False-positives in urine drug screening caused by medications

Testing urine for the presence of drugs has a variety of uses including assessing poisoning or overdose, pre-employment testing, substance abuse treatment monitoring, or other medicolegal purposes.  There are a number of common medications that can cause false-positive screening of these tests which can lead to a variety of ramifications.

Initial tests are usually performed with an immunoassay.  These can generally be done quickly (an hour or two) and inexpensively and vary in their sensitivity.  They may miss particular substances (for opioids in particular – synthetic or semisynthetic opioids such as hydrocodone, oxycodone, fentanyl, or methadone may not test positive on the initial immunoassay) so if you’re suspicious/concerned about a certain agent, let the lab know so the correct test is performed.  Following the immunoassay, positive results can be confirmed with a more specific technique such as gas chromatography or mass spectrometry but these tests are more costly and time consuming so results may not be available for hours to days. 

Here is a table of medications that can cause false-positives on the urine immunoassay and some comments about the caveats of each category.

Update on steroid recommendations for COPD exacerbations

Let’s start with a patient case.  An elderly patient is admitted through the emergency department with markedly worsening dyspnea and purulent sputum production over the last three days.  When reviewing his history, you find that he has GOLD grade 4 (very severe) COPD and experiences roughly one exacerbation per year that requires hospitalization.  His home medications for COPD include tiotropium (Spiriva) 18 mcg/inhalation once daily, albuterol MDI (Proventil HFA, ProAir HFA, or Ventolin HFA) 90 mcg/inhalation 2 inhalations every 4-6 hours as needed for dyspnea, and fluticasone/salmeterol (Advair Diskus) 250/50 mcg inhaled twice daily.  You are now deciding what steroid regimen should be initiated to manage this exacerbation.