Increases in 2,3-diphosphoglycerate concentration in blood from horses with poor performance due to respiratory disorders

Abstract

Poor performance in racehorses is often due to subclinical respiratory disorders that are likely associated to hypoxia even in resting conditions. During hypoxia, the concentration of 2,3-diphosphoglycerate (2,3DPG) in blood increases, facilitating the release of oxygen to tissues. Thus, 2,3DPG is a candidate biomarker for detection of respiratory origin following a poor performance episode. The objective of this study was to determine the 2,3DPG concentrations in blood from resting horses with poor performance due to respiratory disorders and assess its diagnostic utility. To this aim, 2,3DPG was measured in blood from 11 standardbred horses with inflammatory airway disease (IAD), 5 with exercise-induced pulmonary haemorrhages (EIPH), and 7 control horses. IAD and EIPH were diagnosed by cytology and bacteriology on bronchoalveolar lavage fluids. The diagnostic sensitivity, specificity, and the likelihood ratio of 2,3DPG increases were also evaluated. 2,3DPG (μmol/g Hb) was higher in horses with EIPH (33.77±5.03) and IAD (27.69±7.37) compared to controls (18.23±4.70). This increase was associated with augmented haemoglobin and haematocrit. The optimal cut-off to discriminate horses with respiratory disorders from controls was 21.78 μmol DPG/g Hb. These results demonstrate that 2,3DPG is increased in blood from horses with IAD or EIPH, likely due to the presence of hypoxia and the measurement of 2,3DPG may have clinical utility in the diagnosis of poor performance in horses: elevated 2,3DPG levels may be used to suspect respiratory origin for poor performance in horses before resorting to more expensive and invasive techniques.