Comparison of serum parathyroid hormone and ionized calcium and magnesium concentrations and fractional urinary clearance of calcium and phosphorus in healthy horses and horses with enterocolitis

Objective-To evaluate calcium balance and parathyroid gland function in hea lthy horses and horses with enterocolitis and compare results of an immunoc hemiluminometric assay (ICMA) with those of an immunoradiometric assay (IRM A) for determination of serum intact parathyroid hormone (PTH) concentratio ns in horses. Animals-64 horses with enterocolitis and 62 healthy horses. Procedures-Blood and urine samples were collected for determination of seru m total calcium, ionized calcium (Ca2+) and magnesium (Mg2+), phosphorus, B UN, total protein, creatinine, albumin, and PTH concentrations, venous bloo d gases, and fractional urinary clearance of calcium (FCa) and phosphorus ( FP). Serum concentrations of PTH were measured in 40 horses by use of both the IRMA and ICMA. Results-Most (48/64; 75%) horses with enterocolitis had decreased serum tot al calcium, Ca2+, and Mg2+ concentrations and increased phosphorus concentr ations, compared with healthy horses. Serum PTH concentration was increased in most (36/51; 70.6%) horses with hypocalcemia. In addition, FCa was sign ificantly decreased and FP significantly increased in horses with enterocol itis, compared with healthy horses. Results of ICMA were in agreement with results of IRMA. Conclusions and Clinical Relevance-Enterocolitis in horses is often associa ted with hypocalcemia; 79.7% of affected horses had ionized hypocalcemia. B ecause FCa was low, it is unlikely that renal calcium loss was the cause of hypocalcemia. Serum PTH concentrations varied in horses with enterocolitis and concomitant hypocalcemia. However, we believe low PTH concentration in some hypocalcemic horses may be the result of impaired parathyroid gland f unction.