What is the Low-Density Lipoprotein (LDL) to High-Density Lipoprotein (HDL) ratio?

What is the LDL/HDL Ratio?

The LDL/HDL ratio is a cardiovascular risk marker calculated by dividing LDL cholesterol by HDL cholesterol, with higher ratios indicating greater coronary heart disease risk. 1

Definition and Calculation

The LDL/HDL cholesterol ratio combines measurements of "bad" cholesterol (LDL) with "good" cholesterol (HDL) to provide a single risk assessment value 1. This ratio makes intuitive sense as it combines an atherogenic lipoprotein variable (LDL) with a protective one (HDL) 1.

Clinical Significance for Risk Assessment

The LDL/HDL ratio is superior to measuring either LDL or total cholesterol alone for predicting coronary heart disease risk. 2

Risk Stratification Thresholds

• In men: An LDL/HDL ratio >5.0 combined with triglycerides >2.3 mmol/L (>203 mg/dL) identifies a high-risk subgroup with 3.8 times greater risk of cardiac events 3
• In women: The total cholesterol/HDL ratio (which parallels LDL/HDL) provides better risk discrimination than LDL alone, with ratios ranging from <3 (low risk) to ≥9 (high risk) 2
• The Helsinki Heart Study demonstrated that patients with LDL/HDL ratio >5 were at substantially elevated risk, particularly when combined with elevated triglycerides 3

Advantages Over Individual Lipid Measurements

The ratio captures the complex interaction between LDL and HDL better than either measurement alone. 4

• The benefits of increasing HDL are strongest among persons with high LDL, and conversely, the benefits of decreasing LDL are greatest among those with low HDL 4
• The LDL/HDL ratio was the best single predictor of cardiac events in the Helsinki Heart Study placebo group 3
• Risk stratification based on this ratio is more efficient than relying primarily on LDL cholesterol levels alone 2

Important Clinical Caveats

Not a Treatment Target

While the LDL/HDL ratio is valuable for risk assessment, it is not established as a treatment goal. 1

• European guidelines acknowledge that low HDL cholesterol may rival high LDL cholesterol as a risk factor for coronary heart disease, but there is insufficient evidence to use HDL as a therapeutic target 1
• The ratio should be used as a marker of increased risk rather than necessarily as an index of treatment success 1

Interpretation Requires Context

• The ratio must be interpreted as part of a complete lipid profile, not in isolation 5
• Even with a favorable ratio, elevated absolute LDL cholesterol levels still warrant appropriate management according to risk category 5
• Consider other cardiovascular risk factors including hypertension, diabetes, smoking, and family history 5

Relationship to Other Lipid Markers

The total cholesterol/HDL ratio is often used interchangeably with LDL/HDL ratio in clinical practice 1. However, in patients with elevated triglycerides, the total cholesterol/HDL ratio may better capture metabolic abnormalities associated with insulin resistance syndrome than the LDL/HDL ratio alone 6.

Alternative: Apolipoprotein B/A1 Ratio

The apolipoprotein B (apo B) to apolipoprotein A1 (apo A1) ratio represents a protein-based alternative to cholesterol ratios 1. While this ratio is "beyond doubt one of the strongest risk markers," it is not yet generally recommended due to limited availability, higher cost, and lack of additional information over standard lipid measurements 1.

Practical Application

Current treatment guidelines focus on absolute LDL cholesterol targets based on overall cardiovascular risk category rather than ratio targets 1:

• Very high risk (CHD or equivalent): LDL <100 mg/dL (2.6 mmol/L) 1
• High risk: LDL <130 mg/dL (3.35 mmol/L) 1
• Moderate risk: LDL <160 mg/dL (4.15 mmol/L) 1

The LDL/HDL ratio serves as an adjunctive tool for refining risk assessment, particularly in intermediate-risk patients where traditional algorithms perform less well 1.