Note: The Friedewald formula is less accurate when Triglycerides are above 400 mg/dL.
Understanding the Calculated LDL Blood Test
LDL (Low-Density Lipoprotein) is often referred to as "bad" cholesterol because high levels can lead to a buildup of plaque in your arteries, increasing the risk of heart disease and stroke. While some laboratories measure LDL directly, most use the Friedewald Formula to calculate it based on other components of your lipid panel.
How the Friedewald Formula Works
The standard calculation used by this tool and most medical labs is:
LDL = Total Cholesterol – HDL – (Triglycerides / 5)
This formula assumes that the ratio of triglycerides to cholesterol in Very Low-Density Lipoprotein (VLDL) is relatively constant at 5:1. However, this assumption breaks down if triglyceride levels are excessively high (over 400 mg/dL), in which case a direct LDL measurement is required.
Interpreting Your LDL Results
According to the Adult Treatment Panel (ATP III) guidelines, LDL levels for adults are categorized as follows:
LDL Level (mg/dL)
Category
Below 100
Optimal
100 – 129
Near Optimal / Above Optimal
130 – 159
Borderline High
160 – 189
High
190 or above
Very High
Realistic Example of LDL Calculation
Suppose a patient receives their blood test results with the following numbers:
Total Cholesterol: 220 mg/dL
HDL Cholesterol: 45 mg/dL
Triglycerides: 160 mg/dL
Step 1: Divide Triglycerides by 5 (160 / 5 = 32).
Step 2: Subtract HDL and the result from Step 1 from Total Cholesterol (220 – 45 – 32).
Result: LDL = 143 mg/dL. This would be categorized as Borderline High.
When is a Calculated LDL Not Accurate?
There are specific scenarios where the calculation might provide misleading results:
High Triglycerides: If triglycerides are over 400 mg/dL, the formula is unreliable.
Non-Fasting Tests: Triglyceride levels fluctuate significantly after meals, which affects the calculated LDL. Most doctors recommend a 9-12 hour fast before a lipid panel.
Type III Dysbetalipoproteinemia: This rare genetic condition alters the VLDL composition, making the 5:1 ratio invalid.
function calculateLDL() {
var total = parseFloat(document.getElementById('totalChol').value);
var hdl = parseFloat(document.getElementById('hdlChol').value);
var trig = parseFloat(document.getElementById('trigly').value);
var resultBox = document.getElementById('ldlResultBox');
var valueDisplay = document.getElementById('ldlValueDisplay');
var categoryDisplay = document.getElementById('ldlCategoryDisplay');
var trigWarning = document.getElementById('trigWarning');
if (isNaN(total) || isNaN(hdl) || isNaN(trig)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (hdl >= total) {
alert("HDL cannot be greater than or equal to Total Cholesterol.");
return;
}
// Friedewald Formula: LDL = TC – HDL – (TG / 5)
var ldlValue = total – hdl – (trig / 5);
// Display result box
resultBox.style.display = 'block';
// Check if result is logically possible
if (ldlValue < 0) {
valueDisplay.innerHTML = "Result: N/A";
categoryDisplay.innerHTML = "Check input values; calculation resulted in a negative number.";
categoryDisplay.style.color = "#c0392b";
trigWarning.style.display = 'none';
return;
}
valueDisplay.innerHTML = "Calculated LDL: " + Math.round(ldlValue) + " mg/dL";
// Categorization Logic
var category = "";
var color = "";
if (ldlValue = 100 && ldlValue = 130 && ldlValue = 160 && ldlValue 400) {
trigWarning.style.display = 'block';
} else {
trigWarning.style.display = 'none';
}
}