I think this could be the first truly objective test for male infertility

Dr Peter Sutovsky

A joint team of US and Japanese researchers report in the journal Human Reproduction that the presence of a particular natural molecule or protein may indicate such a problem.

A test for the presence of the protein could be more reliable than other ways of analysing the quality of sperm, it reports.

The protein is called ubiquitin, and is associated with the process by which the body breaks down and recycles other proteins from cells which are damaged or dysfunctional.

The presence of ubiquitin in a sperm cell suggests that all is not well within.

Dr Peter Sutovsky, of Oregon Health Sciences University said: "Ubiquitin appears to be a marker of semen abnormalities, recognising a wide range of sperm defects and also contaminants in semen.

"I think this could be the first truly objective test for male infertility, based on an exact, fully automated measurement of a single protein in sperm rather than a subjective analysis of sperm by light microscopy.

"Its major advantage is its sensitivity. We were able even to diagnose a male factor in cases where conventional semen analysis could not explain infertility.

"In around one fifth of all couples, current methods cannot identify a cause."

The technique was tested on 17 patients from couples unable to conceive.

The test confirmed five cases in which other methods had diagnosed male subfertility - and identified five other cases in which male factors might be the cause.

And in another three cases, they found problems with male subfertility in addition to the previously-diagnosed fertility problems of their partner.

The team believes that the technique could help sort defective sperm from normal examples to increase the chances of success in intracytoplasmic sperm injection (ICSI).

Dr Gerald Schatten, also from Oregon, said: "Since we now know a specific protein is associated with defective sperm, and we have antibodies against it, there is a chance we could develop a technique for depleting most of the truly defective sperm from semen samples for IVF or ICSI."