A new report from the Garda Professional Standards Unit says some Gardai are taking DNA samples without proper training.
The details are contained in the GPSU's annual report for 2018.
The GPSU carried out research among Gardai in conjunction with the National Forensic Co-Ordination Office.
It found only 55% of Gardai surveyed had received some form of training in the taking, submission, retention and destruction of DNA samples while 81 percent of those interviewees are actually engaged in taking DNA.
Some Gardai said taking they had used a 'How To' video on their internal web page to help them carry out DNA sampling duties.
Following the review, the GPSU says there is a lack of oversight and governance and the issue needs urgent attention.