bmi-bsa-calculator

# BMI & BSA Calculator

## Overview

Clinical calculator for anthropometric measurements used in health assessment, obesity screening, and chemotherapy dosing calculations.

**Key Capabilities:**
- **BMI Calculation**: Standard and adjusted BMI formulas
- **BSA Estimation**: Multiple validated formulas (DuBois, Mosteller, Haycock)
- **Weight Classification**: WHO and CDC category assignment
- **Dosing Support**: Chemotherapy and medication dose calculations
- **Pediatric Support**: Age-appropriate norms and calculations
- **Unit Flexibility**: Metric and imperial input support

## When to Use

**✅ Use this skill when:**
- Calculating chemotherapy doses requiring BSA (mg/m²)
- Screening for obesity or underweight in clinical practice
- Adjusting drug doses based on body composition
- Documenting baseline anthropometrics in patient charts
- Teaching medical students clinical calculations
- Quick assessment in resource-limited settings

**❌ Do NOT use when:**
- BMI alone for clinical diagnosis → Use comprehensive metabolic assessment
- Pregnancy weight assessment → Use gestational weight gain charts
- Pediatric growth evaluation → Use WHO/CDC growth charts with percentiles
- Body composition analysis → Use DEXA or bioimpedance
- Athletic/muscular patients → Consider body fat % instead of BMI

**Integration:**
- **Upstream**: `ehr-semantic-compressor` (patient data extraction), `automated-soap-note-generator` (vital signs)
- **Downstream**: `drug-interaction-checker` (dose calculation), `medication-reconciliation` (dosing verification)

## Core Capabilities

### 1. BMI Calculation

Calculate Body Mass Index with classification:

```python
from scripts.calculator import BMIBSACalculator

calc = BMIBSACalculator()

# Calculate BMI
result = calc.calculate_bmi(
    weight_kg=70,
    height_cm=175,
    age=45,
    sex="male"
)

print(f"BMI: {result.bmi:.1f} kg/m²")
print(f"Category: {result.category}")  # Normal weight
print(f"Ideal weight range: {result.ideal_weight_range}")
```

**BMI Categories (WHO):**
| Category | BMI Range | Clinical Significance |
|----------|-----------|---------------------|
| **Underweight** | < 18.5 | Malnutrition risk |
| **Normal** | 18.5 - 24.9 | Healthy range |
| **Overweight** | 25.0 - 29.9 | Increased risk |
| **Obese I** | 30.0 - 34.9 | High risk |
| **Obese II** | 35.0 - 39.9 | Very high risk |
| **Obese III** | ≥ 40.0 | Extremely high risk |

**Adjusted BMI:**
- **BMI Prime**: BMI / 25 (obesity severity index)
- **Ponderal Index**: BMI for tall/short individuals
- **Age-adjusted**: For elderly patients (>65)

### 2. BSA Calculation

Multiple formulas for different clinical scenarios:

```python
# Calculate BSA using different formulas
bsa_results = calc.calculate_bsa(
    weight_kg=70,
    height_cm=175,
    formulas=["dubois", "mosteller", "haycock", "gehan_george"]
)

for formula, bsa in bsa_results.items():
    print(f"{formula}: {bsa:.2f} m²")
```

**BSA Formulas:**
| Formula | Equation | Best For |
|---------|----------|----------|
| **DuBois** | 0.007184 × W^0.425 × H^0.725 | Adults (most common) |
| **Mosteller** | √(W × H / 3600) | Adults (simplified) |
| **Haycock** | 0.024265 × W^0.5378 × H^0.3964 | Pediatrics |
| **Gehan-George** | 0.0235 × W^0.51456 × H^0.42246 | Oncology |
| **Yu** | 0.015925 × W^0.5 × H^0.5 | Asian populations |

### 3. Drug Dosing Calculations

Apply BSA to medication dosing:

```python
# Calculate chemotherapy dose
dose = calc.calculate_dose(
    bsa=bsa_results["dubois"],
    drug="carboplatin",
    dose_per_m2=400,  # mg/m²
    max_dose=800  # mg cap
)

print(f"Calculated dose: {dose:.0f} mg")
print(f"BSA used: {bsa_results['dubois']:.2f} m²")
```

**Common BSA-Based Doses:**
- Carboplatin: AUC-based (Calvert formula)
- 5-FU: 400-600 mg/m²
- Doxorubicin: 60-75 mg/m² (lifetime max 450-550 mg/m²)
- Paclitaxel: 135-175 mg/m²

### 4. Pediatric Calculations

Age-appropriate calculations for children:

```python
pediatric = calc.pediatric_mode(
    weight_kg=25,
    height_cm=120,
    age_years=8,
    sex="female"
)

print(f"BMI-for-age percentile: {pediatric.bmi_percentile}%")
print(f"Weight status: {pediatric.weight_status}")
print(f"BSA (Haycock): {pediatric.bsa:.2f} m²")
```

**Pediatric Considerations:**
- BMI percentiles (not absolute values)
- Growth chart integration
- Age-specific BSA formulas
- Body composition changes with development

## Common Patterns

### Pattern 1: Chemotherapy Dosing

**Scenario**: Calculate carboplatin dose for cancer patient.

```bash
# Calculate BSA and dose
python scripts/main.py \
  --weight 70 \
  --height 175 \
  --drug carboplatin \
  --target-auc 5 \
  --creatinine-clearance 80 \
  --output dose_calculation.txt
```

**Output:**
```
BSA (DuBois): 1.79 m²
Calvert Formula: Dose = Target AUC × (GFR + 25)
                 = 5 × (80 + 25)
                 = 525 mg
Maximum dose check: 525 mg ≤ 800 mg ✓
Recommended dose: 525 mg
```

### Pattern 2: Obesity Screening

**Scenario**: BMI assessment for weight management clinic.

```python
# BMI with full assessment
assessment = calc.assess_bmi(
    weight_kg=95,
    height_cm=165,
    age=52,
    sex="female",
    waist_cm=98
)

print(f"BMI: {assessment.bmi:.1f} (Obese Class II)")
print(f"Waist-to-height ratio: {assessment.whtr:.2f} (High risk)")
print(f"Comorbidity risk: {assessment.health_risk}")
print(f"Recommended: {assessment.recommendations}")
```

### Pattern 3: Pediatric Growth Assessment

**Scenario**: Calculate child's BSA for medication dosing.

```python
# Pediatric dosing
child = calc.pediatric_assessment(
    weight_kg=20,
    height_cm=110,
    age_years=6,
    sex="male"
)

print(f"BSA: {child.bsa:.2f} m² (Haycock formula)")
print(f"BMI percentile: {child.bmi_percentile}th")
print(f"Doxorubicin dose: {child.bsa * 60:.0f} mg")
```

### Pattern 4: Rapid Clinical Assessment

**Scenario**: Quick BMI/BSA for admission vital signs.

```bash
# Quick calculation
python scripts/main.py --weight 80 --height 180 --quick

# Output:
# BMI: 24.7 kg/m² (Normal)
# BSA: 2.00 m² (DuBois)
# Ideal weight: 65-80 kg
```

## Complete Workflow Example

**Comprehensive patient assessment:**

```python
from scripts.calculator import BMIBSACalculator
from scripts.reports import ClinicalReport

# Initialize
calc = BMIBSACalculator()
report = ClinicalReport()

# Patient data
patient = {
    "weight_kg": 75,
    "height_cm": 170,
    "age": 55,
    "sex": "female",
    "waist_cm": 88
}

# Calculate all metrics
bmi = calc.calculate_bmi(**patient)
bsa = calc.calculate_bsa(**patient, formula="dubois")
assessment = calc.comprehensive_assessment(**patient)

# Generate report
report_data = {
    "bmi": bmi,
    "bsa": bsa,
    "assessment": assessment,
    "recommendations": assessment.recommendations
}

report.generate(report_data, output="patient_assessment.pdf")
```

## Quality Checklist

**Input Validation:**
- [ ] Weight realistic (2-300 kg range)
- [ ] Height realistic (50-250 cm range)
- [ ] Units clearly specified (kg/lbs, cm/in)
- [ ] Age appropriate for formulas used

**Calculation Accuracy:**
- [ ] Formula selection appropriate for patient
- [ ] BSA formula matches clinical context
- [ ] Pediatric vs. adult norms correctly applied
- [ ] Rounding appropriate (1-2 decimal places)

**Clinical Interpretation:**
- [ ] **CRITICAL**: BMI is screening tool, not diagnostic
- [ ] Ethnicity-specific cutoffs considered
- [ ] Muscle mass considered (athletes)
- [ ] Age adjustments applied (elderly/children)

**Documentation:**
- [ ] Formula used documented (DuBois vs. Mosteller)
- [ ] Units clearly stated
- [ ] Date of calculation recorded
- [ ] Dose limits verified for chemotherapy

## Common Pitfalls

**Calculation Errors:**
- ❌ **Unit confusion** → Pounds vs. kg, inches vs. cm
  - ✅ Always verify units; convert if necessary

- ❌ **Wrong formula** → Using adult BSA for infants
  - ✅ Use Haycock for children < 12 years

- ❌ **BMI over-interpretation** → Diagnosing based on BMI alone
  - ✅ BMI is screening tool; clinical correlation required

**Clinical Misuse:**
- ❌ **Athletes misclassified** → Muscular patients marked obese
  - ✅ Consider waist circumference or body fat %

- ❌ **Elderly inappropriate norms** → Same cutoffs for all ages
  - ✅ Use age-adjusted BMI for >65 years

- ❌ **Ignoring ethnicity** → Universal cutoffs applied
  - ✅ Asian populations: lower obesity thresholds

**Dosing Errors:**
- ❌ **BSA rounding** → 1.79 m² rounded to 1.8 m²
  - ✅ Use precise values for chemotherapy

- ❌ **Max dose ignored** → Exceeding lifetime limits
  - ✅ Always check cumulative doses (doxorubicin)

## References

Available in `references/` directory:

- `bsa_formulas_comparison.md` - Formula accuracy by population
- `pediatric_norms.md` - Growth charts and percentiles
- `chemotherapy_dosing.md` - BSA-based drug calculations
- `ethnic_adjustments.md` - Population-specific cutoffs
- `calculator_validation.md` - Comparison with reference standards

## Scripts

Located in `scripts/` directory:

- `main.py` - CLI calculator interface
- `calculator.py` - Core BMI/BSA calculations
- `formulas.py` - Multiple BSA formula implementations
- `pediatric.py` - Child-specific calculations
- `dosing.py` - Medication dose calculations
- `reports.py` - Clinical report generation

## Limitations

- **BMI Limitations**: Doesn't distinguish fat from muscle; varies by ethnicity
- **BSA Estimation**: All formulas are approximations; 10-15% variation normal
- **Extreme Values**: Very short/tall patients may have inaccurate estimates
- **Not for Diagnosis**: BMI/BSA are tools, not clinical diagnoses
- **Amputees**: Standard formulas inaccurate; adjustment needed
- **Pregnancy**: Special considerations not included

## Parameters

| Parameter | Type | Default | Required | Description |
|-----------|------|---------|----------|-------------|
| `--weight`, `-w` | float | - | Yes | Weight in kilograms |
| `--height`, `-H` | float | - | Yes | Height in centimeters |
| `--dose`, `-d` | float | - | No | Standard drug dose per m² in mg (optional) |
| `--format`, `-f` | string | text | No | Output format (text, json) |
| `--output`, `-o` | string | - | No | Output file path (optional) |

## Usage

### Basic Usage

```bash
# Calculate BMI and BSA
python scripts/main.py --weight 70 --height 175

# Calculate with drug dosing
python scripts/main.py --weight 70 --height 175 --dose 100

# Output as JSON
python scripts/main.py --weight 70 --height 175 --format json --output results.json
```

## Risk Assessment

| Risk Indicator | Assessment | Level |
|----------------|------------|-------|
| Code Execution | Python script executed locally | Low |
| Network Access | No external API calls | Low |
| File System Access | Optional file output only | Low |
| Data Exposure | No sensitive data stored | Low |
| Clinical Risk | Results used for medical decisions | Medium |

## Security Checklist

- [x] No hardcoded credentials or API keys
- [x] No unauthorized file system access
- [x] Input validation for weight/height
- [x] Output does not expose sensitive information
- [x] Error messages sanitized
- [x] Script execution in sandboxed environment

## Prerequisites

```bash
# Python 3.7+
# No additional packages required (uses standard library)
```

## Evaluation Criteria

### Success Metrics
- [x] Successfully calculates BMI using standard formula
- [x] Successfully calculates BSA using DuBois formula
- [x] Correctly categorizes BMI (Underweight, Normal, Overweight, Obese)
- [x] Calculates drug doses based on BSA when provided

### Test Cases
1. **Normal Adult**: 70kg, 175cm → BMI 22.9 (Normal), BSA ~1.85 m²
2. **Drug Dosing**: 70kg, 175cm, 100mg/m² → Dose 185mg
3. **JSON Output**: Valid JSON with all fields

## Lifecycle Status

- **Current Stage**: Draft
- **Next Review Date**: 2026-03-06
- **Known Issues**: None
- **Planned Improvements**:
  - Add additional BSA formulas (Haycock, Mosteller)
  - Add pediatric BMI percentiles
  - Add unit conversion (lbs, ft/in)

---

**⚕️ Clinical Note: BMI and BSA are screening and calculation tools, not substitutes for clinical judgment. Always correlate with physical examination, patient history, and other assessments. Double-check all chemotherapy calculations independently.**