Carstens was arrested for allegedly driving under the influence of alcohol nearly three years ago.
The Cape Argus reported that his lawyer Milton de la Harpe questioned the quality of work done by State forensic analyst Pakami Pati in the Cape Town Magistrate's Court on Thursday.
De La Harpe said the results compiled by Pati could not be accurate, because the test solutions were used long after the specified time frame in which they should have been used.
"I put to you that out of the six standards used, only two passed the specifications stipulated and four were done after eight weeks," he said.
"How can you say that is good quality-work that fulfils the requirements of the National Metrology Institute of SA?"
Puti maintained that the tests she did were accurate.
She reportedly said in her evidence-in-chief that the alcohol laboratory complied with national and international standards.
The case was postponed until May 8 for further cross-examination. Bail of R500 was extended.
- SAPA