The effects of time delay and temperature on capillary blood gas measurements

Monitoring of blood gas measurements is an important part of the assessment of patients with chronic lung disease. Increasingly, this is being done in the patients' homes by specialist nurses. This makes it important to know the effect of time delay and storage temperature on the reliability of capillary blood gas analysis results. In this study, the effect of a delay of 1 and 2 h and of storage at both room temperature and in ice, on blood stored in glass capillary tubes was investigated. Samples, initially taken from the earlobes, were transferred to glass capillary tubes and used to provide duplicate initial samples for immediate analysis, and then single samples at 1 and 2 h stored at room temperature or in ice. The duplicate baseline measurements showed good reproducibility. There was a small, but statistically significant, increase in PCO2 when samples were stored in capillaries at room temperature, or in ice, both at 1 and 2 h. Small changes in PO2 were not statistically significant, either in ice or at room temperature. None of the changes was considered to be sufficient to be of clinical significance, thus supporting the use of capillary blood sampling even when there might be a delay of 1-2 h and transport is at room temperature, as might be the case when taking domiciliary samples.