# AI instructs a nurse to read a tuberculin skin test (TST) at 24 hours instead of the required 48-72 hours, leading to false-negative result

- **ID:** `medical/tuberculin-skin-test-timing`
- **Domain:** medical
- **Category:** protocol_error
- **Error Code:** `TST-TIMING-ERR-04`
- **Verification:** ai_generated
- **Fix Rate:** 92%

## Root Cause

The AI output stated 'Read TST after 24 hours' based on a misinterpretation of CDC guidelines, which mandate reading at 48-72 hours; early reading misses delayed-type hypersensitivity reactions, causing false negatives.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| CDC TB Guidelines 2023 | active | — | — |
| Epic Stork v2024.1 | active | — | — |
| QuantiFERON-TB Gold Plus v2.0 | active | — | — |

## Workarounds

1. **Document the invalid TST (read at 24h) as 'uninterpretable' in the EHR. Order a new TST and schedule a return visit at 48-72 hours. Provide patient with written instructions: 'Do not read the test yourself; return to clinic exactly 48-72 hours after placement.'** (95% success)
   ```
   Document the invalid TST (read at 24h) as 'uninterpretable' in the EHR. Order a new TST and schedule a return visit at 48-72 hours. Provide patient with written instructions: 'Do not read the test yourself; return to clinic exactly 48-72 hours after placement.'
   ```
2. **If the patient cannot return, switch to IGRA (QuantiFERON-TB Gold Plus) as a single-visit alternative. Order in EHR: 'IGRA for LTBI screening, reason: TST reading window missed.'** (90% success)
   ```
   If the patient cannot return, switch to IGRA (QuantiFERON-TB Gold Plus) as a single-visit alternative. Order in EHR: 'IGRA for LTBI screening, reason: TST reading window missed.'
   ```
3. **Implement a hard stop in the nursing documentation system: if TST reading time is <48 hours, block finalization and display: 'TST reading invalid: must be 48-72 hours after placement. Re-enter time or order repeat test.'** (85% success)
   ```
   Implement a hard stop in the nursing documentation system: if TST reading time is <48 hours, block finalization and display: 'TST reading invalid: must be 48-72 hours after placement. Re-enter time or order repeat test.'
   ```

## Dead Ends

- **** — The test must be read within the 48-72 hour window; a 24-hour reading is invalid and cannot be 'corrected' by a later reading because the induration may have already peaked and subsided. (80% fail)
- **** — Chest X-ray is not a substitute for TST; it detects active disease, not latent infection. A negative X-ray does not rule out latent TB. (75% fail)
- **** — IGRA is an alternative, but the invalid TST should be documented and the patient informed; IGRA may not be covered by insurance if TST was already performed. (60% fail)