82 lines
3.1 KiB
JavaScript
82 lines
3.1 KiB
JavaScript
var bmiCache = null;
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export function loadBmiLmsData() {
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if (bmiCache) return Promise.resolve(bmiCache);
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return fetch('/data/calculators/bmi-lms.json', { credentials: 'same-origin' })
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.then(function(response) {
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if (!response.ok) throw new Error('Failed to load BMI LMS data');
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return response.json();
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})
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.then(function(data) {
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bmiCache = data.lms || {};
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return bmiCache;
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});
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}
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export function interpolateLMS(lmsTable, val) {
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var keys = Object.keys(lmsTable).map(Number).sort(function(a,b){return a-b;});
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if (val <= keys[0]) return lmsTable[keys[0]];
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if (val >= keys[keys.length-1]) return lmsTable[keys[keys.length-1]];
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for (var i = 0; i < keys.length - 1; i++) {
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if (val >= keys[i] && val <= keys[i+1]) {
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var t = (val - keys[i]) / (keys[i+1] - keys[i]);
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var a = lmsTable[keys[i]], b = lmsTable[keys[i+1]];
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return { L: a.L + t*(b.L-a.L), M: a.M + t*(b.M-a.M), S: a.S + t*(b.S-a.S) };
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}
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}
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return lmsTable[keys[0]];
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}
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function normalCDF(z) {
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var a1=0.254829592, a2=-0.284496736, a3=1.421413741, a4=-1.453152027, a5=1.061405429, p=0.3275911;
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var sign = z < 0 ? -1 : 1;
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z = Math.abs(z) / Math.sqrt(2);
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var t = 1 / (1 + p * z);
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var y = 1 - (((((a5*t+a4)*t)+a3)*t+a2)*t+a1)*t*Math.exp(-z*z);
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return 0.5 * (1 + sign * y);
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}
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export function calcBMIPercentile(bmi, L, M, S) {
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var z;
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if (Math.abs(L) < 0.001) z = Math.log(bmi / M) / S;
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else z = (Math.pow(bmi / M, L) - 1) / (L * S);
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var p = normalCDF(z);
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return { z: z, percentile: Math.round(p * 10000) / 100 };
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}
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export function valueFromLMS(L, M, S, z) {
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if (Math.abs(L) < 0.001) return M * Math.exp(S * z);
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return M * Math.pow(1 + L * S * z, 1 / L);
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}
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export function classifyBMI(percentile, bmi, lms) {
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var bmi95 = valueFromLMS(lms.L, lms.M, lms.S, 1.645);
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var pctOf95 = (bmi / bmi95) * 100;
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if (percentile >= 95) {
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if (pctOf95 >= 140) return { text: 'Class 3 Severe Obesity', color: '#7f1d1d', bg: '#fecaca', pctOf95: pctOf95, bmi95: bmi95 };
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if (pctOf95 >= 120) return { text: 'Class 2 Severe Obesity', color: '#dc2626', bg: '#fee2e2', pctOf95: pctOf95, bmi95: bmi95 };
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return { text: 'Obese (Class 1)', color: '#ef4444', bg: '#fee2e2', pctOf95: pctOf95, bmi95: bmi95 };
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}
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if (percentile >= 85) return { text: 'Overweight', color: '#f97316', bg: '#ffedd5', pctOf95: pctOf95, bmi95: bmi95 };
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if (percentile >= 5) return { text: 'Healthy Weight', color: '#10b981', bg: '#d1fae5', pctOf95: pctOf95, bmi95: bmi95 };
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return { text: 'Underweight', color: '#f59e0b', bg: '#fef3c7', pctOf95: pctOf95, bmi95: bmi95 };
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}
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export function calculateBMIAssessment(lmsData, sex, ageYears, weightKg, heightCm) {
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var bmi = weightKg / Math.pow(heightCm / 100, 2);
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var ageMonths = Math.round(ageYears * 12);
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if (ageMonths < 24) ageMonths = 24;
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if (ageMonths > 240) ageMonths = 240;
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var lms = interpolateLMS(lmsData[sex], ageMonths);
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var result = calcBMIPercentile(bmi, lms.L, lms.M, lms.S);
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var classification = classifyBMI(result.percentile, bmi, lms);
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return {
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ageMonths: ageMonths,
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bmi: bmi,
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z: result.z,
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percentile: result.percentile,
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lms: lms,
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classification: classification
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};
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}
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