By Ryah Luevano
Updated: Nov 10, 2026
Published: Nov 10, 2026
An “invalid” result can look alarming next to a straightforward positive or negative — but it isn’t a diagnosis on its own, and it isn’t automatically a red flag for tampering. It’s a signal that one or more specimen checks fell outside the expected range, and it’s worth knowing what those checks actually measure before drawing a conclusion.
What a Specimen Validity Flag Actually Checks
Every Southwest Labs toxicology report includes built-in specimen validity testing: creatinine, oxidants, pH, and specific gravity. Each parameter has a normal physiological range, and a result outside that range — on its own — simply means something about the specimen’s composition needs a closer look. Low creatinine alongside low specific gravity can point to dilution from overhydration. An abnormal pH or a detected oxidant can point to an adulterant. None of these, alone, proves intent.
Why This Is Built Into Every Report
Rather than requiring providers to order specimen validity testing separately, Southwest Labs includes these checks as part of the standard toxicology report — so a validity concern surfaces alongside the drug result itself, not after the fact.
What This Means for Your Practice
- Treat an invalid flag as a prompt to look closer, not as proof of an attempt to defeat the test.
- Check which specific parameter triggered the flag (creatinine, oxidant, pH, or specific gravity) before deciding next steps.
- Consider a recollection when validity is in question, rather than treating the original result as final.
- Read the flag against a patient’s testing history, not just in isolation, to decide how to respond.
Southwest Labs is a locally owned, CAP- and CLIA-accredited reference laboratory based in Albuquerque, serving providers across the Southwest with toxicology and infectious disease testing. To review our current toxicology test menu or get started sending samples, contact our team at Info@southwestlab.com or (505) 609-LABS.