SST and PST can cause decreases in which two drugs?

• A. TCA and anti-arrhythmics
• B. Analgesics and antibiotics
• C. Theophylline and caffeine
• D. ACE inhibitors and diuretics

Answer: (A)

The main idea is that separator gels in SST and PST tubes can bind or trap certain drugs, leading to lower measured levels in the sample. Hydrophobic, lipophilic drugs are especially prone to adhering to the gel or the tube’s silicone-coated surfaces during processing, so tricyclic antidepressants and antiarrhythmic medications tend to show decreased recovery in these tubes. Because these drugs don’t stay fully in the serum or plasma, the assay may report a lower concentration than is actually present. This is why, for monitoring levels of TCAs and many antiarrhythmics, clinicians and labs often prefer non-gel tubes or rapid processing to avoid the adsorption effect. The other drug groups listed are less consistently affected by gel separators, so the strongest and most reliable pattern is seen with TCAs and antiarrhythmics.