Sample evaporation from pierceable cups: still an important source of analytical error.

BACKGROUND: We illustrate the impact of sample evaporation on analytical results in laboratory practice and highlight preventive measures. METHODS: Plasma (n=10) was analysed for glucose, Na(+), HCO(3)(-) and calcium on six different sample configurations at 5 time points within 2h. RESULTS: With time glucose, Na(+) and calcium values increased and HCO(3)(-) values decreased in a clinically significant way. CONCLUSIONS: Analytical error due to evaporation may be significant, but can be reduced with optimal sample handling. A pierceable cover does not prevent loss of HCO(3)(-).