RESUMEN
BACKGROUND: Knowledge of biological variation (BV) is important for determining analytical goals and for establishing the magnitude of change between two consecutive measurements which indicate change in a patients' health status. The aim of this work is to determine the BV for total choriogonadotropin (ß chain) (ß-hCG) and α-fetoprotein (AFP) in patients diagnosed with testicular cancer but with no evidence of recurrence of disease. METHODS: We estimated BV from a mean of five consecutive measurements in 28 patients diagnosed with testicular cancer, 3 months after tumor resection or 4 months after complete treatment with chemotherapy. The mean sampling interval was 3 months. RESULTS: The mean concentrations of α-fetoprotein and choriogonadotropin (ß chain) were 3.9 µg/L and 0.79 IU/L, respectively. Between-run analytical variation was 7.1% at 4.1 µg/L for α-fetoprotein, and 19% at 0.65 IU/L for choriogonadotropin (ß chain). BV obtained for α-fetoprotein and choriogonadotropin (ß chain) was 12.4% and 16.7%, respectively, and the reference change value (RCV) for one-tail showed 38.2% and 60.7% for α-fetoprotein and choriogonadotropin (ß chain), respectively. CONCLUSIONS: The estimation of BV allows us to calculate analytical goals and RCVs, necessary tools for the correct interpretation of serial measurements in the follow-up of patients.