Hospital-acquired serum phosphate derangements and their associated in-hospital mortality

Background We aimed to report the incidence of hospital-acquired hypophosphataemia and hyperphosphataemia along with their associated in-hospital mortality. Methods We included 15 869 adult patients hospitalised at a tertiary medical referral centre from January 2009 to December 2013, who had normal serum phosphate levels at admission and at least two serum phosphate measurements during their hospitalisation. The normal range of serum phosphate was defined as 2.5-4.2 mg/dL. In-hospital serum phosphate levels were categorised based on the occurrence of hospital-acquired hypophosphataemia and hyperphosphataemia. We analysed the association of hospital-acquired hypophosphataemia and hyperphosphataemia with in-hospital mortality using multivariable logistic regression. Results Fifty-three per cent (n=8464) of the patients developed new serum phosphate derangements during their hospitalisation. The incidence of hospital-acquired hypophosphataemia and hyperphosphataemia was 35% and 27%, respectively. Hospital-acquired hypophosphataemia and hyperphosphataemia were associated with odds ratio (OR) of 1.56 and 2.60 for in-hospital mortality, respectively (p value<0.001 for both). Compared with patients with persistently normal in-hospital phosphate levels, patients with hospital-acquired hypophosphataemia only (OR 1.64), hospital-acquired hyperphosphataemia only (OR 2.74) and both hospital-acquired hypophosphataemia and hyperphosphataemia (ie, phosphate fluctuations; OR 4.00) were significantly associated with increased in-hospital mortality (all p values <0.001). Conclusion Hospital-acquired serum phosphate derangements affect approximately half of the hospitalised patients and are associated with increased in-hospital mortality rate.