If you have found your way to this page, there is a reasonable chance you have already read a great deal about sperm DNA fragmentation, quite possibly late at night, and come away more unsettled than when you started. Some of what you read will have told you this test explains everything a standard semen analysis missed. Some of it will have told you the test is worthless and NICE has said so. Both of those things are being said in public, by people who are not fools, and neither is quite the whole picture.

Before anything else, since it is probably why you are here: an elevated result is not a verdict, and it is not a statement that you cannot father a child. Here is what I want to do on this page: set out what the test measures, why the laboratories disagree with one another, what the evidence does and does not support, and why two serious guideline bodies have landed in different places. Then you can decide, with your clinician, whether the result would actually change anything for you — which is the only question that really matters.

A declaration first. I have no commercial interest in sperm DNA fragmentation testing. I do not sell it, I do not have an arrangement with a laboratory that performs it, and I earn nothing whether you have it or you do not. I should also say plainly that I am a urological surgeon: I perform varicocele repair, and I am involved in surgical sperm retrieval. Both are mentioned on this page. On a question this contested you are entitled to know whether the person explaining it stands to gain from your answer — and to notice that the argument I go on to make is an argument against acting on the number.

What the test actually measures

A standard semen analysis counts sperm, watches how they swim, and looks at their shape. It says nothing about the genetic material inside the head of the sperm. Sperm DNA fragmentation testing attempts to fill that gap: it estimates what proportion of sperm in a sample carry breaks — single-stranded or double-stranded — in their DNA.

The rationale is intuitive. A sperm that swims perfectly well may still be carrying damaged genetic cargo. Damage can arise during sperm production, during maturation and transport, or from oxidative stress — a chemical imbalance in which reactive molecules outpace the body's ability to neutralise them, and which is influenced by things like smoking, obesity, infection, heat and age. The result is usually expressed as a DNA Fragmentation Index, a percentage of affected sperm.

That is where the intuitive part stops.