London  - The current doping test in sport for the steroid testosterone is not suitable because of ethnic variations, a Swiss study published on Thursday revealed.

The study was commissioned by the ruling football FIFA and carried out among 171 players around the world.

The results were examined at the Lausanne, Switzerland, lab approved by the World Anti-Doping Agency (WADA), and published in the "British Journal of Sports and Medicine."

Testosterone is a natural hormone but has also been used as a performance-enhancing doping substance by athletes, including American cyclist Floyd Landis and baseballer Alex Rodriguez.

The study revealed "significant differences" in the so-called testosterone-epitestosterone ratio with which the use of synthetic testosterone is to be detected.

The official WADA benchmark of 4:1 was surpassed by Hispanics (5.8:1), Caucasians (5.7:1) and Africans (5.6:1) while Asians registered 3.8:1 in the tests after steroids were added to their urine samples.

"These results demonstrate that a unique and nonspecific threshold to evidence testosterone misuse is not fit for purpose," said the study.

The study suggested that a biological passport for athletes should replace the current test method, with suspicious levels then leading to targeted doping tests.

Wilfried Schaenzer, head of the doping lab in Cologne, Germany, did not make much of the findings, saying "we know for a long time that different people produce different levels of testosterone."

Schaenzer said that the so-called isotope test can still determine whether synthetic testosterone was added.

However, he also said "it will be the likely strategy to introduce the biological passport."