Mild Hyponatremia as an Early Marker for Intrathoracic Cancer: A Cohort Study

Intrathoracic cancer can cause hyponatremia, but it is uncertain whether mild hyponatremia in the outpatient setting should be regarded as an early sign of intrathoracic cancer.

To evaluate the risk of undiagnosed intrathoracic cancer in patients with new persistent mild hyponatremia.

We conducted a retrospective cohort study using the electronic health record database of a large healthcare organization. The hyponatremia group included patients with sodium concentration of 130-134 mmol/L twice, after a previous normal value and without previous history of cancer or diseases related to hyponatremia. A control group with normal sodium concentration was matched by sex, age, and year of testing. We measured specific intrathoracic cancer incidence during 3 years of follow-up after sodium concentration test date. A logistic regression was used to adjust for further clinical information including smoking history, symptoms, and medications.

The study comprised 1539 participants with mild hyponatremia and 7624 matched controls. New intrathoracic cancer diagnosis was more common in the hyponatremia group during a 3-year follow-up; 1.49% in the hyponatremia group and 0.39% in the control group, crude odds ratio (OR) 3.84, 95% confidence interval (95%CI) 2.22-6.63. After adjustment, hyponatremia remained a significant risk factor for the diagnosis of intrathoracic cancer; adjusted OR 3.61, 95%CI 2.08-6.28.

New mild persistent hyponatremia might be a significant predictive marker to a yet undiagnosed intrathoracic cancer.