Introduction
Clinical chemistry testing is one of the oldest, most fundamental, and most mature branches of the in vitro diagnostics (IVD) field. By quantitatively analyzing metabolites, enzymes, and other substances in blood, urine, and other body fluids, it provides critical evidence for assessing the function of organs such as the liver, kidneys, and heart, as well as for diagnosing metabolic diseases such as diabetes and dyslipidemia. From automated analyzers in tertiary hospitals to semi-automated analyzers in primary healthcare facilities, clinical chemistry testing accounts for the largest daily workload in clinical laboratories. The performance of high-quality clinical chemistry testing reagents heavily depends on the proper selection and combination of substrates, enzymes, coenzymes, chromogenic substrates, buffers, stabilizers, preservatives, detergents, and other raw materials. As the general outline for the clinical chemistry testing raw material series, this article systematically introduces the core position of clinical chemistry testing in IVD, the classification of major tests, core technical principles, a panorama of core raw materials, and general principles for raw material selection, laying the foundation for subsequent in-depth analyses by test category.
I. Core Position of Clinical Chemistry Testing in IVD
1.1 Market Position of Clinical Chemistry Testing
Clinical chemistry testing is one of the largest and most fundamental segments of the IVD market. According to industry data, clinical chemistry testing accounts for approximately 20-25% of the global IVD market, and its testing volume accounts for the highest proportion (approximately 50-60%) in clinical laboratories. Its main drivers include:
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Rigid demand for routine physical examinations: Liver function, renal function, lipids, and blood glucose are core items in physical examination panels
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Growing demand for chronic disease management: Chronic diseases such as diabetes, hypertension, and dyslipidemia require regular monitoring
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Technological maturity and cost advantages: High automation, low unit testing cost, and reliable results
1.2 Major Tests Covered by Clinical Chemistry Testing
| Test Category | Specific Tests | Primary Clinical Significance |
|---|---|---|
| Liver Function | ALT, AST, ALP, GGT, TBIL, DBIL, TP, ALB | Hepatocellular injury, biliary obstruction, hepatic synthetic function |
| Renal Function | UREA, CREA, UA, Cys-C | Glomerular filtration function, tubular function |
| Lipids | TC, TG, HDL-C, LDL-C, ApoA1, ApoB | Cardiovascular disease risk assessment |
| Blood Glucose | GLU, HbA1c, GA | Diabetes diagnosis, blood glucose control monitoring |
1.3 Irreplaceability of Clinical Chemistry Testing in IVD
Compared with other IVD technologies, clinical chemistry testing has the following irreplaceable advantages:
| Comparison Item | Clinical Chemistry Testing | Immunoassay | Molecular Diagnostics |
|---|---|---|---|
| Target | Metabolites, electrolytes, enzymes | Proteins, hormones, antibodies | Nucleic acids (DNA/RNA) |
| Sensitivity | Medium-high (μM-nM) | High (fM-pM) | Extremely high (single copy) |
| Testing Time | 5-30 minutes | 15 minutes-2 hours | 1-4 hours |
| Unit Cost | Low | Medium-high | High |
| Automation Level | Fully automated | Medium-high | Medium-high |
| Application Scenarios | Routine checkups, chronic disease monitoring | Infectious diseases, oncology, hormones | Pathogen detection, genotyping |
Core Conclusion: Clinical chemistry testing has an irreplaceable position in routine testing of metabolites and enzyme activities, and its low cost, high throughput, and speed make it the foundation platform of clinical laboratories.
II. Core Technical Principles of Clinical Chemistry Testing
The methodology system of clinical chemistry testing is primarily based on two principles: Enzymatic reaction-colorimetric method and Enzymatic reaction-UV method.
2.1 Enzymatic Reaction-Colorimetric Method (Trinder Reaction)
This is the most commonly used method in clinical chemistry testing, applicable to TC, TG, GLU, UA, CREA, and other tests.
Principle:Target substance + Enzyme → H₂O₂
H₂O₂ + 4-APP + Chromogenic substrate (TOOS/Phenol) --POD--> Colored product (Purple-red/Quinoneimine)
Detection Wavelength: 500-550 nm
Applicable Tests: TC, TG, GLU (GOD-POD method), UA, CREA (enzymatic method)
Key Raw Materials: Target detection enzymes (CHOD, GOD, uricase, etc.), peroxidase (POD), 4-APP, TOOS/phenol, Good's buffers
2.2 Enzymatic Reaction-UV Method (Continuous Monitoring Method)
Applicable to ALT, AST, UREA, and other tests that use NADH or NADPH as coenzymes.
Principle:Target substance + NAD(P)H --Enzyme--> Product + NAD(P)⁺
Monitor the decrease (or increase) in absorbance at 340 nm due to NAD(P)H consumption/generation
Detection Wavelength: 340 nm
Applicable Tests: ALT, AST, UREA
Key Raw Materials: Substrates (L-alanine, L-aspartic acid, α-ketoglutaric acid), NADH, tool enzymes (LDH, MDH, urease, GLDH), Tris buffer
2.3 Comparison of Technical Principles
| Comparison Item | Trinder Reaction (Colorimetric) | UV Method (Continuous Monitoring) |
|---|---|---|
| Signal Generation | H₂O₂ + Chromogen → Colored product | NAD(P)H consumption/generation |
| Detection Wavelength | 500-550 nm | 340 nm |
| Representative Methods | GOD-POD (glucose), CHOD-PAP (cholesterol) | IFCC method (ALT/AST) |
| Preferred Buffer | Good's buffers (PIPES/MOPS/HEPES) | Tris buffer |
| ⚠️ Key Warning | Avoid Tris buffer | Avoid sodium azide |
III. Panorama of Core Raw Materials for Clinical Chemistry Testing
The performance of clinical chemistry testing reagents essentially depends on the proper selection and combination of the following five major categories of raw materials. Each category plays an irreplaceable role in the reagent system: Core substrates and enzymes are the "engine" of the detection reaction, coenzymes and substrates are the "fuel" that transmits signals, chromogenic substrates are the "color developers" that produce visual signals, buffers are the "stabilizers" that maintain the reaction environment, stabilizers and protectants are the "protective layers" that extend reagent shelf life, preservatives are the "gatekeepers" that prevent microbial contamination, and detergents/surfactants are the "lubricants" that optimize reaction conditions.
3.1 Core Substrates and Enzymes — The "Engine" of the Detection Reaction
Functional Explanation: Enzymes are the core catalysts in clinical chemistry testing. They specifically recognize target substances and convert them into detectable signals. Without enzymes, the detection reaction cannot proceed. Substrates are the "raw materials" on which enzymes act, being converted into products upon enzymatic catalysis. Different tests require different enzyme combinations. The quality (activity, purity, stability) of enzymes directly determines the sensitivity, linear range, and accuracy of the test reagent.
Selection Points:
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Higher enzyme activity means lower required, reducing reagent cost
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Higher enzyme purity means fewer non-specific reactions and more accurate test results
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Batch-to-batch activity consistency directly affects reagent inter-batch variability
3.2 Coenzymes — The "Fuel" That Transmits Signals
Functional Explanation: Coenzymes are not enzymes themselves, but they are essential "helpers" in enzyme-catalyzed reactions, responsible for transferring electrons or chemical groups during the reaction. NADH and NADPH have characteristic absorption peaks at 340 nm; when they are oxidized to NAD⁺ or NADP⁺, the absorbance decreases—a property used in UV method detection. ATP is the "carrier" of phosphate groups, providing energy for phosphorylation reactions. Substrates are the "raw materials" on which enzymes act; their purity and concentration directly affect reaction rate and linear range.
Selection Points:
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NADH is light-sensitive and prone to oxidative degradation; store away from light and add stabilizers
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ATP and NADP⁺ are heat-sensitive; add protectants in liquid reagents
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Coenzyme purity ≥98% is a basic requirement for ensuring detection sensitivity
3.3 Chromogenic Substrates — The "Color Developers" That Produce Visual Signals
Functional Explanation: Chromogenic substrates are colorless themselves, but under the catalysis of peroxidase (POD), they react with H₂O₂ to produce colored products (typically purple-red or quinoneimine compounds). By measuring the absorbance of the colored product (500-550 nm), the concentration of the target substance can be indirectly calculated. 4-APP is the standard chromogen for the Trinder reaction, paired with different coupling chromogens (e.g., phenol, TOOS) to form different color development systems.
Selection Points:
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TOOS has a higher detection wavelength (550-560 nm), effectively reducing serum background interference
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TOOS has good water solubility and does not easily precipitate in reagents
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Insufficient purity of chromogenic substrates leads to elevated reagent blank
3.4 Buffers — The "Stabilizers" That Maintain the Reaction Environment
Functional Explanation: The core function of buffers is to maintain the stability of the reaction system's pH. Enzyme catalytic activity is extremely sensitive to pH—deviation from the optimal pH leads to decreased enzyme activity or even inactivation. For example, ALP has the highest activity in DEA buffer (pH 9.8), but is strongly inhibited in Tris buffer. Furthermore, buffer components can also affect the behavior of other components in the reaction system: Tris reacts with chromogenic substrates in the Trinder reaction and therefore cannot be used for TC, TG, GLU, and other tests.
Selection Points:
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The buffer's pKa should be close to the required working pH to provide maximum buffering capacity
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Good's buffers have low metal ion binding and low UV absorption, making them ideal for Trinder reactions
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DEA not only buffers but also activates ALP; it is the standard buffer system recommended by the IFCC
3.5 Stabilizers and Protectants — The "Protective Layers" That Extend Reagent Shelf Life
Functional Explanation: Clinical chemistry testing reagents are typically liquid formulations and face various degradation risks during storage and use: enzyme proteins may denature and lose activity, NADH may be oxidized, lipid components may be oxidized, and metal ions may catalyze degradation reactions. Stabilizers "protect" these sensitive components, extending reagent shelf life. BSA stabilizes enzyme activity by providing an inert protein environment; trehalose and glycerol protect protein structure; EDTA chelates heavy metal ions that catalyze degradation; glutathione acts as a reducing agent to protect NADH; BHT prevents oxidation of lipid components.
Selection Points:
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NADH is sensitive to light, oxygen, and metal ions; must use a combination of glutathione + EDTA + light-protective packaging
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Lipid components in lipid reagents are prone to oxidation; BHT must be added
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For liquid enzyme reagents, it is recommended to add BSA (0.1-0.5%) and trehalose (2-5%)
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For lyophilized reagents, it is recommended to increase trehalose concentration (5-10%) as a bulking agent
Through the detailed analysis of the seven major raw material categories above, it can be seen that the performance of clinical chemistry testing reagents is the result of the synergistic action of multiple raw materials. Core substrates and enzymes determine "whether detection is possible," coenzymes and substrates determine "the chemical pathway of detection," chromogenic substrates determine "how to see the results," buffers determine "whether the reaction environment is appropriate," stabilizers and protectants determine "how long the reagent lasts," preservatives determine "whether the reagent is contaminated," and detergents determine "whether the reaction is smooth." Inappropriate selection of raw materials at any step can lead to decreased reagent performance or even failure. Therefore, raw material selection and optimization are the core tasks of clinical chemistry testing reagent development.
IV. General Principles for Raw Material Selection in Clinical Chemistry Testing
4.1 Buffer Selection Principles
| Principle | Explanation | Example |
|---|---|---|
| Match the detection method | Good's buffers for Trinder reaction; Tris for UV method | Use PIPES for CREA test |
| Avoid side reactions | Tris reacts with chromogenic substrates | Avoid Tris for TC test |
| Maintain optimal pH | pH directly affects enzyme activity and reaction rate | ALP test pH 9.8 (DEA) |
4.2 Stabilizer Usage Principles
| Principle | Explanation | Recommendation |
|---|---|---|
| Protect easily degraded components | NADH is sensitive to light/oxygen | Add glutathione and EDTA; protect from light |
| Protect enzyme activity | Enzymes are easily inactivated in liquids | Add BSA and trehalose |
| Prevent lipid oxidation | Cholesterol esters and triglycerides are easily oxidized | Add BHT and EDTA |
4.3 Preservative Selection Principles
| Principle | Explanation | Recommendation |
|---|---|---|
| Enzyme compatibility | Sodium azide inhibits many enzymes | Use ProClin 300 |
| No interference with detection | Sodium azide absorbs UV, interfering with 340 nm detection | Use ProClin 300 |
| Broad-spectrum antimicrobial | Inhibits bacteria and fungi | ProClin 300 (broad-spectrum) |
VII. Summary
Clinical chemistry testing is the most fundamental and widely applicable technology segment in the IVD field, accounting for approximately 20-25% of the IVD market, with the highest testing volume in clinical laboratories. It is based on enzymatic reaction-colorimetric methods and enzymatic reaction-UV methods as its core technologies, covering the four major test categories of liver function, renal function, lipids, and blood glucose.
The performance of clinical chemistry testing reagents essentially depends on the proper selection and combination of the following five major categories of raw materials:
| Raw Material Category | Core Points |
|---|---|
| Core substrates and enzymes | High activity, high purity, batch consistency |
| Coenzymes and substrates | NADH/NADP⁺ purity ≥98%, require stabilization |
| Chromogenic substrates | 4-APP + TOOS combination is optimal |
| Buffers | Good's buffers for Trinder reaction; Tris for UV method; DEA for ALP |
| Preservatives | ProClin 300 (preferred) |
Core Warnings:
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⚠️ POD-containing Trinder reaction reagents (TC, TG, GLU, UA, CREA) must NOT use sodium azide
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⚠️ Trinder reaction and ALP test must NOT use Tris buffer
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⚠️ NADH must be stored away from light; glutathione and EDTA are recommended
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