Hazard¶

DO NOT EDIT BELOW THIS LINE UNLESS YOU KNOW WHAT YOU ARE DOING

Hazard name¶

Incorrect age calculation

General utility label¶

[2]

Likelihood scoring¶

TBC

Severity scoring¶

TBC

Description¶

Age calculation logic does not correctly handle edge cases including same-day birthdays, leap years, and timezone differences between server (UTC) and browser (local time).

Causes¶

Month/day comparison logic error in date calculations
Timezone mismatch between server birthDate (UTC) and browser Date object (local time)
Leap year birthday on Feb 29th causing calculation error

Effect¶

Patient age displayed is incorrect (typically off by one year).

Hazard¶

Clinician makes age-inappropriate clinical decisions including drug dosage calculations, screening recommendations, and treatment protocols that are age-dependent.

Hazard type¶

IncorrectResult

Harm¶

Pediatric patient receives adult dosage causing toxicity, or elderly patient misses age-appropriate screening leading to delayed cancer diagnosis. Age-inappropriate medication dosage could cause serious injury or death.

Existing controls¶

None identified during initial analysis.

Assignment¶

Clinical Safety Officer

Labelling¶

TBC (awaiting scoring)

Project¶

Clinical Risk Management

Hazard controls¶

Design controls (manufacturer)¶

Replace custom age calculation with date-fns library differenceInYears() function which correctly handles all edge cases including leap years and timezone normalization. Parse birthDate as UTC using parseISO() before calculation.
Add unit tests covering edge cases: birthday today (expect current age), birthday tomorrow (expect current age), Feb 29 leap year birthday (expect correct age in non-leap years), timezone edge cases (UTC midnight vs local time).
Display age with calculation timestamp: "Age: 45 years (calculated from DOB 1979-02-15 at 2026-02-08 14:30)". Allows clinician to verify calculation freshness.
Add age validation warning: if calculated age <0 or >150 years, display red warning "Age calculation may be incorrect - verify DOB" and prevent high-risk actions until DOB manually verified.
Normalize all birthDate values to UTC midnight (00:00:00Z) in FHIR storage to eliminate timezone ambiguity. Store as YYYY-MM-DD string format without time component.

Testing controls (manufacturer)¶

Unit test: Patient with DOB 1980-01-01, test date 2026-02-08, assert age = 46 years. Patient with DOB 1980-02-09 (tomorrow), assert age = 45 years not 46.
Unit test: Patient born Feb 29, 2000 (leap year), test date Feb 28, 2026 (non-leap), assert age = 25 years. Test on Mar 1, 2026, assert age = 26 years.
Integration test: Mock system timezone as UTC, browser timezone as UTC+8, patient DOB 2000-01-01, assert age calculated identically in both timezones.
Unit test: Patient DOB in future (2027-01-01), test date 2026-02-08, assert age displays error warning not negative number. Patient DOB 1800-01-01, assert age >150 warning displays.

Training controls (deployment)¶

Train clinicians to verify age-dependent dosing calculations using multiple sources: check age displayed on screen, manually verify DOB, consult BNF or formulary for weight-based alternative if age seems incorrect.
Document workflow for pediatric dosing: "Always verify child's age by asking parent/guardian DOB and comparing to screen. If mismatch >1 year, update DOB in system before calculating drug dose."
Include age verification in clinical handover: "Patient age verified as [X] years, DOB [YYYY-MM-DD] checked against patient wristband/ID."

Business process controls (deployment)¶

NHS Trust pharmacy policy: Pharmacists must independently verify patient age against DOB before dispensing age-dependent medications (pediatric formulations, geriatric dose adjustments).
Clinical governance requirement: Age-based screening reminders (mammography at 50, colonoscopy at 55, PSA at 50) must include DOB verification step before sending invitation.
Incident reporting: Any age calculation error leading to wrong dosage or missed screening must be reported as clinical safety incident for root cause analysis.

Residual hazard risk assessment¶

TBC — awaiting initial controls implementation.

Hazard status¶

Draft from LLM

Code associated with hazard¶

frontend/src/pages/Home.tsx:140-151
frontend/src/pages/Patient.tsx:146-157