July 12, 2016 | From the Lab Bench

Validities Tests, Part 2: General Oxidant, pH and Temperature

jill headshot webBy Jill Warrington, M.D.
Burlington Labs Chief Medical Officer




Every urine sample screened at Burlington Labs gets tested for four “validity” parameters: pH, general oxidant, specific gravity and creatinine. These values help us flag samples that may have been tampered with.

In our last newsletter, we explained the basic science behind two of those parameters: creatinine and specific gravity. (If you missed that discussion, that article is still available on our website here.) This month, we’ll take a closer look at pH and general oxidant, and explain why temperature is no longer an entirely foolproof way to validate a UA sample. 

There are three main strategies used by patients trying to “beat a drug test.” The most common strategy is urine dilution, which was covered in last month’s discussion of creatinine and specific gravity. Another tactic is for the patient to add a substance to the urine after collection that will break down any drugs that are present. Household products like bleach, ammonia, baking soda, detergent, lemon juice or vinegar, and commercially-available “flush kits” containing oxidizing chemicals, can either degrade the drugs present in the sample, or interfere with the enzyme immunoassay analysis of a specimen, or both. One might think that this can’t happen with observed collections, but substances can be well hidden and surreptitiously flicked into the sample, for example, having the substance under one’s fingernail.

If the collector doesn’t spot this activity during an observed collection, we’re able to flag those adulterated samples in the lab by analyzing for pH and general oxidant. When lemon juice or vinegar is added to a specimen, the urine becomes highly acidic, which is reflected in a pH lower than 3. When something like bleach or ammonia is added, the urine becomes highly basic (11 or greater). When an oxidant is added to a specimen, the General Oxidant value shows positive.

So if any of your patients’ drug test reports show abnormal results on the pH or general oxidant values, chances are that he or she added something to their specimen at the time of collection to attempt to mask the presence of drugs or drug metabolites in their urine.

A third strategy used by patients trying to beat a drug test is urine substitution. A patient will bring someone else’s drug-free urine into the collection room, either in a bag under their clothes, in a catheter, or in a balloon-like device hidden inside the vaginal or anal areas. The internet provides many ingenious and creative devices designed specifically for this purpose. Testing for temperature at the time of collection used to be able to flag any UA samples that did not come from the patient’s own bladder, since the temperature of those samples (which were typically brought into the collection room in a bag or container) would typically be lower than normal human body temperature.

Unfortunately, many of the catheter or balloon vessels sold online now have built-in temperature controls, designed to ensure that the urine comes out at normal human body temperature. So temperature’s value as a validity measure is no longer foolproof.

Questions about validities are some of our most common “FAQs,” and our scientists are always happy to speak with providers about test results.