Effect of Time Delay at Ambient Temperature on Serum Electrolytes and Comparison of Electrolyte Concentrations in Plasma and Serum

The present study was aimed at investigating the effect of time delay at ambient temperature on laboratory investigation of serum electrolytes and to compare the electrolytes concentrations in plasma and serum. The study was conducted by recruiting 32 healthy individuals of 22-35 years. Whole blood samples (6 mL) were collected from each individual and plasma and serum were separated. Serum was divided into four aliquots. One aliquot was analysed immediately after the separation (baseline value) and other three aliquots were kept for 1, 3 and 5 hours at ambient temperature (28-30 °C). The plasma and serum electrolytes; Na+, K+, Cl- and iCa2+ concentrations were measured by ST-200 Plus Electrolyte Analyzer. There were no statistically significant differences in serum Na⁺ concentrations between serum analysed immediately after separation (142.60±2.31 mmol/L) and serum kept for 1 hour at ambient temperature (142.63±2.27 mmol/L) (p>0.05). Similarly, no statistically significant differences were observed in serum Cl⁻ concentrations between serum analysed immediately after separation (101.27±1.46 mmol/L) and serum stored at ambient temperature for 1 hour (101.43±1.48 mmol/L) and 3 hours (101.55±1.39 mmol/L) (p>0.05). Comparison of baseline plasma and serum electrolyte concentrations demonstrated no statistically significant difference in Na⁺ concentrations between plasma (142.75±2.23 mmol/L) and serum analysed immediately after separation (142.60±2.31 mmol/L) (p>0.05). However, a statistically significant difference was observed between plasma and serum K⁺ concentrations, with plasma showing 4.09±0.31 mmol/L and serum analysed immediately after separation showing 4.21±0.31 mmol/L (p<0.05). Likewise, a statistically significant difference was observed between plasma and serum iCa²⁺ concentrations, where plasma showed 1.25±0.03 mmol/L and serum analysed immediately after separation showed 1.27±0.03 mmol/L (p<0.05). No statistically significant difference was observed between plasma (101.54±1.33 mmol/L) and serum analysed immediately after separation (101.27±1.46 mmol/L) in relation to Cl⁻ concentrations (p>0.05). Immediately separated plasma following blood collection can be suggested as the sample of choice for the determination of Na⁺, K⁺, Cl⁻, and iCa²⁺ when multiple electrolyte parameters are analysed from a single sample.