Extreme biochemical patient results in a routine hospital laboratory

Biochemical tests are crucial in acute patient care, and the validity of the results is important. We aimed to evaluate extreme results reported in a routine hospital laboratory and to review patient characteristics. This is a retrospective cohort study of extreme laboratory results reported at the Department of Clinical Biochemistry, Aalborg University Hospital, Denmark (2022-2024). For six common analytes (sodium, potassium, creatinine, calcium, phosphate, and magnesium), the most extreme low (<i>n</i> = 25) and high (<i>n</i> = 25) results were identified. Electronic health records of 284 unique patients were reviewed to determine pathophysiological causes, pre-analytical errors, clinical course, and 7-day survival. Among 5,794,014 biochemical test results, 300 extreme results (0.005%) were identified, with 261 (87.0%) being compatible with a pathophysiological cause, and 39 (13.0%) being caused by a pre-analytical error. For high results, renal failure was the predominant cause (54.1%), particularly affecting creatinine, phosphate, and potassium. For low results, low creatinine was caused by muscle atrophy, while for other analytes, the most common causes were malnutrition, alcoholism, sepsis, diarrhea/emesis, and diuretics. The 7-day survival was lower for patients with extremely high results (77.4%) compared to low (94.5%). In conclusion, in a routine hospital laboratory, extreme biochemical test results were often pathophysiological, with pre-analytical errors accounting for around 10% of the reported results. Survival was generally high and patients with extremely low results had higher survival compared to those with extremely high results. Results inform the laboratory's decision-making on the handling and release of extreme biochemical results.