Evaluation of the Diagnostic Accuracy of the Most Commonly used Equations for Calculation of Osmolarity in Paediatric Population BC15-BC17
Vardhaman Mahavir Medical College and Safdarjung Hospital, New Delhi, Delhi, India.
Introduction: Serum osmolality is an essential laboratory parameter to understand various clinical disorders including dehydration status, electrolyte disturbances and exogenous intoxication. The measured serum osmolarity by using basic plasma components such as glucose, urea and electrolytes is an indirect indicator of serum osmolality. While several equations are available for calculation of serum osmolarity, their diagnostic predictive accuracy for estimation of serum osmolality remains debatable.
Aim: To determine the most accurate equation for calculation of serum osmolarity in Paediatric population.
Materials and Methods: The present retrospective study was conducted on 50 apparently healthy children (aged =12 years) at Chacha Nehru Bal Chikitsalya, Paediatric Government Hospital, Delhi. Serum urea, sodium, potassium, glucose (Glu) and osmolality values were obtained from the January 2016- December 2016 laboratory records. Osmolarity was calculated using most commonly used nine prediction-equations. Students’ paired t test was used to assess the statistical differences between measured and calculated osmolarity by different equations. Pearson correlation coefficient test was used to analyse the correlation between the calculated osmolarity and measured osmolality. The Bland Altman method and Regression analysis were used to determine the agreement and differential bias between calculated osmolarity and measured osmolality.
Results: The mean of measured osmolality was 293.86±10.89 mOsm/kg. The equation for calculating serum osmolarity by Smithline Gardner: 2(Na)+Glu+Urea, (all components were measured in mmol/L) with statistical insignificant difference between the measured osmolality (p-value>0.05), osmolal gap close to zero and maximum r squared value along with the lowest standard error, was best able to predict measured serum osmolality.
Conclusion: Assessment of panel of serum osmolarity equations showed that Smithline Gardner equation had best diagnostic accuracy in Paediatric population and therefore we recommend that the equation should be adopted at different clinical and analytical laboratories platforms.