Serum and urinary biochemistry and enzyme changes in ponies with acute renal failure

Serum and urinary biochemical changes were recorded in 5 ponies in which acute tubular nephrosis had been induced over 5 days with mercuric chloride and potassium dichromate. Serum osmolality, the serum concentrations of urea nitrogen, creatinine, sodium, potassium and chloride, and blood pH and blood gases were measured daily for 14 days or until humane euthanasia was performed. Levels of the same substances were quantitated daily in urine. In addition, routine urinalyses and determination of urinary gamma glutamyl transferase (GGT) activity were performed on each sample. Changes in the values of the urinary variables preceded alterations in the serum value of the same substance by at least one day. The first notable abnormality detected was in urinary GGT activities. These changes occurred up to 6 days before the detection of azotemia. It was concluded that acute equine renal injury could be diagnosed earliest with biochemical testing of urine. Measurement of urinary GGT levels represents a means by which proximal tubular disease in equidae could be diagnosed in its developmental stages.