Feline Heinz bodies interfering in standard bicarbonate analysis by the ABL90 FLEX

Venous blood gases were analyzed with ABL90 FLEX in two cats with Heinz bodies in approximately 60% of the erythrocytes. The instrument demonstrated an inability to correctly report standard bicarbonate (stHCO₃ ^- ), hematocrits, and hemoglobin concentrations by indicating an OXI spectrum mismatch alarm (ie, the spectrum of measured hemoglobin forms differed from the spectrum of calculated forms). Actual bicarbonate (aHCO₃ ^- ) did not indicate any errors. The ABL90 FLEX uses spectrophotometry to measure hemoglobin, and the presence of Heinz bodies interfered with the measurement in these cases. Because hemoglobin is included in the formula for calculating stHCO₃ ^- , the instrument gave an alarm for stHCO₃ ^- . At follow-up, Heinz bodies were present in only 2%-3% of the erythrocytes, and the ABL90 FLEX did not indicate any alarm messages. To the authors' knowledge, these are the first cases reported that have interference in stHCO₃ ^- measurements due to Heinz body formation using the ABL90 FLEX, a common blood gas instrument used in both veterinary and human critical care. The methodology used for evaluating acid-base status should be taken into consideration, and caution is needed when interpreting acid-base results in cats with Heinz bodies.