Laboratory risk factors for hospital mortality in acutely admitted patients

Background: Many factors affecting hospital mortality in acutely admitted patients are poorly understood. Although scoring systems exist for critically ill patients, usually in intensive care units (ICUs), there are no specific mortality prediction systems for general acute admissions. Aim: To assess the relationship between simple admission laboratory variables on the risk of in-patient mortality. Design: Retrospective analysis of hospital admissions and laboratory databases. Methods: Where possible, all deceased patients in the 12-month period of study were matched with two surviving controls. The laboratory database was then analysed for admission investigations, including serum sodium, plasma glucose, and white blood cell (WCC) count. Abnormalities of these variables were then compared between cases (those who subsequently died), and controls (those who survived). Results: There were 16 219 admissions, with an overall mortality of 7.6%. We investigated 602 cases and 1073 controls. Hyperglycaemia (glucose >11.0 mmol/l) (OR 2.0, p < 0.0001); severe hyponatraemia (sodium 10 × 109/l) (OR 2.0, p < 0.001) were significantly associated with mortality. The respective associations on logistic regression analysis were: glucose, OR 1.7, p = 0.02; sodium, OR 4.4, p < 0.0001; WCC, OR 1.5, p = 0.006. Low glucose levels, high sodium levels, and low WCC levels were also associated with increased mortality, leading to ‘U-shaped’ mortality associations. The effect of more than one laboratory abnormality being present was cumulative, in a linear fashion. Discussion: Plasma glucose, serum sodium and WCC are measured in most acutely admitted patients, and abnormalities of these variables have associations with in-hospital mortality. This may provide the basis for the development of a mortality risk scoring system.