Name: healthcare-cdss-patterns
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Healthcare CDSS Development Patterns
Patterns for building Clinical Decision Support Systems that integrate into EMR workflows. CDSS modules are patient safety critical — zero tolerance for false negatives.
When to Use
Implementing drug interaction checking
Building dose validation engines
Implementing clinical scoring systems (NEWS2, qSOFA, APACHE, GCS)
Designing alert systems for abnormal clinical values
Building medication order entry with safety checks
Integrating lab result interpretation with clinical context
How It Works
The CDSS engine is a
pure function library with zero side effects
. Input clinical data, output alerts. This makes it fully testable.
Three primary modules:
checkInteractions(newDrug, currentMeds, allergies)
— Checks a new drug against current medications and known allergies. Returns severity-sorted
InteractionAlert[]
. Uses
DrugInteractionPair
data model.
validateDose(drug, dose, route, weight, age, renalFunction)
— Validates a prescribed dose against weight-based, age-adjusted, and renal-adjusted rules. Returns
DoseValidationResult
.
calculateNEWS2(vitals)
— National Early Warning Score 2 from
NEWS2Input
. Returns
NEWS2Result
with total score, risk level, and escalation guidance.
EMR UI
↓ (user enters data)
CDSS Engine (pure functions, no side effects)
├── Drug Interaction Checker
├── Dose Validator
├── Clinical Scoring (NEWS2, qSOFA, etc.)
└── Alert Classifier
↓ (returns alerts)
EMR UI (displays alerts inline, blocks if critical)
Drug Interaction Checking
interface
DrugInteractionPair
{
drugA
:
string
;
// generic name
drugB
:
string
;
// generic name
severity
:
'critical'
|
'major'
|
'minor'
;
mechanism
:
string
;
clinicalEffect
:
string
;
recommendation
:
string
;
}
function
checkInteractions
(
newDrug
:
string
,
currentMedications
:
string
[
]
,
allergyList
:
string
[
]
)
:
InteractionAlert
[
]
{
if
(
!
newDrug
)
return
[
]
;
const
alerts
:
InteractionAlert
[
]
=
[
]
;
for
(
const
current
of
currentMedications
)
{
const
interaction
=
findInteraction
(
newDrug
,
current
)
;
if
(
interaction
)
{
alerts
.
push
(
{
severity
:
interaction
.
severity
,
pair
:
[
newDrug
,
current
]
,
message
:
interaction
.
clinicalEffect
,
recommendation
:
interaction
.
recommendation
}
)
;
}
}
for
(
const
allergy
of
allergyList
)
{
if
(
isCrossReactive
(
newDrug
,
allergy
)
)
{
alerts
.
push
(
{
severity
:
'critical'
,
pair
:
[
newDrug
,
allergy
]
,
message
:
`
Cross-reactivity with documented allergy:
${
allergy
}
`
,
recommendation
:
'Do not prescribe without allergy consultation'
}
)
;
}
}
return
alerts
.
sort
(
(
a
,
b
)
=>
severityOrder
(
a
.
severity
)
-
severityOrder
(
b
.
severity
)
)
;
}
Interaction pairs must be
bidirectional: if Drug A interacts with Drug B, then Drug B interacts with Drug A. Dose Validation interface DoseValidationResult { valid : boolean ; message : string ; suggestedRange : { min : number ; max : number ; unit : string } | null ; factors : string [ ] ; } function validateDose ( drug : string , dose : number , route : 'oral' | 'iv' | 'im' | 'sc' | 'topical' , patientWeight ? : number , patientAge ? : number , renalFunction ? : number ) : DoseValidationResult { const rules = getDoseRules ( drug , route ) ; if ( ! rules ) return { valid : true , message : 'No validation rules available' , suggestedRange : null , factors : [ ] } ; const factors : string [ ] = [ ] ; // SAFETY: if rules require weight but weight missing, BLOCK (not pass) if ( rules . weightBased ) { if ( ! patientWeight || patientWeight <= 0 ) { return { valid : false , message : Weight required for ${ drug } (mg/kg drug) , suggestedRange : null , factors : [ 'weight_missing' ] } ; } factors . push ( 'weight' ) ; const maxDose = rules . maxPerKg * patientWeight ; if ( dose

maxDose ) { return { valid : false , message : Dose exceeds max for ${ patientWeight } kg , suggestedRange : { min : rules . minPerKg * patientWeight , max : maxDose , unit : rules . unit } , factors } ; } } // Age-based adjustment (when rules define age brackets and age is provided) if ( rules . ageAdjusted && patientAge !== undefined ) { factors . push ( 'age' ) ; const ageMax = rules . getAgeAdjustedMax ( patientAge ) ; if ( dose

ageMax ) { return { valid : false , message : Exceeds age-adjusted max for ${ patientAge } yr , suggestedRange : { min : rules . typicalMin , max : ageMax , unit : rules . unit } , factors } ; } } // Renal adjustment (when rules define eGFR brackets and eGFR is provided) if ( rules . renalAdjusted && renalFunction !== undefined ) { factors . push ( 'renal' ) ; const renalMax = rules . getRenalAdjustedMax ( renalFunction ) ; if ( dose

renalMax ) { return { valid : false , message : Exceeds renal-adjusted max for eGFR ${ renalFunction } , suggestedRange : { min : rules . typicalMin , max : renalMax , unit : rules . unit } , factors } ; } } // Absolute max if ( dose

rules . absoluteMax ) { return { valid : false , message : Exceeds absolute max ${ rules . absoluteMax } ${ rules . unit } , suggestedRange : { min : rules . typicalMin , max : rules . absoluteMax , unit : rules . unit } , factors : [ ... factors , 'absolute_max' ] } ; } return { valid : true , message : 'Within range' , suggestedRange : { min : rules . typicalMin , max : rules . typicalMax , unit : rules . unit } , factors } ; } Clinical Scoring: NEWS2 interface NEWS2Input { respiratoryRate : number ; oxygenSaturation : number ; supplementalOxygen : boolean ; temperature : number ; systolicBP : number ; heartRate : number ; consciousness : 'alert' | 'voice' | 'pain' | 'unresponsive' ; } interface NEWS2Result { total : number ; // 0-20 risk : 'low' | 'low-medium' | 'medium' | 'high' ; components : Record < string , number

; escalation : string ; } Scoring tables must match the Royal College of Physicians specification exactly. Alert Severity and UI Behavior Severity UI Behavior Clinician Action Required Critical Block action. Non-dismissable modal. Red. Must document override reason to proceed Major Warning banner inline. Orange. Must acknowledge before proceeding Minor Info note inline. Yellow. Awareness only, no action required Critical alerts must NEVER be auto-dismissed or implemented as toast notifications. Override reasons must be stored in the audit trail. Testing CDSS (Zero Tolerance for False Negatives) describe ( 'CDSS — Patient Safety' , ( ) => { INTERACTION_PAIRS . forEach ( ( { drugA , drugB , severity } ) => { it ( detects ${ drugA } + ${ drugB } ( ${ severity } ) , ( ) => { const alerts = checkInteractions ( drugA , [ drugB ] , [ ] ) ; expect ( alerts . length ) . toBeGreaterThan ( 0 ) ; expect ( alerts [ 0 ] . severity ) . toBe ( severity ) ; } ) ; it ( detects ${ drugB } + ${ drugA } (reverse) , ( ) => { const alerts = checkInteractions ( drugB , [ drugA ] , [ ] ) ; expect ( alerts . length ) . toBeGreaterThan ( 0 ) ; } ) ; } ) ; it ( 'blocks mg/kg drug when weight is missing' , ( ) => { const result = validateDose ( 'gentamicin' , 300 , 'iv' ) ; expect ( result . valid ) . toBe ( false ) ; expect ( result . factors ) . toContain ( 'weight_missing' ) ; } ) ; it ( 'handles malformed drug data gracefully' , ( ) => { expect ( ( ) => checkInteractions ( '' , [ ] , [ ] ) ) . not . toThrow ( ) ; } ) ; } ) ; Pass criteria: 100%. A single missed interaction is a patient safety event. Anti-Patterns Making CDSS checks optional or skippable without documented reason Implementing interaction checks as toast notifications Using any types for drug or clinical data Hardcoding interaction pairs instead of using a maintainable data structure Silently catching errors in CDSS engine (must surface failures loudly) Skipping weight-based validation when weight is not available (must block, not pass) Examples Example 1: Drug Interaction Check const alerts = checkInteractions ( 'warfarin' , [ 'aspirin' , 'metformin' ] , [ 'penicillin' ] ) ; // [{ severity: 'critical', pair: ['warfarin', 'aspirin'], // message: 'Increased bleeding risk', recommendation: 'Avoid combination' }] Example 2: Dose Validation const ok = validateDose ( 'paracetamol' , 1000 , 'oral' , 70 , 45 ) ; // { valid: true, suggestedRange: { min: 500, max: 4000, unit: 'mg' } } const bad = validateDose ( 'paracetamol' , 5000 , 'oral' , 70 , 45 ) ; // { valid: false, message: 'Exceeds absolute max 4000mg' } const noWeight = validateDose ( 'gentamicin' , 300 , 'iv' ) ; // { valid: false, factors: ['weight_missing'] } Example 3: NEWS2 Scoring const result = calculateNEWS2 ( { respiratoryRate : 24 , oxygenSaturation : 93 , supplementalOxygen : true , temperature : 38.5 , systolicBP : 100 , heartRate : 110 , consciousness : 'voice' } ) ; // { total: 13, risk: 'high', escalation: 'Urgent clinical review. Consider ICU.' }

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