Using red blood cell creatine concentration to evaluate the equine erythropoietic response

Red blood cell creatine concentration was examined to determine its association with the equine erythropoietic response. Studies were conducted on 9 healthy horses, 4 healthy ponies, 24 anemia horses, and 2 horses in which anemia was experimentally induced. A modified Jaffe reaction was used to measure RBC creatine concentration. The mean RBC creatine concentration of the 9 healthy horses was 5.72 +/- 0.42 mg/dl, and that of the 4 healthy ponies was 2.59 +/- 0.31 mg/dl. Density-separation of erythrocytes from the healthy horses revealed significantly higher (P less than 0.001) creatine content (7.72 +/- 0.57 mg/dl) in the young RBC populations than in the old RBC populations (4.03 +/- 0.27 mg/dl). The RBC creatine content was assayed in 19 hot-blooded horses which were anemic due to a variety of causes. Of these anemic horses, 12 with PCV between 25% and 30% had a mean RBC creatine concentration of 6.12 +/- 0.46 mg/dl. The 7 other anemic horses with PCV less than 25% had a mean RBC creatine value of 6.07 +/- 0.12 mg/dl. Bone marrow films were examined from 5 anemic horses and in the 2 horses in which anemia was experimentally induced. The RBC creatine concentration correlated positively (P less than 0.001) with the reticulocyte count in the bone marrow and negatively with the myeloid-erythroid ratio (P less than 0.001).