Atypical Pseudohyponatremia He ´ le ` ne Girot, 1 Marion De ´ hais, 1 Franc ¸ ois Fraissinet, 1 Julien Wils, 1 and Vale ´ ry Brunel 1* CASE DESCRIPTION A 3-year-old girl with Alagille syndrome and Hashimoto thyroiditis presented with unexpected hyponatremia. She was previously known for hyponatremia associated with edema when hypothyroidism was diagnosed. At clinical examina- tion, no edema was observed. Biological values are shown (Table 1). QUESTIONS 1. What are common causes of pseudohyponatremia? 2. What methods can be used to distinguish pseudohyponatremia from genuine hyponatremia? 3. What is the cause of pseudohyponatremia in this case? The answers are below. ANSWERS Hypertriglyceridemia and hyperparaproteinemia are the most common causes of pseudohyponatremia when so- dium is measured using indirect potentiometry (1, 2 ). The expected decrease in sodium due to lipids can be calculated (3) and in this case would be approximately 5 (versus the observed approximately 15) mmol/L. Chronic cholestasis secondary to Alagille syndrome likely led to increased lipoprotein X (4), not ac- counted for in the calculation. In cases of suspected pseudohyponatremia, direct ion-selective electrode methods or osmolal gap calculations can be helpful for laboratory management (5). Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 require- ments: (a) significant contributions to the conception and design, acquisi- tion of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article. Authors’ Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest. References 1. Kim GH. Pseudohyponatremia: does it matter in current clinical practice? Electrolyte Blood Press 2006;4:77– 82. 2. Melnick S, Nazir S, Gish D, Aryal MR. Hypertriglyceridemic pancreatitis associated with 1 Department of Medical Biochemistry, Rouen University Hospital, Rouen, France. * Address correspondence to this author at: Department of Medical Biochemistry, Rouen Uni- versity Hospital, 1 Rue de Germont, Institut de Biologie Clinique, Service de Biochimie Ge ´ne ´ rale, 76000 Rouen, France. Fax +33-023-288-1456; e-mail valery.brunel@chu-rouen.fr. Received May 17, 2017; accepted June 23, 2017. DOI: 10.1373/clinchem.2017.276501 © 2017 American Association for Clinical Chemistry Table 1. Blood sample results from lithium heparin tube. Result Reference interval Sodium, mmol/L (ISE) 123 135–145 Total protein, g/dL 5.7 6.5–8.0 Triglycerides, mg/dL a 250 44–133 Cholesterol, mg/dL a 1807 120–230 Osmolality, mosm/kg 294 290–300 Calculated osmolality, mosm/kg b 262 290–300 Sodium, mmol/L (DSE) 138 135–145 a Conversion factors for SI units: triglycerides mg/dL × 0.011 = mmol/L; cholesterol mg/L × 0.026 = mmol/L. b Calculated osmolality = [(sodium + potassium) × 2 + urea + glucose]. All results expressed in mmol/L. ISE, indirect ion-selective electrodes; DSE, direct ion-selective electrodes. What Is Your Guess? 414 Clinical Chemistry 64:2 (2018) Downloaded from https://academic.oup.com/clinchem/article/64/2/414/5608856 by guest on 30 August 2022