Renal tubular acidosis (RTA) is a sporadic disorder in horses. The RTA may be preceded by drug therapy for another condition or renal injury, or there may be no predisposing cause. RTA may be transient or recurring. Genetic predisposition is unproved but possible in recurring cases, which has been noted in Friesian horses. The exact type of renal tubular acidosis, eg, type 1 or type 2, is hard to determine in most equine RTA cases because herbivores normally have alkaline urine, and anorexia by itself will cause a decrease in urine pH.
Signs of renal tubular acidosis include acute onset of depression, anorexia, muscle trembling, and tachycardia and/or arrhythmia. There are many differential diagnoses for these clinical signs, so serum chemistry testing and urinalysis are necessary to confirm the diagnosis. There is a severe metabolic acidosis, marked hyperchloremia, and often hypokalemia with equine RTA. The urine pH is usually neutral to alkaline. Blood parathyroid hormone and vitamin D have been increased in some horses with RTA, but the significance and cause of this has not been determined.
Administration of sodium bicarbonate IV and PO is generally successful in correcting the metabolic acidosis from renal tubular acidosis. Potassium supplementation may be critical if the serum potassium concentration is <2.5 mEq/L or if the horse is trembling or has cardiac arrhythmias. Treatment throughout a few days may result in complete resolution in some horses, but others (likely genetic) may require continued supplementation with sodium bicarbonate administered PO.
Renal tubular acidosis may be preceded by drug treatment or renal injury, but some cases have no predisposing cause.
Clinical signs are nonspecific, so laboratory tests are needed for diagnosis.
Sodium bicarbonate is generally successful in correcting the metabolic acidosis, but if hypokalemia is present then potassium supplementation may be needed as well.
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