Many equine illnesses and injuries require rapid determination of blood’s oxygen-carrying capacity. Hemoglobin (Hg) can be measured, and packed cell volume (PCV) can be estimated, providing a good indication of how much oxygen can circulate. However, Hg measurement requires transport of a blood sample to a laboratory. It would be useful if practitioners had the means to accurately measure Hg in the field. Researchers from Cornell University, including Lysa Posner, DVM, recently evaluated such a device called a hemoglobinometer (HemoCue b-hemoglobin photometer, HemoCue Inc, Mission Viejo, Calif.).

“This particular unit is very small and light, and runs on batteries,” says Posner. “This makes it an excellent choice for a mobile unit or field hospital.” The study was designed to determine this hemoglobinometer’s accuracy and precision in measuring Hg and estimating PCV in horses.

Posner and colleagues took blood samples from 43 horses admitted to Cornell University Hospital. The samples were divided for measurements in the hemoglobinometer and the in-house laboratory for comparison. An additional 12 horses had blood samples taken and manipulated by concentration or dilution to provide a range of PCV values from 10-80% (normal range=31-47%). This tested the ability of the hemoglobinometer to measure extreme Hg concentrations.

The results indicated that hemoglobinometer measurements were consistently lower than standard laboratory measurements when Hg concentration ranged from 1.6-16 g/dl (normal range for Hg=11.6-17.9 g/dl). However, the difference was small, typically less than 1 g/dl. In addition, there was a linear relationship in the data between Hg concentration measured by the two methods. This allowed regression equations to be calculated for accurate PCV estimation (multiplying Hg by approximately three). The device was also quite precise, with repeat readings of the same samples differing by less than 0.2 g. However, when Hg concentration was high (16-32 g/dl), and PCV exceeded 45%, hemoglobinometer readings became increasingly variable, underestimating laboratory measurements by as much as 3.2 g/dl. Therefore, it appears that the HemoCue hemoglobinometer is most accurate and precise when used in horses with low to normal Hg levels