TUNEL assay and SCSA determine different aspects of sperm DNA damage

For the determination of sperm DNA damage, different assays are used. However, no further distinction is made and the literature generally speaks about DNA damage. Thus, this study aimed at comparing the sperm chromatin structure assay (SCSA) and the TUNEL assay. In 79 patients, sperm DNA damage was determined flow cytometrically using the SCSA and the TUNEL assay. Moreover, normal sperm morphology was evaluated according to strict criteria. A statistical comparison of the two methods was performed using standard correlations, Bland and Altman plots, Passing-Bablok regressions and concordance correlation. Results show a significant difference between P- and G-pattern morphology only for the mean channel fluorescence of the SCSA. Spearman's rank correlations between the different parameters of both assays, SCSA and TUNEL, revealed significant associations between the parameters of the assays. However, when applying Bland and Altman plots, Passing-Bablok regression and concordance correlation results showed that these methods are not comparable. These different techniques determine different aspects of sperm DNA damage, i.e. 'real' DNA damage for the TUNEL assay and 'potential' DNA damage in terms of susceptibility to DNA denaturation for the SCSA. Thus, one should clearly distinguish between the different assays, not only practically and methodologically but also linguistically.