Original article / research
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Effect of Lipemia on Measured and Calculated Osmolality in Native Lipemic Samples and Intravenous Lipid Emulsion-Added Pools |
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| Correspondence
Address : Dr. Medine Alpdemir, Department of Clinical Biochemistry, Balikesir State Hospital, Ministry of Health, Balikesir, Turkey. E-mail: bitigic@hotmail.com |
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Introduction: Lipemia are common interferences in clinical laboratories. They particularly cause interference because of the electrolyte exclusion effect on indirect Ion Selective Electrodes (ISE) methodologies. This may produce falsely low Na and K values, thereby leading to pseudohyponatremia and pesudohypokalemia. However, the effect of lipemia on measured Osmolality (mOSM) and calculated Osmolality (cOSM) remains unknown. Aim: To investigate the effect of lipemia on mOSM and cOSM values in naturally lipemic samples of high concentration and pools simulating lipemia according to different calculation formulae. Materials and Methods: In the first phase, serum samples of 55 patients with Triglyceride (TG) concentrations of >7.91 mmol/L were collected from routine clinical care. The concentrations of OSM, TG, Glucose (Glc), urea, Na, and K were measured before and after high-speed centrifugation. OSM was measured with a freezing-point depression osmometer. The 18 OSM formulae that is applied was utilised for OSM calculations. In the second phase, lipemia interference was assessed in Intravenous Lipid Emulsion (IVLE) added sera. Starting serum pools that had 0.95 mmol/L TG concentrations were prepared from fresh-clear serum. Then, by mixing of one unit of IVLE {Intralipid 20%, Clin Oleic (Baxter, Old Toongabbie, NSW)} with 19 units of starting pool, the first pool was made. This first pool with IVLE had an intralipid concentration of 10 g/L. The concentrations of OSM, TG, Glc, urea, Na, and K were measured before and after IVLE addition. Statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS®) for Windows, version 16.0 software (IBM, Chicago, USA). Results: In the first phase of study, there were no significant differences in the mOSM concentrations between non-lipemia and lipemia samples. However, there was a significant difference between non-lipemia samples and lipemia samples for cOSM in all formulae (p<0.001). Further, there was a significant difference between mOSM and cOSM in the lipemia samples. There was no significant difference between the cOSM of the lipemic samples and mOSM of the non-lipemic samples according to the F11 and F18 (p=0.651, p=0.841). In the second study phase, although there was increased cOSM level dependent on diminished TG concentrations in IVLE-supplemented pools, mOSM levels were reduced. Conclusion: This study demonstrated that lipemia does affect the accuracy of cOSM. Lipemia does not affect mOSM when performed with a freezing-point depression method. OSM should not be calculated because of interference of lipemia. |
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