Lipid Profile Test

Table of Contents

Introduction

A lipid profile test is a routine blood test that measures different types of lipids (fats) in the blood. It is used to assess a person’s risk of developing cardiovascular diseases (CVD) such as heart attack, stroke, and atherosclerosis.
Lipids are essential for various bodily functions, but abnormal levels can lead to the buildup of fat in blood vessels, causing blockage and heart disease.

The test typically includes the measurement of:
1. Total Cholesterol (TC) – the overall amount of cholesterol.
2. High-Density Lipoprotein (HDL-C) – known as “good cholesterol” as it helps remove cholesterol from arteries.
3. Low-Density Lipoprotein (LDL-C) – “bad cholesterol” that deposits fat in blood vessels.
4. Triglycerides (TG) – a type of fat stored in the body and used for energy.
A fasting blood sample (after 9–12 hours without food) is often recommended, especially for accurate triglyceride levels.
The lipid profile helps doctors evaluate the need for lifestyle changes, medications, or further testing. It is also used to monitor patients with conditions like diabetes, obesity or those taking lipid-lowering drugs.

Lipid	Function
Cholesterol	Membrane fluidity, precursor for bile acids, steroid hormones, and vitamin D
Triglycerides	Energy storage, transported in chylomicrons and VLDL
Phospholipids	Components of lipoprotein membranes
Free fatty acids	Energy source, especially during fasting

Lipoprotein	Main Apoproteins	Major Lipid Carried	Density	Function
Chylomicrons	ApoB-48, ApoC-II, ApoE	TG (dietary)	Lowest	Transport dietary TG from intestine to tissues
VLDL	ApoB-100, ApoC, ApoE	TG (hepatic origin)	Very low	Delivers endogenous TG to tissues
IDL	ApoB-100, ApoE	Cholesterol & TG	Intermediate	Transitional lipoprotein between VLDL and LDL
LDL	ApoB-100	Cholesterol	Low	Delivers cholesterol to peripheral tissues
HDL	ApoA-I, ApoA-II	Cholesterol	High	Reverse cholesterol transport to liver

Total Cholesterol (TC):
- Includes cholesterol from all lipoproteins.
- Elevated in both primary and secondary hyperlipidemias.
Triglycerides (TG):
- VLDL carries endogenous TG; chylomicrons carry dietary TG.
- TG > 500 mg/dL may lead to pancreatitis.
High-Density Lipoprotein (HDL-C):
- Protective role; involved in reverse cholesterol transport.
- Low HDL-C is a marker for metabolic syndrome.
Low-Density Lipoprotein (LDL-C):
- Most atherogenic.
- Enters intima → oxidized → taken up by macrophages → foam cell formation → atherosclerosis.
Very-Low-Density Lipoprotein (VLDL-C):
- Estimated as TG/5 (Friedewald); transports endogenous TG.
Non-HDL Cholesterol:
- TC – HDL-C = all atherogenic cholesterol (LDL + VLDL + IDL + Lp(a)).
Atherogenic Index of Plasma (AIP):
- AIP > 0.24 = high CVD risk.

Sample: Serum preferred (EDTA plasma acceptable).
Pre-analytical factors:
- Fasting: 9–12 hrs recommended, especially for TG.
- Avoid alcohol, strenuous exercise, or illness prior to test.
Assays:
- Enzymatic methods for TC, TG, HDL-C.
- Direct methods for HDL-C and LDL-C if TG > 400 mg/dL.
- Calculated LDL using Friedewald:
  - Not valid if TG > 400 mg/dL or in type III hyperlipoproteinemia.

Fredrickson Classification (WHO):
- Type I: ↑ Chylomicrons (rare)
- Type IIa: ↑ LDL (familial hypercholesterolemia)
- Type IIb: ↑ LDL + VLDL (combined hyperlipidemia)
- Type III: ↑ IDL (dysbetalipoproteinemia)
- Type IV: ↑ VLDL (endogenous hypertriglyceridemia)
- Type V: ↑ VLDL + chylomicrons

Condition	Alteration
Diabetes	↑ TG, ↓ HDL, small dense LDL
Hypothyroidism	↑ TC, ↑ LDL
Nephrotic syndrome	↑ TC, ↑ LDL
Liver disease	↓ TC, ↓ HDL (advanced); ↑ TG (fatty liver)
Obesity/Metabolic syndrome	↑ TG, ↓ HDL

Component	Normal Range	Clinical Significance	Implications
Total Cholesterol (TC)	< 200 mg/dL	High levels increase CVD risk; low levels can indicate other health issues.	High (>240 mg/dL): Increased heart disease risk. Low (<160 mg/dL): May indicate health problems.
LDL Cholesterol	< 100 mg/dL	High LDL contributes to plaque buildup, raising CVD risk.	High (>160 mg/dL): Major heart disease risk factor.
HDL Cholesterol	Men: >40 mg/dL, Women: >50 mg/dL	Low HDL increases CVD risk; high HDL is protective.	Low (<40 for men, <50 for women): Increased heart disease risk.
Triglycerides (TG)	< 150 mg/dL	Elevated triglycerides increase CVD risk, especially with low HDL.	High (>200 mg/dL): Increases heart disease and stroke risk.
VLDL Cholesterol	2-30 mg/dL	High VLDL increases CVD risk by contributing to plaque buildup.	High: Contributes to heart disease risk.
Non-HDL Cholesterol	< 130 mg/dL	High non-HDL increases CVD risk.	High (>130 mg/dL): Higher risk for heart disease.

Marker	Clinical Relevance
Apolipoprotein B (ApoB)	Reflects the number of atherogenic particles
Apolipoprotein A1 (ApoA1)	Major protein in HDL
Lp(a)	Genetic, independent CVD risk factor
Small dense LDL	More atherogenic than normal LDL
Oxidized LDL	Involved in foam cell formation

Non-fasting profiles are now acceptable for routine testing.
LDL targets are individualised based on patient risk (e.g., < 70 mg/dL for very high-risk patients).
ESC/EAS 2019 Guidelines recommend using ApoB or non-HDL-C as alternatives to LDL-C in certain conditions.
PCSK9 inhibitors are new agents for LDL lowering.