Stability of carboxyhemoglobin in stored and mailed blood samples.

BACKGROUND Elevated blood carboxyhemoglobin (COHb) levels are used to confirm a clinical diagnosis of exposure to carbon monoxide (CO) and, in some instances, assess severity of poisoning. However, many hospital laboratories cannot measure COHb because they do not have CO-oximeters. In such instances, blood samples are often sent to outside laboratories or with a transported patient for measurement at the receiving hospital. This study was conducted to assess the stability of COHb in stored and mailed blood samples anticoagulated with heparin. METHODS Adult human blood was drawn into standard sample tubes anticoagulated with sodium heparin. Carbon monoxide gas was infused to raise the COHb level to 25% to 35%. Samples were then refrigerated or stored at room temperature, and serial COHb determinations were performed for 28 days. Additional samples were measured after being mailed locally or across the United States and back. RESULTS No significant changes in COHb levels were seen in samples stored either in refrigeration or at room temperature over a period of 28 days or in samples shipped without refrigeration locally or across the United States. CONCLUSIONS Carboxyhemoglobin levels in whole blood samples anticoagulated with heparin are stable with or without refrigeration for up to 4 weeks. If COHb measurement capability is not available, such samples may be shipped or transported with patients with confidence that the COHb level will be stable when measured at a later time.