Which opioids should never test negative on an immunoassay opiate screen, and which opioids may result in a negative test, depending on dose?
The two naturally occurring opiates, morphine and codeine, should always test positive on an immunoassay opiate screen. Synthetic and semisynthetic opioids including hydrocodone, oxycodone, and their metabolites plus oxymorphone and hydromorphone will often test negative, depending on the dose. However, lower doses may result in a positive test, and higher doses may result in a negative test, depending on factors such as urine concentration or hydration status.