Male Fertility Basics: Sperm DNA Fragmentation Tests: 101
DNA fragmentation in male sperm is a rising and increasingly missed cause of male factor infertility. The accuracy of sperm DNA fragmentation tests is critical to identifying the underlying cause of infertility in couples.
There are four main procedures used to test for DNA fragmentation in male sperm, each of which measures different aspects of sperm health. In this blog, we will discuss the various forms of procedures that test for DNA fragmentation in male sperm, including Sperm Chromatin Structure Analysis (SCSA), TUNEL assay, SCD (sperm chromatin dispersion test), and the COMET test.
Sperm Chromatin Structure Analysis (SCSA) The SCSA test is performed using fresh ejaculate and examines around 5000 spermatozoa. The sperm is stained with a special technique, allowing sperm with intact double-strand DNA to be visible as green, while sperm with broken (fragmented, single-strand) DNA appear as red. The relation between green and red spermatozoa is calculated, and a fragmentation index (DFI) is determined. The DFI is classified as follows: a) Excellent to good (less than or equal to 15% DFI) b) Good to fair (greater than 15% to less than 25% DFI) c) Fair to poor (greater than or equal to 25% to less than 50% DFI) d) Very poor (greater than or equal to 50% DFI) There is research that suggests that this type of DNA fragmentation test can be used as a predictor for IUI (Intrauterine Insemination) outcomes.
TUNEL assay (terminal deoxynucleotidyl transferase dUTP nick end labelling) The TUNEL assay measures broken DNA by detecting the presence of certain hydroxygroups (3’-OH-groups) at the free ends of the DNA fragments. The enzyme TdT is used to attach nucleotides to the hydroxygroups, which can be made visible using fluorescence in a microscope.
SCD (sperm chromatin dispersion test) or ‘halo’ test The SCD or ‘halo’ test measures sperm with intact DNA. Sperm with intact DNA have ‘halos’, which represent dispersed chromatin without strand breaks. Sperm with fragmented DNA do not have halos, so haloless sperm cells represent those with DNA damage. A normal result would show less than 20% of cells with fragmented DNA.
COMET test The COMET test is the only procedure that measures double-strand breaks separately. The test is based on the ability of negatively charged loops/fragments of DNA to be pulled through an agarose gel in response to an electric field, appearing like a ‘comet’. The undamaged DNA nucleoid part is referred to as the ‘head’, and the trailing damaged DNA streak is referred to as the ‘tail’. The percentage of DNA in the tail is directly proportional to the percentage of DNA damage that has occurred in a particular cell. There are two types of COMET test, the alkaline COMET test and the neutral COMET test.
There is disagreement between experts about which DNA fragmentation test is the best and what the standard results of the tests should be. Some tests don't even have a clear definition of a "normal" result. Different DNA fragmentation tests can give different results and have different levels of accuracy in predicting male infertility. A study in 2019 compared the ability of five different tests to predict infertility and found that the alkaline comet test was the best, followed by the TUNEL assay, SCD test, and SCSA. Experts in the field of andrology recommend carefully considering the results of the tests and always noting which test was used.
Understanding the different procedures and the results they provide can help couples identify the underlying cause of infertility and find the right treatment path.
In the majority of cases, there is much that can be done to improve DNA fragmentation and sperm health naturally. Please reach out to set up and appointment with Dr. Shamus to discuss how acupuncture, Eastern Medicine and simple dietary and lifestyle shifts can maximize your fertility profile.
