Sperm Chromatin Evaluation Methods in Infertility

One of the main spermatogenesis events is the replacement of histones with small proteins called protamines, which leads to chromatin's condensation in the sperm nucleus and protects it against possible damage. Today, tests such as aniline blue (AB), toluidine blue (TB), and chromomycin A3 (CMA3) staining are used based on different characteristics to evaluate sperm chromatin compaction. For the assessment of DNA fragmentation in sperm, several tests such as 8-hydroxy-2-deoxyguanosine (8-OHdG), TUNEL, Comet, sperm chromatin structure assay (SCSA), sperm chromatic dispersion (SCD), and acridine orange have been introduced that directly and indirectly assay DNA damage. The articles in PubMed and Google Scholar, as well as related books, from 2007 to 2022, were collected and reviewed based on keywords 8-OHdG, TUNEL, Comet, SCD, and acridine orange. So far, many studies have been conducted at the treatment level and on sperm chromatin tests, but the number of cases published so far is limited. Various sperm samples have been used in different studies, with different threshold limits in the tests. The sixth edition of the World Health Organization (WHO) book notes that each laboratory has its threshold limit. Therefore, in this review study, common methods of evaluating chromatin packaging and DNA damage are introduced, and the advantages and disadvantages of each test are discussed based on the latest achievements related to infertility.