Objectives: To standardize the TUNEL assay by establishing inter- and intraobserver variability, interassay variability, cutoff values, sensitivity and specificity of the assay, and studying the distribution of the DNA damage in a population of infertile men referred to a clinical andrology laboratory.
Methods: Seminal ejaculates from 25 healthy male volunteers (controls) and 194 infertile men (with male factor infertility) referred to an andrology laboratory were examined for DNA damage by TUNEL assay using flow cytometric analysis.
Results: Both the inter- and intraobserver variability and interassay variability was small (<10%). DNA damage in the controls was 11.9 ± 6.8% vs. 29.5 ± 18.7% in patients (P <.001). The cut-off value of 19.25% maximized the observed sensitivity (64.9%) and specificity (100%) of the assay. The distribution of DNA damage in the patients was as follows: 14.9% (29 of 194) with DNA damage between 0% and 10%; 22.7% (44 of 194) between 10% and 20%; 8.8% (17 of 194) between 20% and 30%; and 17.5% (34 of 194) between 30% and 40%. Finally, 27.3% (53 of 194) had TUNEL values >40%.
Conclusions: We report a detailed standardization of the TUNEL assay for clinical use, as well as reference ranges for DNA damage in normal healthy donors and infertile men. A cut-off of 19.25% with observed 100% specificity established in our program can differentiate infertile men with DNA damage from healthy men. This test can be offered to infertile patients who are idiopathic, have severe oxidative stress-related abnormal semen quality, and contribute to the infertility problem of the couple who are considering assisted reproductive techniques.
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