The Daily Voice reported that Carstens’ lawyer Milton de la Harpe questioned the validity of the tests while cross-examining blood analyst Pakama Pati in the Cape Town Magistrate’s Court on Wednesday.
The lawyer said another doctor had questioned the method and the results of the blood tests.
However, Pati, who tested Carstens’ blood, said the health department’s alcohol laboratory complied with national and international standards.
Carstens, the former Springbok Nude Girls frontman, was pulled over in the Cape Town CBD in December 2010 when a traffic officer apparently saw his black Mercedes-Benz swerve.
He told the newspaper all he wanted was for the trial to be completed after lengthy delays over the last three years.
The trial was postponed until April 25 for the defence to go over the information received from the blood expert.