Hospitalized patients with too low or too high serum phosphate levels upon admission have increased risks of dying during their stay, according to new study findings published in Hospital Practice. Patients with cardiovascular disease (CVD) or chronic kidney disease (CKD) appear especially vulnerable.
Of 42,336 patients hospitalized at Mayo Clinic in Rochester, Minnesota, from 2009 to 2013, those admitted with serum phosphate less than 3.1 or more than 4.2 mg/dL had higher risks for in-hospital mortality than those with values falling within 3.1 to 4.2 mg/dL (reference), Wisit Cheungpasitporn, MD, and colleagues reported. After adjustment, serum phosphate levels less than 2.5 and more than 4.2 mg/dL were associated with in-hospital mortality in a U-shaped relationship. The risk of death increased 1.6 times when serum phosphate was less than 2.5 mg/dL, and 3.9 times when it was 4.9 mg/dL or higher compared with the reference range. CKD and CVD patients who were hyperphosphatemic upon admission had the worst survival. The risk of death increased 4.1 and 5.1 times, respectively, among CKD and CVD patients with phosphate values of 4.9 mg/dL or higher.
“An increase in the in-hospital mortality among patients with elevated serum phosphate levels in our study could be explained by the higher prevalence of renal comorbidities in those with hyperphosphatemia, resulting in higher mortality,” Dr Cheungpasitporn’s team stated. “However, this association remained significant after multivariate analyses adjusted for eGFR [estimated glomerular filtration rate] and comorbidities.” According to the investigators, previous studies have shown a relationship between hyperphosphatemia and cardiovascular events even in patients with normal kidney function.
Hypophosphatemia was associated with in-hospital mortality in CVD but not CKD patients, but the number of cases may have been too small to detect a significant difference.
Cheungpasitporn W, Thongprayoon C, Mao MA, Kittanamongkolchai W, Sakhuja A, and Erickson SB. Admission serum phosphate levels predict hospital mortality. Hosp Pract. DOI: 10.1080/21548331.2018.1483172