Medplum

# BMI Calculation Bot This bot processes a Patient resource and automatically calculates BMI (Body Mass Index) from the latest height and weight observations. ## Overview The bot performs the following operations: 1. **Searches for observations**: - Latest height observation (LOINC: 8302-2) - Latest weight observation (LOINC: 29463-7) 2. **Calculates BMI**: - Extracts values from the latest height and weight observations - Handles unit conversions automatically - Calculates BMI using the formula: `BMI = weight (kg) / (height (m))²` 3. **Creates BMI Observation**: - Creates a new BMI observation (LOINC: 39156-5) each time the bot runs - Stores the calculated BMI value in kg/m² - Allows tracking BMI changes over time ## Unit Conversions The bot automatically handles unit conversions for both height and weight: ### Height Conversions: - **Centimeters (cm)** → Meters (m): divides by 100 - **Inches (in)** → Meters (m): multiplies by 0.0254 - **Meters (m)** → No conversion needed ### Weight Conversions: - **Grams (g)** → Kilograms (kg): divides by 1000 - **Pounds (lb)** → Kilograms (kg): multiplies by 0.453592 - **Ounces (oz)** → Kilograms (kg): multiplies by 0.0283495 - **Kilograms (kg)** → No conversion needed ## Setup 1. Create a Bot resource and paste the bot code from `bmi-calculation-bot.ts` 2. Configure the bot subscription to trigger on `Patient` resource creation or update 3. Ensure the bot has appropriate access permissions for: - Reading `Patient` resources - Searching `Observation` resources - Creating/updating `Observation` resources ## Usage 1. Ensure the patient has at least one height observation and one weight observation 2. When the patient resource is created or updated, the bot will: - Find the latest height and weight observations - Calculate BMI from those values - Create a new BMI observation (preserves historical BMI values) ## Behavior - **If height or weight observation is missing**: The bot logs a message and exits without creating a BMI observation - **If observation values are missing**: The bot logs a message and exits - **If BMI calculation succeeds**: The bot creates a new BMI observation with the calculated value (allows tracking BMI over time) ## Example Given a patient with: - Latest height observation: 70 inches (converted to 1.778 meters) - Latest weight observation: 180 pounds (converted to 81.647 kg) The bot will calculate: ``` BMI = 81.647 kg / (1.778 m)² = 25.85 kg/m² ``` And create an Observation with: - Code: LOINC 39156-5 (Body mass index) - Value: 25.85 kg/m² - Status: final - Category: vital-signs ## Notes - The bot uses the **latest** observation of each type (sorted by date) - BMI observations are **created** (not upserted), allowing you to track BMI changes over time - Each time the bot runs, it creates a new BMI observation based on the latest height and weight - The bot handles common unit variations but may log warnings for unrecognized units