# AI instructs a diabetic patient to use U-40 insulin syringe for U-100 insulin, causing tenfold dosing error

- **ID:** `medical/insulin-mix-up-u40-u100`
- **Domain:** medical
- **Category:** runtime_error
- **Error Code:** `INSULIN_MIXUP_U40_U100`
- **Verification:** ai_generated
- **Fix Rate:** 90%

## Root Cause

U-40 (40 units/mL) and U-100 (100 units/mL) insulins require matched syringes; using a U-40 syringe for U-100 insulin delivers 2.5x the intended dose per unit mark, risking severe hypoglycemia.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| insulin:Humulin-R-U100-2024 | active | — | — |
| insulin:Novolin-N-U40-2023 | active | — | — |

## Workarounds

1. **Always verify the insulin concentration (U-40 or U-100) on the vial label and match it with the syringe barrel marking. Use only syringes explicitly labeled for that concentration. For U-100 insulin, use only U-100 syringes. For U-40 insulin, use only U-40 syringes. If unsure, discard and obtain correct syringe.** (95% success)
   ```
   Always verify the insulin concentration (U-40 or U-100) on the vial label and match it with the syringe barrel marking. Use only syringes explicitly labeled for that concentration. For U-100 insulin, use only U-100 syringes. For U-40 insulin, use only U-40 syringes. If unsure, discard and obtain correct syringe.
   ```
2. **If only a U-40 syringe is available for U-100 insulin, calculate the correct volume: divide desired insulin units by 2.5. For example, to deliver 10 units of U-100 insulin, draw to the '4 unit' mark on a U-40 syringe (10 / 2.5 = 4). Document this calculation clearly and double-check with a second person.** (85% success)
   ```
   If only a U-40 syringe is available for U-100 insulin, calculate the correct volume: divide desired insulin units by 2.5. For example, to deliver 10 units of U-100 insulin, draw to the '4 unit' mark on a U-40 syringe (10 / 2.5 = 4). Document this calculation clearly and double-check with a second person.
   ```
3. **Use insulin pens instead of syringes where possible; pens are pre-filled with the correct concentration and eliminate syringe mismatch errors.** (90% success)
   ```
   Use insulin pens instead of syringes where possible; pens are pre-filled with the correct concentration and eliminate syringe mismatch errors.
   ```

## Dead Ends

- **Assuming all insulin syringes are interchangeable if they have the same needle gauge** — Needle gauge does not indicate concentration; the syringe barrel is calibrated for a specific concentration (U-40 vs U-100). Using wrong barrel causes volumetric mismatch. (60% fail)
- **Relying on memory or visual estimate of 'units' without checking syringe label** — Unit markings on U-40 and U-100 syringes look similar but represent different volumes; a '10 unit' mark on U-40 syringe delivers 0.25 mL, while on U-100 it delivers 0.1 mL. (70% fail)
- **Believing that a conversion chart is unnecessary because the patient 'always uses the same syringe'** — Patients may receive different insulin types (e.g., switching from animal to human insulin) requiring different concentrations, but continue using old syringes. (50% fail)