Influence of spurious hemolysis on blood gas analysis.

BACKGROUND

Although the prevalence of hemolyzed samples referred for blood gas analysis is as high as 4%, no studies have assessed the bias introduced by spurious erythrocyte breakdown, nor it is known which parameters are mostly influenced and to what extent. This study was hence planned to assess the influence of spurious hemolysis on venous blood gas analysis.

METHODS

Venous blood was collected from nine healthy volunteers in sodium heparin tubes and divided in two aliquots of 3 mL. The former aliquot was mechanically hemolyzed by aspiration with 0.5 mL insulin syringe equipped with 30 gauge needle. One milliliter of all aliquots was tested for hemoglobin, pH, oxygen partial pressure (pO₂), partial pressure of carbon dioxide (pCO₂), bicarbonate (HCO³⁻), oxygen tension at 50% hemoglobin saturation (p50), oxygen saturation (sO₂), actual base excess (ABE), carboxyhemoglobin (COHb), methemoglobin (metHb), ionized calcium (Ca²⁺) and potassium, on ABL800 flex. The remaining 2 mL of blood were centrifuged, plasma separated and tested for hemolysis index.

RESULTS

The concentration of cell-free hemoglobin increased from <0.5 g/L to 8.9±1.5 g/L in hemolyzed aliquots. In hemolyzed blood, significant decreases were found for pH (-0.2%), pO₂ (-4.9%), sO₂ (-4.9%), COHb (-11%) and Ca²⁺ (-7.0%), whereas significant increases were observed for pCO₂ (+4.1%), HCO³⁻ (+1.4%) and potassium (+152%). Clinically meaningful bias was found for pO₂, pCO₂, Ca²⁺ and potassium.

CONCLUSIONS

Spurious hemolysis is likely to introduce meaningful biases in blood gas analysis, hence manufacturers of blood gas analyzers should develop instrumentation capable of identifying interfering substances in whole blood. The presence of spurious hemolysis should also be suspected whenever test results do not reflect the clinics.