Screening and Diagnosis: Instruments, Cutoffs, and Lab Windows
Screening and Diagnosis tests the instruments, their cutoffs, and the reasoning that turns a positive screen into a diagnosis. Expect questions naming a tool for a specific population, asking what a score means, or asking which test detects recent use.
Screens you must recognize
- AUDIT (10 items, 0-40): 8 or more indicates hazardous drinking; AUDIT-C uses the first three items.
- CAGE (4 yes/no): Cut down, Annoyed, Guilty, Eye-opener; 2 or more is a positive screen - a screen, not a diagnosis.
- MAST and DAST-10 cover alcohol and other drugs respectively.
- T-ACE and TWEAK are pregnancy-specific; any alcohol use in pregnancy warrants brief intervention.
- CIWA-Ar grades alcohol withdrawal and guides benzodiazepine dosing; COWS grades opioid withdrawal and guides buprenorphine induction.
- SBIRT: universal screening, brief intervention, referral to treatment.
Laboratory windows
- Alcohol: breath or blood for recent hours; ethyl glucuronide up to about 3 days in urine, longer in hair.
- Cocaine metabolite (benzoylecgonine): 2-4 days.
- Opioids: 1-3 days; cannabis can persist for weeks in heavy users because of fat storage.
- Urine immunoassays give false positives (poppy seeds, pseudoephedrine, some antibiotics) and need confirmatory GC-MS.
From screen to diagnosis
DSM-5 requires a pattern causing impairment or distress within the past 12 months; severity follows the criterion count (2-3 mild, 4-5 moderate, 6 or more severe). Diagnose remission when criteria are no longer met - early remission 3-12 months, sustained beyond 12. Rule out other explanations such as hypoglycemia, head injury, delirium, or prescribed medication effects before labeling intoxication.
Worked example
A 52-year-old is admitted for pancreatitis. He answers yes to CAGE items 1 and 4 ("cut down," "eye-opener") and reports drinking to avoid tremor. Reasoning: CAGE is positive at 2, but diagnosis needs the full DSM-5 interview, which here yields withdrawal and use despite physical harm. The eye-opener plus tremor signals dependence with withdrawal risk; plan CIWA-Ar monitoring and benzodiazepines if symptoms appear.
Traps
- Treating a positive CAGE as a diagnosis.
- Using a urine screen to prove impairment - it shows exposure, not intoxication.
- Missing the long cannabis detection window and misreading a positive result as very recent use.