Determination of the biological variation of S100β and lactate dehydrogenase in disease-free patients with malignant melanoma

Background: Biological variation is important for determining analytical goals and for establishing the magnitude of change between two consecutive measurements. The aim of this study was to determine the biological variation for S100 beta and lactate dehydrogenase in patients diagnosed with malignant melanoma but without evidence of disease recurrence. Methods: The biological variation of S100 beta and lactate dehydrogenase was estimated from a mean of four consecutive measurements in 32 patients diagnosed with malignant melanoma but without evidence of disease recurrence, 3 months after tumor resection or 4 months after finishing adjuvant treatment. The mean sampling interval was 3 months. Results: Mean concentrations of S100 beta and lactate dehydrogenase were 0.0557 mu g/L and 6.3 mu kat/L, respectively. Between-run analytical variation was 3.5% at 0.181 mu g/L for S100 beta and 3.5% at 2.83 mu kat/L for lactate dehydrogenase. Biological variations obtained for S100 beta and lactate dehydrogenase were 14.2% and 8.2%, respectively. The analytical goals (defined as 50% of biological variation) were 7.1% for S100 beta and 4.1% for lactate dehydrogenase. Conclusions: The estimation of biological variation allows us to calculate analytical goals and reference change values. These are necessary tools for the correct interpretation of serial measurements in patient follow-up.