Hyponatremia in lung cancer: Incidence and prognostic value in a Danish population-based cohort study

Hyponatremia is a common electrolyte disorder in lung cancer patients, especially in patients with small-cell lung cancer (SCLC). It has been proposed as a prognostic indicator of higher mortality; however, data have been conflicting. Here, we determine the incidence and prognostic impact of pretreatment hyponatremia in a large Danish registry-based cohort of lung cancer patients.

Data on lung cancer patients diagnosed from January 2009 to June 2018 in The Central Denmark Region were extracted from the Danish Lung Cancer Registry and combined with data on the pretreatment sodium level extracted from the clinical laboratory information system. Hyponatremia was defined as a sodium level <135 mmol/l. Cox proportional hazard models assessed the prognostic value of hyponatremia on overall survival (OS) in patients with non-small cell lung cancer (NSCLC) and patients with SCLC.

A total of 6995 patients with NSCLC and 1171 with SCLC were included. The hyponatremia incidence was 16 % among patients with NSCLC and 26 % among patients with SCLC. Hyponatremia was associated with an inferior OS in patients with NSCLC (<135 mmol/l: median 0.46 years (95 % CI: 0.41-0.51) vs. ≥ 135 mmol/l: median 1.05 years (95 % CI: 1.00-1.11)), p < 0.001; adjusted hazard ratio (HR) = 1.45 (95 % CI: 1.34-1.56)) as well as in patients with SCLC in (<135 mmol/l: median 0.67 year (95 % CI: 0.58-0.73) vs. ≥ 135 mmol/l: median 0.73 years (95 % CI: 0.67-0.78); p = 0.0035; adjusted HR = 1.21 (95 % CI: 1.04-1.41)).

The incidence of pretreatment hyponatremia is high in patients with SCLC as well as with NSCLC. Hyponatremia seems to be an independent predictor of inferior survival in lung cancer patients, especially in patients with NSCLC.