Calculating Bmi with Amputation

Amputee BMI Calculator

None / Full Body Hand (0.7%) Forearm (1.6%) Upper Arm (2.7%) Entire Arm (5.0%) Foot (1.5%) Below the Knee / Lower Leg (5.9%) Above the Knee / Upper Leg (10.1%) Entire Leg (16.0%)

Note: Percentages based on Osterkamp's standardized data for limb weight.

Calculation Results

Estimated Total Body Weight (ETBW): — kg

Adjusted BMI: —

Category: —

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Understanding BMI for Amputees

Body Mass Index (BMI) is a standard screening tool used to categorize weight status. However, for individuals with limb loss, the standard BMI formula is inaccurate because it doesn't account for the missing mass of the limb. To get a clinically relevant result, we must calculate the Estimated Total Body Weight (ETBW) before applying the BMI formula.

How the Calculation Works

Healthcare professionals use the Osterkamp formula to adjust weight based on the percentage of total body weight that the missing limb would normally represent. The formula for Estimated Total Body Weight is:

ETBW = Current Weight / (1 – Percentage of Missing Limb)

Once the ETBW is determined, we use the standard BMI formula: Weight (kg) / [Height (m)]².

Standard Limb Weight Percentages

• Entire Arm: 5.0%
• Upper Arm: 2.7%
• Forearm: 1.6%
• Hand: 0.7%
• Entire Leg: 16.0%
• Above the Knee (AKA): 10.1%
• Below the Knee (BKA): 5.9%
• Foot: 1.5%

Example Calculation

If an individual weighs 70kg, is 180cm tall, and has a below-the-knee amputation (5.9%):

1. Weight Adjustment: 70 / (1 – 0.059) = 74.39 kg (Estimated Total Body Weight).
2. BMI Calculation: 74.39 / (1.8 * 1.8) = 22.96.
3. Result: This individual falls into the "Healthy Weight" category.

Important Considerations

While the adjusted BMI provides a better estimate than the standard formula, it still has limitations. BMI does not distinguish between muscle mass and fat mass. Individuals with limb loss may experience changes in body composition, such as muscle atrophy in the residual limb or increased muscle mass in other areas due to mobility adaptations. Always consult with a healthcare provider or a registered dietitian for a comprehensive nutritional assessment.

function calculateAmputeeBMI() { var weight = parseFloat(document.getElementById("currentWeight").value); var heightCm = parseFloat(document.getElementById("currentHeight").value); var limbPercentage = parseFloat(document.getElementById("amputationType").value); if (!weight || !heightCm || weight <= 0 || heightCm <= 0) { alert("Please enter valid weight and height values."); return; } // Step 1: Calculate Estimated Total Body Weight (ETBW) // ETBW = Actual Weight / (1 – % loss) var etbw = weight / (1 – limbPercentage); // Step 2: Calculate BMI using ETBW // BMI = Weight(kg) / Height(m)^2 var heightM = heightCm / 100; var bmi = etbw / (heightM * heightM); // Determine Category var category = ""; var color = "#333"; if (bmi = 18.5 && bmi = 25 && bmi < 29.9) { category = "Overweight"; color = "#f1c40f"; } else { category = "Obese"; color = "#e74c3c"; } // Display Results document.getElementById("resETBW").innerText = etbw.toFixed(2); document.getElementById("resBMI").innerText = bmi.toFixed(2); document.getElementById("resCategory").innerText = category; document.getElementById("resCategory").style.color = color; document.getElementById("bmiResultWrapper").style.display = "block"; // Smooth scroll to result document.getElementById("bmiResultWrapper").scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }