Greyhounds have differences in many hematological parameters compared to other breeds [i.e. higher PCV and red blood cell counts], attributed to selective breeding, and to a compensatory mechanism for their high oxygen affinity hemoglobin (Hb). The purpose of this study was to evaluate this oxygen affinity of Hb in retired racing Greyhounds (RRGs) using a blood gas analyzer with cooximeter (Nova CCX), and to establish reference intervals in this breed. Venous blood samples from 57 RRGs (G) and 30 non-Greyhounds (NG) were analyzed, and groups were compared using T-test. The G group had significantly higher pH, partial pressure of oxygen (PO2), oxygen saturation (SO2), oxyhemoglobin (O2Hb), total Hb (tHb), oxygen content (O2Ct), and oxygen capacity (O2Cap) and significantly lower deoxyhemoglobin (HHb) and P50 when compared to NG, supporting the higher oxygen-carrying capacity in this breed. Consistent with previous reports, P50 was lower (high oxygen affinity). Current studies on Hb-based oxygen carriers have revealed that in tissues which need more oxygen, a high-affinity oxygen carrier is beneficial (i.e. strenuous exercise), potentially explaining the benefits of having a high-affinity Hb.
Given the narrow range found in the P50 value, and Greyhounds’ high mean Hct, we postulated that the high viscosity had affected the results by impairing a constant blood flow through the analyzer. Venous samples from 13 RRGs were obtained, and divided in two heparinized tubes, diluting one to 20% with PBS. Both undiluted and diluted samples were analyzed simultaneously, and P50 was also calculated manually (formula in the user’s manual). No significant differences were found among undiluted and diluted samples, but when calculated manually, mean P50 was significantly lower than the one generated by the instrument in both undiluted and diluted samples. In conclusion, the high viscosity did not affect the results obtained in the previous study.
In order to evaluate the P50 variation during storage, venous blood from 19 RRGs was analyzed and then stored at 4°C for 3 weeks. At this time, the analysis was repeated and the two time points were compared. The mean P50 value decreased, but unexpectedly, almost half of the values remained the same after 3 weeks.
The Hemox-Analyzer is an instrument that accurately records and plots the oxyhemoglobin dissociation curve (ODC) during deoxygenation, providing information about the delivery of oxygen to the tissues. We evaluated venous samples from two adult dogs (one RRG and one mixed breed); both dogs had blood gas and cooximetry analysis performed too. Although both dogs had the same P50 using the Nova CCX, the Greyhound had lower P50 than the mixed breed dog using the Hemox-Analyzer.
Overall, we conclude that Greyhounds have high affinity Hb, as reflected by a low P50, compared to NG. However, this is not accurately assessed by the Nova CCX analyzer, probably because it is not designed for animals (uses human ODC algorithms). Based on limitations imposed by the machine’s calculation of P50, higher SO2 in Greyhounds (>80%) could also make the analyzer assign a default value, explaining such a narrow range in P50 values.