Association between serum phosphate level and mortality of patients with aneurysmal subarachnoid hemorrhage

Disorders of serum phosphate, including hyperphosphatemia and hypophosphatemia, have been confirmed to be related to the poor prognosis of specific critically ill patients. No study analyzes the relationship between continuous serum phosphate level and mortality from aneurysmal subarachnoid hemorrhage (aSAH). This study was performed to explore this relationship. aSAH patients were divided into four groups based on serum phosphate quartiles. Significant factors discovered in the univariate Cox regression were included in the multivariate Cox regression to explore the independent relationship between serum phosphate and mortality of aSAH. Kaplan-Meier survival analysis was performed to compare the difference in survival between the four groups. The 60-day mortality of overall aSAH patients was 20.7%. The mortality of the group with the 1st quartile (29.4%) and the 4th quartile (24.7%) had higher mortality than others (p = 0.028). Univariate Cox regression showed the 2nd quartile (p = 0.020) and 3rd quartile (p = 0.017) were associated with lower mortality risk than the 1st quartile. Compared with the 1st quartile, the 4th quartile was not associated with lower mortality risk (p = 0.458). After adjusting confounding effects, multivariate Cox regression showed only the 4th quartile was significantly associated with higher mortality risk (p = 0.009) than the 1st quartile. The unadjusted relationship between serum phosphate and mortality of aSAH is U-shaped. While high serum phosphate even within the normal range is independently related to the mortality of aSAH. Low serum phosphate may be just a marker for the severity of aSAH. Evaluating the initial serum phosphate is useful for risk stratification of aSAH.