Relationships between the erythrocyte sedimentation rate, plasma proteins and viscosity, and leucocyte counts in thoroughbred racehorses.

The influence of plasma proteins on erythrocyte aggregation was studied in a population of young thoroughbred racehorses, using the 60 minute erythrocyte sedimentation rate (ESR) with and without haematocrit standardisation. The ESR was correlated inversely with the haematocrit, but directly with fibrinogen, plasma viscosity and serum total globulins. When ESR values were standardised to a common haematocrit the correlation coefficients for the same plasma protein factors were increased. Albumin levels showed a strong direct relationship with haematocrit which accounted for the inverse correlation found between albumin and ESR. The haematocrit standardised ESR showed no significant correlation with albumin levels. Total leucocyte and absolute neutrophil counts were not correlated with either ESR or haematocrit standardised ESR. The high correlation (r = 0.75) found between fibrinogen levels and haematocrit standardised ESR suggests that differences in this acute phase protein influence the degree of red cell aggregation and rouleaux formation in the horse.