AFP, CEA, CA125 and CA19-9 are commonly used serum tumour markers (TMs) in clinical practice, although their quantification by immunoassay may be influenced by pre-analytical sample handling. Though the effect of repetitive freeze-thaw cycles is generally recognized, it is not clear in detail. The present study measured (CLIA) these TMs in serum samples freshly separated and after each of five freeze-thaw cycles, in which the samples were frozen at -40 degrees C for 10 months at cycle 4 and 2 h at other cycles. Statistical analysis with the General Linear Model for Repeated Measures revealed significant decreases in the measurements of the four TMs, with the least decrease of 6.8 % for CA125 and the most decrease of 18.2 % for CA19-9 after the last cycle, and an overwhelming single cycle decrease of mean 7.7 % at cycle 4 for AFP, CEA and CA125, of 7.5 % and 9.3 % at cycles 4 and 5 for CA19-9. So it seems that measurements of AFP, CEA and CA125 are more readily affected by long-term frozen storage compared with frequent freezing-thawing, while CA19-9 is relatively unstable under both conditions.
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