Incidence of hyponatremia in a cohort of patients with colorectal cancer.

Abstract

545 Background: Hyponatremia (HN), a common electrolyte disturbance in hospitalized patients, is a prognostic factor in some cancers. The incidence of HN in patients diagnosed with colorectal cancer (CRC) is unknown and is investigated here. Methods: This retrospective cohort analysis combined electronic medical record and tumor registry data from an integrated delivery network. Patients included were adults diagnosed with incident invasive CRC between 2005 and 2011 with ≥1 administration of radiation or chemotherapy within 6 months of diagnosis who met continuous clinical activity criteria. Exclusions included unknown index cancer stage or ≥1 post-index hypovolemic HN episode. Patients were followed until study end, death, clinical trial entry, new primary cancer onset, or end of continuous clinical activity. HN incidence (serum sodium ≤135 mEq/L) was measured per 1,000 person years (PY) of observation (95% confidence intervals [CI]) and classified as mild (131–135), moderate (125–130) or severe (<125) based on the lowest observed value. Results: In all, 132 CRC patients were included (52% male; mean [SD] age 64±13.1 years, 99% Caucasian). Mean (SD) follow-up was 3±2.6 years. Thirty-six percent of patients had metastatic disease at diagnosis and 80% received chemotherapy, 39% radiation therapy and 83% surgical resection. Patients with HN post-CRC diagnosis had significantly greater incidence of metastatic disease during follow-up (p=0.033) and exposure to anti-metabolites (p=0.023) or platinum based agents (p=0.017). Episodes of HN (n=262) occurred in 81 patients (61%) at a rate of 598 per 1,000 PY (95% CI, 523–680). Mean (SD) episodes per patient were 1.8±2.6. Overall, 84% of episodes were mild, 14% moderate and 2% severe; 52% were classified as syndrome of inappropriate antidiuretic hormone secretion. Mean (SD) time to first hyponatremia episode was 139±296 days, with a median duration of 12 days; 84% of patients had a first episode within the first 6 months. Conclusions: The incidence of HN after diagnosis with CRC was about 61% and episodes occurred primarily within 6 months of diagnosis. Based on these results, along with emergent evidence from other studies, clinicians should anticipate HN in newly-diagnosed CRC patients.