LOW-DENSITY LIPOPROTEIN (LDL) CHOLESTEROL
LDL cholesterol (LDL-C) is commonly known as the “bad cholesterol.” It plays a key role in assessing cardiovascular risk and is calculated from other lipid profile components.
1. Purpose
The estimation of LDL cholesterol in human serum is performed by calculation using a standard formula. Measuring serum LDL cholesterol helps in:
- Screening lipid status to detect atherosclerotic risks
- Monitoring response to lipid-lowering measures
- Diagnosis and classification of hyperlipidemias
A strong relationship exists between serum LDL cholesterol and the risk of coronary heart disease.
LDL > 130 mg/dL is considered a risk factor for coronary and cerebrovascular disease and is also useful for lipoprotein phenotyping.
2. Principle
The LDL cholesterol concentration is determined by calculation rather than direct chemical assay. It uses the **Friedewald Formula**, which estimates LDL cholesterol from total cholesterol, triglycerides, and HDL levels.
3. Procedure / Calculation
The LDL cholesterol (mg/dL) is calculated as:
LDL = Total Cholesterol − (Triglycerides / 5 + HDL)
⚠️ Valid only when triglyceride level is below 400 mg/dL.
4. Reference Range
| Classification | LDL Cholesterol (mg/dL) |
|---|---|
| Desirable | < 130 |
| Borderline elevation | 130 – 159 |
| High / Elevated | > 160 |
Calculation valid up to triglyceride levels of 400 mg/dL.
5. Clinical Interpretation
- Optimal LDL (< 100 mg/dL): Minimal atherosclerotic risk
- Borderline (130–159 mg/dL): Moderate risk — lifestyle modification advised
- High (> 160 mg/dL): Significant cardiovascular risk — medical intervention recommended
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