Pre-analytical validity of arterial blood gas samples: A prospective experimental study on changes derived from time delay and mechanical stress

Abstract

Background: Time delays and mechanical stress of samples obtained for Point of Care (POC) blood gas analyses are common; however, their influence on the results of these analyses has not been systematically investigated. Our study aimed to investigate the effect of prolonged time before analysis and mechanical manipulation on pre-analytical stability of biomarkers and thus the validity of the results of blood gas analyses. Methods: We collected blood samples from 240 patients in a university surgical intensive care unit. These samples were immediately analyzed following the clinical standard operating procedures. Subsequently, the sample containers were allowed to rest for 60 min, then subjected to standardized mechanical forces, and analyzed again. We analyzed 13 typical blood gas biomarkers, comprising respiratory gases, electrolytes, and protein biomarkers. Bland–Altman plots were prepared to analyze the differences between the test runs. The differences between the test groups were compared against the official limits of accuracy specified in the German requirements for quality assurance of medical laboratory tests. Results: For hemoglobin, creatinine, glucose, and electrolytes (including calcium, sodium, chlorine, and bicarbonate), the agreement between the immediate and post-interference-treatment analyses was within the ranges specified in the official requirements. For pH and potassium, the deviations were outside the quality assurance ranges but within a clinically acceptable measurement accuracy. Only oxygen partial pressure and lactate levels were altered to such an extent that they can no longer be used for clinical purposes. Conclusion: Even after a 60 minutes time delay and excessive mechanical stress, selected blood gas analysis biomarkers such as Hemoglobin, Glucose, Sodium, Calcium, Chloride, and Bicarbonate could be considered valid. Potassium and pCO2 were altered but suitable for approximation purposes. Findings for pO2 and Lactate were generally incorrect. In the future, in selected settings, these findings can aid in reducing unnecessary blood sampling in vulnerable patients.