bmi_calc.php

<?php

$db = new PDO('mysql:host='.DB_HOST.';dbname='.DB_NAME, DB_USER, DB_PASSWORD);
$data_error = false;

/* /////// PATIENT VARS ///////////////////////////////////////////////////////////////////////// */

$patient_dob = '10/08/05';
$patient_sex = 'male';
$patient_weight = '60';
$patient_height = '4,0';
$date_measured = '2/13/13';

/* ////////////////////////////////////////////////////////////////////////////////////////////// */

$age_in_months = ((strtotime($date_measured)-strtotime($patient_dob))/(3600*24))/30.4375;
$height = explode(',',$patient_height); $height_inches = ($height[0]*12)+$height[1];
$bmi = ($patient_weight/(pow($height_inches,2)))*703.069006;
$bmi_category = 'Unknown';

if ($age_in_months >= 222) {

  $bmi_category = get_category_by_bmi($bmi);

} else {

	// CDC chart uses ages from 23.5 months to 240.5 months, in 1 month increments:
	$lookup_ages = array(); for ($i = 23; $i <=240; $i++) { $lookup_ages[] = $i+0.5; }	
	$closest_index = nearest_value($age_in_months,$lookup_ages);
	
	if ((strtolower($patient_sex)=='m') || (strtolower($patient_sex)=='male')) { $select_columns = 'MALE'; }
	else { $select_columns = 'FEMALE'; }
	
	$sth = $db->prepare("SELECT * FROM CDC_BMI WHERE AGE = ?");
	$sth->execute(array($closest_index));
	$result = $sth->fetch(PDO::FETCH_ASSOC);
	
	$l_index = $result[$select_columns.'_L'];
	$m_index = $result[$select_columns.'_M'];
	$s_index = $result[$select_columns.'_S'];
	
	$z_score = (pow(($bmi/$m_index),$l_index)-1)/($l_index*$s_index);
	$percentile = intval(normal_dist($z_score)*1000)/10;

	$lower_sd = ($m_index-($m_index*pow((1+$l_index*$s_index*(-2)),(1/$l_index))))/2;
	$upper_sd = ($m_index*pow((1+$l_index*$s_index*2),(1/$l_index))-$m_index)/2;

	if (((($bmi-$m_index)/$lower_sd) < -4) || ((($bmi-$m_index)/$upper_sd) > 8) || (($height_inches*2.54) < 20) || (($height_inches*2.54) > 250) || (($patient_weight*0.453592) < 0.5) || (($patient_weight*0.453592) > 400)) {
		$data_error = true;
	} else {
		$bmi_category = get_category_by_percentile($percentile);
	}

}

echo 'Patient status is '.$bmi_category.'.';

/* ////////////////////////////////////////////////////////////////////////////////////////////// */

function get_category_by_bmi($bmi) {
	$results = array(
		'Obese' => 30,
		'Overweight' => 25,
		'Normal' => 18.5,
		'Underweight' => 0
	);
	foreach ($results as $category => $threshold) {
		if ($bmi >= $threshold) {
			return $category;
		}
	}
}

function get_category_by_percentile($percentile) {
	$results = array(
		'Obese' => 95,
		'Overweight' => 85,
		'Normal' => 5,
		'Underweight' => 0
	);
	foreach ($results as $category => $threshold) {
		if ($percentile >= $threshold) {
			return $category;
		}
	}
}

function nearest_value($value, $array) {
	if (array_search($value, $array)) {
    	return $value;
    } else {
		$array[] = $value;
		sort($array);
		$key = array_search($value, $array);
		if ($key == 0) { return $array[$key+1]; }
		if ($key == sizeof($array)-1) { return $array[$key-1]; }
		$dist_to_ceil = $array[$key+1]-$value;
		$dist_to_floor = $array[$key-1]-$value;
		if ($dist_to_ceil <= $dist_to_floor) {
			return $array[$key+1];
		} else {
			return $array[$key-1];
		}
	}
}

function normal_dist($standard_deviation) {
	$p = floatval(0.2316419);
	$b1 = floatval(0.319381530);
	$b2 = floatval(-0.356563782);
	$b3 = floatval(1.781477937);
	$b4 = floatval(-1.821255978);
	$b5 = floatval(1.330274429);
	$t = 1/(1+($p*floatval($standard_deviation)));
	$zx = (1/(sqrt(2*pi()))*(exp(0-pow($standard_deviation,2)/2)));
	$px = 1-floatval($zx)*(($b1*$t)+($b2*pow($t,2))+($b3*pow($t,3))+($b4*pow($t,4))+($b5*pow($t,5)));
	return $px;
}

?>