Total Cholesterol

Table of Contents

Introduction

Cholesterol is a waxy, fat-like substance that plays a crucial role in the body.
It is a key structural component of cell membranes, a precursor for synthesizing steroid hormones (like estrogen and testosterone), vitamin D, and bile acids, aiding fat digestion.
While cholesterol is essential for physiological functions, its excess in the blood is a significant risk factor for cardiovascular diseases, including atherosclerosis, myocardial infarction, and stroke.
Total cholesterol refers to the sum of all cholesterol carried in various lipoproteins, including low-density lipoproteins (LDL), high-density lipoproteins (HDL), and very low-density lipoproteins (VLDL).
Measuring total cholesterol provides insights into lipid metabolism and overall cardiovascular risk.
One of the classical methods for determining total cholesterol is Zak’s Method, which relies on chemical reactions to produce a measurable colored compound.
The measurement of total cholesterol is a cornerstone in lipid profile testing, which is crucial for diagnosing and monitoring conditions like hyperlipidemia, metabolic syndrome, and other cardiovascular risk factors.

Principle Zak’s Method

Proteins in serum are precipitated by ferric chloride. The cholesterol present in the protein-free filtrate is oxidized and dehydrated with ferric chloride, acetic acid, and sulphuric acid to a red-colored compound. A measure of the color’s intensity indicates the cholesterol concentration in the serum.

Reagents

05 g ferric chloride hexahydrate in acetic acid,
H2SO4.
Standard cholesterol solution: (5 ml ≡ 0.2 mg cholesterol), prepared fresh in ferric chloride—acetic acid reagent from stock cholesterol solution (100 mg/100 ml acetic acid).

Sample

Serum or plasma (collected after 12–14 hours of fasting for accurate results).
Preparation of PFF (Protein filtrate) from serum. Take 9.9 ml ferric chloride—acetic acid reagent in a dry test tube and 0.1 ml serum (Dilution of blood ≡ 1in 100). Mix by inversion using paraffin film, keep for 5 minutes, centrifuge, and use clear supernatant as PFF.

Procedure

	T	S	B
PFF	5 ml	–	–
Standard cholesterol solution	–	5 ml	–
Ferric chloride-acetic acid reagent	–	–	5 ml
Conc. H₂SO₄	3 ml	3 ml	3 ml

Calculation

The concentration of total cholesterol in the sample is calculated using the formula:

Cholesterol concentration (mg/dL) = Sample Absorbance/Standard Absorbance×Standard Concentration (mg/dl

Normal Values

The normal range of total cholesterol depends on age, sex, and other factors. General reference ranges are:

Desirable: < 200 mg/dL (5.2 mmol/L)
Borderline High: 200–239 mg/dL (5.2–6.2 mmol/L)
High: ≥ 240 mg/dL (6.2 mmol/L)

Age-Specific Reference Ranges:

Children: 120–170 mg/dL
Adults: 140–200 mg/dL
Elderly (>65 years): Up to 220 mg/dL may be normal.

Clinical Significance

Elevated Total Cholesterol

High cholesterol levels (hypercholesterolemia) are a key risk factor for cardiovascular diseases. Causes include:

Primary hyperlipidemia (genetic):
- Familial hypercholesterolemia.
- Familial combined hyperlipidemia.
Secondary hyperlipidemia (acquired):
- A diet high in saturated fats and cholesterol.
- Hypothyroidism.
- Diabetes mellitus.
- Nephrotic syndrome.
- Obstructive liver disease.
- Chronic kidney disease.

Clinical Implications:

Atherosclerosis: Plaque buildup in arteries leading to reduced blood flow.
Coronary artery disease: Increased risk of heart attacks.
Stroke: Higher chances of ischemic stroke due to arterial blockages.

Decreased Total Cholesterol

Low cholesterol levels (hypocholesterolemia) are less common but may indicate:

Malnutrition or malabsorption.
Hyperthyroidism.
Liver diseases (e.g., cirrhosis or liver failure).
Chronic infections or inflammation.
Severe anemia.