Raw Material Selection Points:

• Selective surfactant is the core technology: This is the key raw material for the HDL-C direct method. Its function is to selectively protect HDL particles while disrupting LDL, VLDL, and chylomicrons so they do not participate in the reaction. Formulations vary by manufacturer, typically involving non-ionic surfactants with specific HLB values or polyanion blends.

• Surfactant selection: Common options include Dextran sulfate (CAS: 9011-18-1), Phosphotungstate-Mg²⁺ complexes, and PEG-modified surfactants.

• Enzymes and chromogens: Same as TC testing—CEH, CHOD, POD, and 4-APP + TOOS.

4. Low-Density Lipoprotein Cholesterol (LDL-C)

LDL-C is known as "bad cholesterol" and is a core risk factor for atherosclerosis.

Methodology: Direct method (selective surfactant, colorimetric at 500-550 nm)

Reaction Principle:

Selective surfactant → Selectively solubilizes/releases LDL-C while protecting HDL and other lipoproteins
LDL-C + Enzyme reagent (CEH + CHOD + POD + chromogen) → Color development (proportional to LDL-C concentration)

Key Raw Material List:

Raw Material Selection Points:

• Selective surfactant is the core technology: In contrast to HDL-C, LDL-C testing requires a surfactant that selectively solubilizes/releases LDL-C while protecting HDL, VLDL, and chylomicrons from reacting.

5. Apolipoprotein A1 (ApoA1) and Apolipoprotein B (ApoB)

Apolipoprotein A1 is the major apolipoprotein of HDL. Apolipoprotein B is the major apolipoprotein of LDL and VLDL. Both are used for cardiovascular disease risk assessment and are more specific than HDL-C/LDL-C.

Methodology: Immunoturbidimetric method (enhanced latex turbidimetry, wavelength 570-600 nm)

Reaction Principle:

Sample ApoA1/ApoB + Anti-ApoA1/ApoB antibody-coated latex particles → Immune complex (Turbidity proportional to concentration)

Key Raw Material List:

Raw Material Selection Points:

• Antibody quality is key: Anti-ApoA1 and anti-ApoB antibodies are core raw materials, requiring high affinity, high specificity, and good batch-to-batch consistency.

• Latex particle size: 100-300 nm is common for immunoturbidimetry. Larger particle size increases sensitivity but may increase non-specific reactions.

• Role of PEG: PEG (CAS: 25322-68-3) acts as an enhancer, accelerating immune complex formation and improving detection sensitivity.

III.Frequently Asked Questions (FAQ)

Q1: Which chromogenic substrate should I choose for TC and TG tests?

A: The 4-APP (CAS: 83-07-8) + TOOS (CAS: 82692-93-1) combination is recommended.

TOOS allows detection at a higher wavelength, reducing serum background interference and providing higher sensitivity.

Q2: Can I use Tris buffer for TC and TG tests?

A: No. Use Good's buffers (PIPES, MOPS, or HEPES).

• Tris reacts with chromogenic substrates (4-APP, TOOS), producing colored byproducts that increase reagent blank.

• Phosphate buffers may cause precipitation, especially in the presence of Mg²⁺.

Recommendation: PIPES (CAS: 5625-37-6) pH 6.5-7.0, MOPS (CAS: 1132-61-2) pH 6.8-7.5, HEPES (CAS: 7365-45-9) pH 7.0-7.5.

Q3: What is the core technology for HDL-C and LDL-C direct methods?

A: The core technology is selective surfactants.

Formulations vary by manufacturer. Optimization based on specific methodology is required.

Q4: What problems occur if LPL activity is insufficient in TG tests?

A: LPL (CAS: 9004-02-8) is the most critical enzyme in TG testing. Insufficient activity leads to:

• Narrow linear range (low results for high-concentration samples)

• Prolonged reaction time

• Reduced accuracy

Solutions:

• Select high-activity LPL (≥10 U/mg)

• Add stabilizers (BSA, Trehalose) to protect enzyme activity

• Appropriately increase LPL concentration

Q5: How can I prevent lipid component oxidation in lipid testing reagents?

A: Lipid components (especially cholesterol esters and triglycerides) are prone to oxidation, leading to reagent deterioration.

Solutions:

• Add antioxidant: BHT (CAS: 128-37-0) 0.01-0.05%

• Add chelating agent: EDTA·2Na (CAS: 6381-92-6) 1-2 mM

• Store away from light at 2-8°C

• Use brown bottles for packaging

Q6: How can I improve low sensitivity in ApoA1/ApoB tests?

A: Low sensitivity is typically related to antibody quality or latex particle size.

Solutions:

• Select high-affinity antibodies (affinity ≥10⁸ L/mol)

• Optimize latex particle size to 200-300 nm (CAS: 9003-53-6)

• Increase PEG concentration to 2-4% (CAS: 25322-68-3)

• Optimize antibody coating process

Q7: Can I use Sodium azide as a preservative for lipid testing reagents?

A: No. Sodium azide is prohibited.

• Sodium azide (CAS: 26628-22-8) strongly inhibits peroxidase (POD) activity

• POD is a key enzyme in all Trinder reactions (TC, TG, HDL-C, LDL-C)

Recommended alternative: ProClin 300 at 0.02-0.05% — broad-spectrum, enzyme-compatible, and safe for Trinder-based assays.

Q8: How can I address narrow linear range in TC and TG tests?

A: Narrow linear range is typically related to the following factors: