Diagnostic Features of Dyslipidemia
The diagnostic features of dyslipidemia include abnormal lipid profile measurements, specifically elevated total cholesterol, elevated LDL cholesterol, elevated triglycerides, reduced HDL cholesterol, and the presence of small dense LDL particles, with specific cutoff values defining different risk categories. 1
Primary Lipid Parameters for Diagnosis
Essential Lipid Profile Components
- Total cholesterol (TC): Measures all cholesterol in blood
- LDL cholesterol (LDL-C): Primary target for therapy and risk assessment
- HDL cholesterol (HDL-C): Protective factor when elevated
- Triglycerides (TG): Important marker for metabolic abnormalities
- Non-HDL cholesterol: Total cholesterol minus HDL cholesterol; represents all atherogenic lipoproteins 1
Calculation Methods
LDL cholesterol calculation (Friedewald formula):
- In mmol/L: LDL-C = TC – HDL-C – (0.45 × TG)
- In mg/dL: LDL-C = TC – HDL-C – (0.2 × TG)
- Note: Valid only when TG <4.5 mmol/L (400 mg/dL) 1
Non-HDL cholesterol calculation:
- Non-HDL-C = TC – HDL-C
- Advantage: Can be calculated in non-fasting state 1
Diagnostic Cutoff Values
Adult Risk Categories
| Risk Level | LDL-C | HDL-C | Triglycerides |
|---|---|---|---|
| High | ≥130 mg/dL | <40 mg/dL | ≥400 mg/dL |
| Borderline | 100-129 mg/dL | 40-59 mg/dL | 150-399 mg/dL |
| Low | <100 mg/dL | ≥60 mg/dL | <150 mg/dL |
Note: For women, HDL-C values should be increased by 10 mg/dL 2
Specific Dyslipidemia Patterns
Common Dyslipidemia Patterns
- Hypercholesterolemia: Elevated LDL-C as primary abnormality
- Hypertriglyceridemia: Elevated triglycerides as primary abnormality
- Combined hyperlipidemia: Elevations in both LDL-C and triglycerides
- Low HDL cholesterol: Reduced HDL-C as primary abnormality 3
Atherogenic Dyslipidemia Triad
The most common pattern in type 2 diabetes and metabolic syndrome:
- Elevated triglycerides (>150 mg/dL)
- Decreased HDL cholesterol (<40 mg/dL in men, <50 mg/dL in women)
- Increased small, dense LDL particles (qualitative change) 1, 4
Special Diagnostic Considerations
When Standard Calculations Are Not Valid
- When triglycerides ≥400 mg/dL, the Friedewald formula becomes inaccurate
- In these cases, direct LDL-C measurement or ultracentrifugation is required 3
- Non-HDL cholesterol remains valid even with high triglycerides 1
Secondary Dyslipidemia Assessment
Laboratory tests to exclude secondary causes:
- Urinalysis
- Plasma creatinine
- Thyroid-stimulating hormone (TSH)
- Fasting glucose
- Protein electrophoresis
- Liver function tests (alkaline phosphatase and transaminases) 3
Familial Hypercholesterolemia Screening
- Suspect in adults with LDL-C >5 mmol/L (>190 mg/dL)
- Suspect in children with LDL-C >4 mmol/L (>150 mg/dL)
- Especially with family history of premature CVD or tendon xanthomas 2
Advanced Diagnostic Tests
When to Consider Advanced Testing
- Lipoprotein electrophoresis: Useful for diagnosing Type III dyslipidemia (broad beta band) and detecting chylomicrons
- Apolipoprotein B-100: Useful in young subjects with coronary artery disease but normal LDL-C
- Lipoprotein lipase activity or apolipoprotein C-II levels: Helpful in children and young adults with severe hypertriglyceridemia 3
Pitfalls and Caveats
- Fasting state is important for accurate triglyceride measurement but not necessary for cholesterol measurements 2
- LDL particle size measurement is not routinely recommended in clinical practice despite its potential relevance 1
- Secondary causes of dyslipidemia (diabetes, obesity, hypothyroidism, renal disease, liver disease, medications) must be ruled out before diagnosing primary dyslipidemia 1
- Non-HDL cholesterol may be a better predictor of cardiovascular risk than LDL-C alone, especially in patients with metabolic syndrome or diabetes 2
By systematically evaluating these diagnostic features, clinicians can accurately identify dyslipidemia patterns and guide appropriate treatment decisions to reduce cardiovascular risk.