What is a lipid panel and how is it interpreted?

What is a Lipid Panel and How to Review It

A lipid panel is a blood test that measures total cholesterol, LDL cholesterol (LDL-C), HDL cholesterol (HDL-C), and triglycerides, and should be interpreted by calculating non-HDL cholesterol and assessing these values in the context of the patient's cardiovascular risk factors to guide treatment decisions. 1

Components of a Standard Lipid Panel

A complete lipid profile includes four primary measurements 2, 1:

• Total cholesterol: The sum of all cholesterol in the blood 1
• LDL cholesterol (LDL-C): The primary atherogenic lipoprotein and main treatment target 1, 3
• HDL cholesterol (HDL-C): The "protective" cholesterol inversely associated with cardiovascular disease 1
• Triglycerides: Fat particles that contribute to cardiovascular risk, especially when elevated 1

Non-HDL cholesterol should always be calculated (total cholesterol minus HDL-C) as it captures all atherogenic lipoproteins and serves as a secondary treatment target 1, 3, 4. This calculation is available at no additional cost and is superior to LDL-C alone for predicting cardiovascular events 4.

When to Obtain a Lipid Panel

Fasting vs. Non-Fasting

• Either fasting or non-fasting samples can be used for initial screening in adults 1
• A fasting lipid panel (12 hours without food or drink except water) is preferred for the most accurate assessment, particularly for triglycerides 2
• If non-fasting triglycerides are >500 mg/dL, a fasting panel is required 2
• Non-fasting non-HDL-C >220 mg/dL may indicate genetic hypercholesterolemia requiring further evaluation 2

Screening Recommendations by Age

Adults 40-75 years: Universal screening recommended with lipid panel including all four components 5

Adults 20-39 years: Screen if risk factors present (diabetes, family history of premature CVD, hypertension, smoking, obesity) 5

Adults >75 years: Routine screening can be discontinued unless on statin therapy or with specific cardiovascular risk factors 5

Children and adolescents: Universal screening at ages 9-11 years and 17-21 years; selective screening ages 2-8 years if risk factors present 2, 1, 6

How to Interpret Lipid Values

LDL Cholesterol (Primary Target)

The American College of Cardiology defines LDL-C goals based on cardiovascular risk 1:

• Very high risk (established ASCVD): <70 mg/dL
• High risk (diabetes, multiple risk factors): <100 mg/dL
• Moderate risk: <130 mg/dL
• Low risk: <160 mg/dL

For children and adolescents, the American Heart Association defines 2:

• Acceptable: <110 mg/dL
• Borderline: 110-129 mg/dL
• High: ≥130 mg/dL

HDL Cholesterol

• Low HDL-C is defined as <40 mg/dL and represents an independent cardiovascular risk factor 2
• Higher HDL-C is protective, though the quality of HDL particles matters more than quantity alone 7

Triglycerides

The American Heart Association categorizes triglyceride levels 1:

• Normal: <150 mg/dL
• Borderline high: 150-199 mg/dL
• High: 200-499 mg/dL
• Very high: ≥500 mg/dL (pancreatitis risk)

Non-HDL Cholesterol (Secondary Target)

• Non-HDL-C goals are typically 30 mg/dL higher than LDL-C goals 1
• Particularly useful in patients with elevated triglycerides (150-500 mg/dL) where LDL-C calculation may be less accurate 3, 4

Algorithmic Approach to Review

Step 1: Verify Test Quality

• Confirm fasting status if triglycerides are being used for clinical decisions 2
• If LDL-C <70 mg/dL, consider direct measurement rather than calculated value for accuracy 1

Step 2: Calculate Non-HDL Cholesterol

• Non-HDL-C = Total cholesterol - HDL-C 1, 4
• This should be done for every lipid panel 4

Step 3: Assess Cardiovascular Risk Context

Identify if the patient has 2:

• Clinical ASCVD (prior MI, stroke, angina, revascularization, PAD)
• Diabetes mellitus (considered CHD risk equivalent)
• LDL-C ≥190 mg/dL (likely familial hypercholesterolemia)
• Multiple risk factors requiring 10-year risk calculation

Risk factors to count include 2:

• Age (men ≥45 years, women ≥55 years)
• Family history of premature CHD (male relative <55 years, female relative <65 years)
• Current smoking
• Hypertension
• Low HDL-C (<40 mg/dL)

Note: HDL-C ≥60 mg/dL counts as a "negative" risk factor, subtracting one from the total 2

Step 4: Determine Treatment Intensity

Based on the 2013 ACC/AHA guidelines 2:

High-intensity statin (reduces LDL-C by ≥50%) for:

• Clinical ASCVD age <75 years
• LDL-C ≥190 mg/dL
• Diabetes age 40-75 years with high cardiovascular risk

Moderate-intensity statin (reduces LDL-C by 30-50%) for:

• Diabetes age 40-75 years without additional high-risk features
• 10-year ASCVD risk ≥7.5% (using risk calculator)

Step 5: Monitor Response to Therapy

After initiating statin therapy 2:

• Repeat lipid panel at 4-12 weeks to assess adherence and response
• Expect approximately 50% LDL-C reduction with high-intensity statins
• Expect approximately 30-50% LDL-C reduction with moderate-intensity statins
• Continue monitoring every 3-12 months as clinically indicated

For patients with diabetes, screening at diagnosis and periodically (every 1-2 years) thereafter is reasonable 2, 6

Common Pitfalls and Caveats

Calculation Limitations

• The Friedewald formula (LDL-C = Total cholesterol - HDL-C - [Triglycerides/5]) becomes inaccurate when triglycerides >400 mg/dL 2
• In this situation, direct LDL-C measurement or alternative calculation methods are needed 1

Timing Considerations

• Lipid levels can be transiently affected by acute illness, so avoid testing during acute coronary syndromes or other acute illnesses 2
• Multiple measurements should be averaged before making treatment decisions, particularly in children 2

Special Populations

• Elderly patients (>75 years): The predictive value of cholesterol diminishes; continue monitoring primarily if already on therapy 5
• Children with diabetes: Screen at diagnosis if age ≥2 years, then follow pediatric guidelines 6
• Patients with very high triglycerides (>500 mg/dL): Immediate triglyceride-lowering therapy needed to prevent pancreatitis before focusing on LDL-C 1

Treatment Targets vs. Statin Intensity

• Current guidelines emphasize statin intensity (high vs. moderate) rather than treating to specific LDL-C targets 2
• However, monitoring LDL-C response helps assess adherence and may guide decisions about intensifying therapy 2

Documentation for Clinical Use

• Always document the clinical indication (e.g., "diabetes management," "cardiovascular risk assessment") 6
• Include relevant risk factors in documentation (hypertension, obesity, family history) 6