|Sample Requirement||Turnaround Time|
Paired serum & urine
Same working day
In horses with normal renal tubular function, urinary excretion rate of creatinine is almost constant. It can therefore be used as an arithmetic constant to produce a measure of the fractional excretion of electrolytes and minerals in equine urine.
Concentrations of electrolytes or minerals are measured in serum and urine samples collected at the same time or at least within 1 hour of one another. Diuretics must not be used to stimulate urination or spurious results will be obtained. The percentage excretion of each electrolyte can then be calculated. Fractional excretion rates for sodium, potassium, chloride, magnesium, calcium and phosphate are most commonly measured. The result provides an assessment of the horse’s homeostatic regulatory status for that electrolyte or mineral, e.g. sodium and chloride may be selectively excreted at an increased rate because of excessive dietary salt intake. Phosphate may be excreted at an increased rate to try to maintain a normal serum calcium:phosphate ratio in the face of inadequate calcium intake.
Fractional urinary electrolyte and mineral clearance ratios are often increased in horses with nephropathy, in particular with renal tubular malfunction. Impaired renal tubular function results in high urine excretion rates for all the electrolytes and minerals, from failure of retention. In such cases, creatinine is no longer a valid arithmetic constant.
In secondary nutritional hyperparathyroidism, which occurs in horses on a high phosphate diet, phosphate excretion rate is high, indicating the need for oral calcium supplementation and phosphate reduction, to restore balance.
Urinary phosphate clearance ratios are useful measures of calcium:phosphate balance in weanlings and yearlings, important for bone growth and development. Calcium:phosphate imbalance can predispose to physitis.