What are the diagnostic criteria for hyperlipidemia?

Diagnostic Criteria for Hyperlipidemia

Hyperlipidemia is diagnosed based on fasting serum lipid levels, with specific cutoff values defining different types and severities of lipid disorders. The diagnosis requires assessment of total cholesterol, LDL-C, HDL-C, and triglycerides 1.

LDL Cholesterol Criteria

LDL-C is the primary lipid parameter used for screening, risk estimation, diagnosis, and management of hyperlipidemia 2. The following classifications apply:

• Borderline high: 130-159 mg/dL (3.4-4.1 mmol/L)
• High: 160-189 mg/dL (4.1-4.9 mmol/L)
• Very high: ≥190 mg/dL (≥4.9 mmol/L) 1

Triglyceride Criteria

The Endocrine Society defines hypertriglyceridemia using these cutoffs 2:

• Mild: 150-199 mg/dL (1.7-2.3 mmol/L)
• Moderate: 200-999 mg/dL (2.3-11.3 mmol/L)
• Severe: 1,000-1,999 mg/dL (11.3-22.6 mmol/L)
• Very severe: ≥2,000 mg/dL (≥22.6 mmol/L)

HDL Cholesterol Criteria

Low HDL-C is defined as:

• <40 mg/dL (<1.0 mmol/L) for men
• <50 mg/dL (<1.3 mmol/L) for women 1

Non-HDL Cholesterol

Non-HDL-C (total cholesterol minus HDL-C) should be calculated, especially when triglycerides are elevated. Elevated non-HDL-C is defined as ≥130 mg/dL in patients with triglycerides ≥200 mg/dL 1, 3.

Laboratory Considerations

• Fasting samples (12 hours) are preferred for initial diagnosis, particularly for accurate triglyceride assessment 1
• LDL-C calculation using the Friedewald formula is valid only when triglycerides are <4.5 mmol/L (400 mg/dL); direct LDL-C measurement is required for patients with higher triglyceride levels 1
• Re-testing is recommended to confirm abnormal values before making a definitive diagnosis 1

Familial Hypercholesterolemia Criteria

Familial hypercholesterolemia should be suspected in patients with:

• LDL-C ≥5 mmol/L (190 mg/dL) in adults or ≥4 mmol/L (150 mg/dL) in children
• Premature CHD (before age 55 in men, 60 in women)
• Family history of premature CVD
• Presence of tendon xanthomas 2, 1

Secondary Causes Assessment

Before diagnosing primary hyperlipidemia, evaluate for secondary causes 2, 1:

• Metabolic conditions: Diabetes mellitus, hypothyroidism, obesity
• Lifestyle factors: Excessive alcohol intake, physical inactivity
• Medical conditions: Renal disease, liver disease, pregnancy
• Medications: Thiazide diuretics, beta-blockers, estrogen, corticosteroids, antiretroviral protease inhibitors, antipsychotics

Clinical Implications

• Mild or moderate hypertriglyceridemia may increase cardiovascular disease risk
• Severe and very severe hypertriglyceridemia (>1,000 mg/dL) significantly increase the risk of pancreatitis 2
• Elevated LDL-C is causally important in atherosclerosis 4
• Combined elevations of multiple lipid parameters (mixed dyslipidemia) significantly increase cardiovascular risk 3

Common Pitfalls in Diagnosis

• Failure to obtain properly fasting samples for initial diagnosis
• Relying solely on total cholesterol without measuring LDL-C, HDL-C, and triglycerides
• Not accounting for medication effects on lipid levels
• Overlooking secondary causes of hyperlipidemia
• Missing familial disorders by not evaluating family members when appropriate 1

By following these diagnostic criteria and considering both primary and secondary causes, clinicians can accurately diagnose hyperlipidemia and initiate appropriate management to reduce cardiovascular risk and prevent complications.