The short answer is to have him ask to be retested IMMEDIATELY to confirm the results. Unfortunately, they are not obligated to retest him. If his request to be retested is denied, then he should seek to get tested IMMEDIATELY by an independant lab. If he was represented by the Public Defender, have him contact their office RIGHT AWAY to discuss the possibility of having the PD get any remaining sample tested or to have him tested again. If the PD is willing or able to accomodate, then the County will pick up the tab (pay for the testing). But if he was represented by a private attorney, then he will likely have to pay for the testing himself. Either way, he needs to find out if the lab kept any excess sample (known as a split). If they have, he (or his lawyer) needs to ask them to release the split to a lab of your choosing to have it tested (again, at your expense). If the split results come back negative, then you can challenge the positive test in Court at a probation violation hearing. You will need to have the testing facility send someone to court to testify as to the results, again, at your expense. For the future, to avoid possible false positives, if the testing facility does not agree to save a "split", have the Judge order that a split be prepared from every sample taken and then have each sample tested at the facility of your choosing (again, at your expense).