Application of electrolyte analysis of pleural effusion to diagnosis of drowning

We measured concentrations of sodium (Na), chloride (Cl), calcium (Ca), and magnesium (Mg) in pleural effusion from forensic autopsy cases to examine whether they were useful for a diagnosis of drowning. We analyzed a total of 51 cases (15 seawater drowning, 10 freshwater drowning, and 26 non-drowning), and determined the following reference values. If the concentration of Na or Cl is under 65 mEq/l, a diagnosis of freshwater drowning can be made. If the concentration of Na is higher than 175 mEq/l, or that of Cl is higher than 155 mEq/l, or that of Ca is higher than 16 mg/dl, or that of Mg is higher than 15 mg/dl, a diagnosis of seawater drowning can be made. We recommend that pleural effusion from the left and the right thoracic cavities should be collected and analyzed separately because large differences may be observed between each side in the case of drowning. If one side corresponds to the reference value for seawater or freshwater drowning and the other side does not, a diagnosis of drowning can still be made according to the obtained value.