sentences:  Laboratory findings will show a decreased packed cell volume (PCV) that is usually less than 20%, an increased bilirubin, especially unconjugated bilirubin, and occult blood in the urine.A definitive diagnosis can only be made if alloantibodies are discovered in the mare's serum or colostrum and are shown to be against the foal's red blood cells.Such tests include crossmatching the mare's serum to washed red blood cells of the foal, which is added to exogenous complement, and is positive if hemolysis occurs.