Objective: It has been predicted that 60-70 % of critical decisions are based on laboratory results. Sodium is one of the most frequently tested analytes in the clinical laboratory. Hyponatremia is common inconvenience of sodium metabolism in hospital patients, with a prevalence of 2% to 3%. We describe here a case of factitious hyponatremia caused by the presence of liquefied gel layer in the serum tube.

Material and Methods: A 56 year woman was admitted to the Emergency for head ache, nausea, sweating and hypertension. Sodium test is performed on a Beckman Coulter AU5800 using serum collected into 13 × 100 mm, 5 mL BD Vacutainer according to manufacturer’s instruction.

Results: Extremely low value of serum sodium (106 mmol/L) was measured and test repeated on same sample (74 mmol/L). When we check the tube we detected liquefied gel layer in tube. Liquefied gel has occured because temperature is rised in the intensively using centrifuge. We had another serum tube for hormone test and sodium test was measured again from this tube, result was 137 mmol/L which is compatible her clinical status. Last result (137 mmol/L) reported to the clinician.

Conclusion: The cause of extremly low serum sodium value is incomplete serum aspiration volume by the sample probe of the instrument. Laboratory staff should be aware that falsely low sodium results due to interference of the liquefied gel. Alternatively whole blood sodium can be measured using a direct ion-selective electrode. Finally it might be useful cooled centrifuge use in sodium measurements.