SUN-661 Appropriate Assessment In Pseudohyponatremia To Avoid Improper Fluid Resuscitation

Abstract P.M. Francis-Emmanuel: None. M.S. Boyne: None. L.A. Chin-Harty: None. A.P. Williams: None. C.R. Swaby: None. S.C. Browne: None. J.M. Plummer: None. Background: Pseudohyponatremia (as measured by the commonly used indirect ion-selective electrode method) may result from biliary tree obstruction and other causes of high cholesterol. It may also occur in conditions resulting in high serum protein levels as seen in multiple myeloma. Direct ion-selective electrode methods of measuring serum sodium offer accurate readings and may avoid injudicious attempts at sodium correction. Clinical case: A 64-year-old man with no past medical illnesses presented to hospital with periumbilical pain, pale stool, and dark urine. He denied polyuria or polydipsia and had no alcohol nor diuretic use. Examination revealed a euvolemic patient with deep jaundice, and a soft, non-tender abdomen. He had ichthyosis and xerosis but no necrolytic migratory erythema and his neurologic examination was normal. Blood investigations revealed total bilirubin 590 (4 - 18) umol/L, direct bilirubin 542 (2 - 6) umol/L, total cholesterol 17.6 (1.2 - 5.2) mmol/L, LDL-C 17.0 (0.5 - 3.4) umol/L, glucose 9.3 (4.0 - 7.0) mmol/L and sodium 128 (135 - 145) mmol/L. Computerised tomography of the abdomen revealed an obstructing but resectable pancreatic head tumour with marked dilatation of intra- and extrahepatic bile ducts. In the absence of the required laboratory equipment within the chemical pathology laboratory to perform serum sodium measurement using direct ion selective electrode (ISE), serum osmolality was measured and compared with calculated osmolality using values obtained in the same sample: {2 (Na) + glucose + urea}. Calculated total serum osmolality = 258.1 mOsm/kgMeasured serum osmolality = 283.0 mOsm/kgOsmolar gap = 24.9 mOsm/kg This wide osmolar gap (> 10 mOsm/kg) supported the diagnosis of pseudohyponatremia. Using a blood gas analyzer to assess serum sodium was an alternative and could have also been used for a more accurate assessment of serum sodium. The patient had Whipple’s procedure with a prompt rise in serum sodium to 137 mmol/L, measured by indirect-ISE, immediately post-operatively. This. rose from a nadir of 124 mmol/L pre-operatively. Total bilirubin 179 (4 - 18) umol/L, direct bilirubin 159 (2 - 6) umol/L, total cholesterol 6.6 (1.2 - 5.2) mmol/L and LDL-C 5.0 (0.5 - 3.4) mmol/L also improved. Hyponatremia is the most encountered electrolyte abnormality in hospitalized patients. Care needs to be taken when assessing total body sodium. Addressing the underlying cause of pseudohyponatremia results in correction of serum sodium levels and will avoid unnecessary attempts at fluid resuscitation. Sunday, June 2, 2024