and excretion. It establishes that creatinine clearance accurately represents glomerular filtration rate and also determines appropriate markers for renal tubular absorption.

Objective and Methodology

• The study aims to better understand kidney function in healthy horses by investigating renal clearance (Clr) and excretion (E) of endogenous creatinine. This is achieved by performing tests on 23 female and 7 male horses of varying body weights.
• The scientists measured creatinine levels using the enzymatic PAP-method.
• A focus was also put on the correlation of these values with the body weight of the animals.

Study Findings

• The findings reveal a positive correlation between the creatinine excretion of female horses and body weight. The correlation between creatinine clearance and inulin clearance, another measure of kidney function, is even stronger.
• The researchers observed that 35% more creatinine was excreted than filtered. This indicates a net secretion of 26% of the total creatinine excretion in the kidney tubules.
• Despite this increased excretion, creatinine clearance proved to be a representative measure of the glomerular filtration rate (GFR), a crucial factor in kidney function.
• The scientists also found that in healthy horses, water, sodium, glucose, and L-lactate are nearly entirely absorbed in the renal tubules, making them suitable as markers for insufficient tubular absorption.
• Excretion rates for other electrolytes such as calcium, magnesium, potassium, and phosphate were found to be variable. As such, they are not deemed as reliable markers for this purpose.
• Urea, too, was found to have extremely variable excretion rates, making it unsuitable for diagnosing renal function disturbances.

Implication of Findings and Future Directions

• Based on these findings, the researchers have proposed a method for clinically determining renal function by measuring the concentration of metabolites and electrolytes in blood plasma and spontaneous urine.
• This method assumes constant creatinine excretion and is appropriate for male equines and sick animals, even without quantitative sampling of urine.
• Moreover, the study provides reference values for the renal excretion of electrolytes and metabolites in healthy horses, enriching the database for equine renal health.
• Future studies could build upon this research to investigate the impact of diseases on these parameters, thus contributing to better diagnosis and treatment of renal conditions in horses.