What makes a drug test invalid?

An invalid drug test can occur if a urine sample contains an unknown substance or contaminant. It can also occur if the sample contains a substance at abnormal concentrations or with abnormal characteristics. There are a number of possible underlying reasons why these issues may occur with a sample. Possibilities include:

1. Dilution of the specimen

An analysis of urine specimen validity for drug abuse testing in workplace and court testing found that dilution was the predominant method of tampering in workplace urine specimens. A urine specimen would be considered a diluted specimen and a testing result invalid if creatinine levels and gravity values within the sample are lower than expected for human urine.

2. Adulteration of the specimen

An adulterated specimen would cause a urine test to be invalid. It could alter the pH of the sample, sending it outside the normal expected range. Human urine normally has pH of around 7 but it can be lower or higher as a result of certain medications, health issues or even a person's diet. The urine specimen will be seen as invalid if the pH is outside the range of 3-11 (or perhaps slightly narrower). Specimens that are stored at high temperatures for long periods of time can produce high pH values. However, these environmental conditions are still unlikely to produce a result higher than 9.5, which is still considered valid.

A pH level outside of the 3-11 range suggests evidence of tampering. A person may attempt to lower the pH of their urine and produce an invalid result by drinking something like vinegar to lower their urine pH level. Other household chemicals added to the urine sample can indicate adulteration and produce an invalid result. These include substances such as ammonia, bleach and glutaraldehyde.

3. Substitution of the urine sample

Some people may attempt to substitute their sample for urine that is not their own. This could be attempted by using powdered urine that has been mixed with water, synthetic urine, or by using another person's urine. This method of cheating may or may not be picked up on unless the testing facility has very sophisticated testing procedures. However, it will likely be picked up if the person providing the substituted specimen fails to keep it at a normal urine temperature.

A person being tested might also substitute their urine for sports drinks or soft drinks, which would be picked up as an invalid test.