Glucose metabolism testing is one of the core clinical biochemistry applications for diabetes diagnosis, blood glucose control monitoring, and metabolic syndrome assessment. By quantitatively analyzing blood glucose, glycated hemoglobin, glycated albumin, and other indicators, it provides critical evidence for diabetes screening, diagnosis, classification, and treatment monitoring. The performance of high-quality glucose metabolism testing reagents heavily depends on the proper selection of enzymes, coenzymes, chromogenic substrates, buffers, stabilizers, preservatives, and other raw materials. This article analyzes the core glucose metabolism tests—Glucose (GLU), Glycated Hemoglobin (HbA1c), and Glycated Albumin (GA)—covering their methodologies, key raw materials, and selection criteria.
I. Overview of Glucose Metabolism Testing Projects
Glucose metabolism testing is primarily used for diabetes screening, diagnosis, treatment monitoring, and complication risk assessment.
| Test Item | Clinical Significance | Methodology |
|---|---|---|
| Glucose (GLU) | Diabetes diagnosis, blood glucose control monitoring | GOD-POD method / Hexokinase (HK) method |
| Glycated Hemoglobin (HbA1c) | Long-term blood glucose control assessment (2-3 months) | Immunoturbidimetric method / Boronate affinity chromatography method / HPLC |
| Glycated Albumin (GA) | Medium-term blood glucose control assessment (2-4 weeks) | Enzymatic method (KAO method) |
II. Core Glucose Metabolism Tests and Raw Material Selection
1. Glucose (GLU)
Blood glucose testing is a fundamental test for diabetes diagnosis and blood glucose control monitoring, and is one of the most frequently performed tests in clinical laboratories.
Methodology: Two main methods—GOD-POD method (Glucose Oxidase-Peroxidase method) and HK method (Hexokinase method). The GOD-POD method has lower cost and is the first choice for routine laboratories; the HK method has higher accuracy and is the reference method.
Method 1: GOD-POD Method (Trinder reaction, colorimetric at 500-550 nm)
Reaction Principle:
Glucose + O₂ + H₂O --Glucose Oxidase (GOD)--> Gluconic acid + H₂O₂
H₂O₂ + 4-APP + Phenol (or TOOS) --Peroxidase (POD)--> Colored product (Purple-red/Quinoneimine)
Key Raw Material List (GOD-POD Method):
| Raw Material Name | CAS No. | Function |
|---|---|---|
| Glucose Oxidase (GOD) | 9001-37-0 | Catalyzes glucose oxidation |
| Peroxidase (POD) | 9003-99-0 | Catalyzes color development |
| 4-APP (4-Aminoantipyrine) | 83-07-8 | Chromogenic substrate |
| Phenol | 108-95-2 | Chromogenic substrate (traditional) |
| TOOS | 82692-93-1 | Chromogenic substrate (preferred) |
| Phosphate buffer | — | Maintains pH 6.5-7.5 |
| Good's buffer (PIPES/MOPS/HEPES) | 5625-37-6 / 1132-61-2 / 7365-45-9 | Maintains pH 6.5-7.5 |
Raw Material Selection Points:
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GOD purity: Glucose Oxidase (CAS: 9001-37-0) is the core enzyme. Ensure high activity (≥100 U/mg) and no catalase contamination (which consumes H₂O₂ and leads to low results).
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Chromogenic substrate selection: Traditional use of Phenol (CAS: 108-95-2) is acceptable, but TOOS (CAS: 82692-93-1) is recommended for better water solubility, higher sensitivity, and detection at 550-560 nm.
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Buffer selection: Phosphate buffer is the traditional choice for GOD-POD method, but Good's buffers (PIPES, MOPS, HEPES) offer better compatibility and reduced interference.
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Preservative selection: ProClin 300 (0.02-0.05%) is recommended. Sodium azide is prohibited (inhibits POD).
Method 2: Hexokinase (HK) Method (UV method, monitoring NADPH generation at 340 nm)
Reaction Principle:
Glucose + ATP --Hexokinase (HK)--> Glucose-6-phosphate + ADP
Glucose-6-phosphate + NADP⁺ --G6PDH--> 6-Phosphogluconate + NADPH + H⁺
Glucose concentration is calculated by monitoring the rate of NADPH generation (increase in absorbance at 340 nm).
Key Raw Material List (HK Method):
| Raw Material Name | CAS No. | Function |
|---|---|---|
| Hexokinase (HK) | 9001-51-8 | Catalyzes glucose phosphorylation |
| Glucose-6-Phosphate Dehydrogenase (G6PDH) | 9001-40-5 | Catalyzes G6P dehydrogenation |
| ATP | 56-65-5 | Coenzyme (phosphate donor) |
| NADP⁺ (β-Nicotinamide Adenine Dinucleotide Phosphate, oxidized form) | 53-59-8 | Coenzyme (electron acceptor) |
| Mg²⁺ (Magnesium chloride) | 7791-18-6 | Cofactor |
| Tris buffer | 77-86-1 | Maintains pH 7.5-8.0 |
Comparison of GOD-POD and HK Methods:
| Comparison Item | GOD-POD Method | HK Method |
|---|---|---|
| Advantages | Low cost, simple operation | High accuracy, strong anti-interference capability |
| Disadvantages | Susceptible to uric acid/ascorbic acid interference | Higher reagent cost |
| Suitable Scenarios | Routine clinical laboratories | Reference method, special samples |
| Detection Wavelength | 500-550 nm (colorimetric) | 340 nm (UV) |
| Core Raw Materials | GOD, POD, 4-APP, TOOS | HK, G6PDH, ATP, NADP⁺ |
2. Glycated Hemoglobin (HbA1c)
Glycated hemoglobin is the product of non-enzymatic binding of hemoglobin and glucose, reflecting average blood glucose levels over the past 2-3 months. It is the "gold standard" for long-term diabetes control assessment.
Methodology: Three main methods—Immunoturbidimetric method, Boronate affinity chromatography method, and HPLC. The immunoturbidimetric method is the most common clinical biochemistry method.
Method 1: Immunoturbidimetric Method (Enhanced latex turbidimetry, wavelength 570-600 nm)
Reaction Principle:
Sample HbA1c + Anti-HbA1c antibody-coated latex particles → Immune complex (Turbidity proportional to HbA1c concentration)
Key Raw Material List (Immunoturbidimetric Method):
| Raw Material Name | CAS No. | Function |
|---|---|---|
| Anti-human HbA1c antibody (monoclonal/polyclonal) | — | Specific recognition of HbA1c |
| Latex microspheres (polystyrene) | 9003-53-6 | Signal amplification carrier |
| Hemoglobin capture antibody | — | Captures total hemoglobin |
| PEG (Polyethylene glycol) | 25322-68-3 | Promotes immune complex formation |
| BSA | 9048-46-8 | Blocking agent, stabilizer |
| Phosphate-buffered saline (PBS) | — | Maintains pH 7.0-7.4 |
Raw Material Selection Points:
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Antibody pair is key: HbA1c testing typically uses a double antibody sandwich method, requiring a pair of high-affinity, high-specificity antibodies (anti-HbA1c antibody + hemoglobin capture antibody).
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Latex particle size: 100-300 nm is common for immunoturbidimetry. Larger particle size increases sensitivity.
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Role of PEG: PEG (CAS: 25322-68-3) acts as an enhancer, accelerating immune complex formation and improving detection sensitivity.
Method 2: Boronate Affinity Chromatography Method (Colorimetric, wavelength 600-650 nm)
Reaction Principle:
Sample glycated hemoglobin + Boronate-modified material → Specific binding → Wash to remove unbound material → Color development and measurement
Key Raw Material List (Boronate Affinity Chromatography Method):
| Raw Material Name | CAS No. | Function |
|---|---|---|
| Boronate-modified agarose/polystyrene microspheres | — | Specifically binds glycated hemoglobin |
| Lysis buffer (surfactant) | — | Lyses red blood cells, releases hemoglobin |
| Chromogenic substrate (e.g., TMB) | 54827-17-7 | Color development detection |
Raw Material Selection Points:
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Boronate affinity material: Boronate groups specifically bind to cis-diol structures on glycated hemoglobin, making this the core raw material for this method.
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Microsphere carrier: Both agarose and polystyrene microspheres are suitable, requiring high loading capacity and high specificity.
3. Glycated Albumin (GA)
Glycated albumin is the product of non-enzymatic binding of albumin and glucose, reflecting average blood glucose levels over the past 2-4 weeks. It is more suitable than HbA1c for assessing short-term blood glucose control.
Methodology: Enzymatic method (KAO method, Ketoamine Oxidase method)
Reaction Principle:
Glycated albumin --Protease--> Glycated amino acid fragments
Glycated amino acid fragments + O₂ + H₂O --Ketoamine Oxidase (KAO)--> Amino acids + Glucosone + H₂O₂
H₂O₂ + 4-APP + TOOS --Peroxidase (POD)--> Colored product (Purple-red)
Total albumin concentration is also measured, and the GA/ALB ratio is calculated.
Key Raw Material List:
| Raw Material Name | CAS No. | Function |
|---|---|---|
| Albumin-specific protease | — | Cleaves glycated albumin into glycated amino acid fragments |
| Ketoamine Oxidase (KAO) | — | Catalyzes glycated amino acid oxidation |
| Peroxidase (POD) | 9003-99-0 | Catalyzes color development |
| 4-APP | 83-07-8 | Chromogenic substrate |
| TOOS | 82692-93-1 | Chromogenic substrate |
| Good's buffer (PIPES/MOPS/HEPES) | — | Maintains pH 7.0-8.0 |
| BSA | 9048-46-8 | Stabilizes enzyme activity |
| Albumin detection reagent (BCG method) | — | Measures total albumin concentration |
Raw Material Selection Points:
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Protease specificity: Albumin-specific protease is a key raw material for GA testing. It must cleave only albumin without acting on other serum proteins.
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KAO activity: Ketoamine Oxidase (KAO) activity directly affects detection sensitivity. Ensure high activity (≥10 U/mg).
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Dual-analyte testing: GA testing typically requires simultaneous measurement of glycated albumin and total albumin to calculate the GA/ALB ratio.
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Preservative selection: ProClin 300 (0.02-0.05%) is recommended. Sodium azide is prohibited.
III.Frequently Asked Questions (FAQ)
Q1: What problems occur if GOD activity is insufficient in GOD-POD method glucose tests?
A: GOD (CAS: 9001-37-0) is the core enzyme in the GOD-POD method. Insufficient activity leads to:
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Narrow linear range (low results for high-concentration samples)
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Prolonged reaction time
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Reduced accuracy
Solutions:
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Select high-activity GOD (≥100 U/mg)
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Add stabilizers (BSA, Trehalose) to protect enzyme activity
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Appropriately increase GOD concentration
Q2: How can I eliminate ascorbic acid (Vitamin C) interference in GOD-POD method glucose tests?
A: Ascorbic acid is a major interferent in the GOD-POD method, consuming H₂O₂ and leading to low results.
Solutions:
| Measure | Specific Operation | Raw Materials Involved |
|---|---|---|
| Add Ascorbate Oxidase (ASO) | Add ASO 5-10 kU/L | Ascorbate Oxidase |
| Use high-sensitivity chromogen | Use TOOS instead of Phenol | TOOS (CAS: 82692-93-1) |
| Optimize sample/reagent ratio | Increase reagent volume, decrease sample volume | — |
Q3: How to choose between GOD-POD method and HK method for glucose testing?
A: Both methods have advantages and disadvantages. The choice depends on laboratory requirements.
| Comparison Item | GOD-POD Method | HK Method |
|---|---|---|
| Cost | Low | High |
| Operational complexity | Simple | Moderate |
| Anti-interference capability | Moderate (susceptible to uric acid/ascorbic acid) | Strong |
| Accuracy | Good | Excellent |
| Suitable scenarios | Routine clinical laboratories | Reference method, special samples |
Recommendation: Choose GOD-POD method for routine testing (low cost, simple operation); choose HK method for reference laboratories or special samples (high accuracy).
Q4: What if ATP and NADP⁺ are unstable in HK method glucose tests?
A: ATP (CAS: 56-65-5) and NADP⁺ (CAS: 53-59-8) are heat-sensitive and prone to degradation in liquid reagents.
Solutions:
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Add BSA (0.1-1%) and Trehalose (2-5%) as stabilizers
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Add Mg²⁺ (1-5 mM) as a cofactor, which also stabilizes ATP
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Store reagents at 2-8°C away from light
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Consider lyophilized format to extend shelf life
Q5: How can I improve low sensitivity in HbA1c immunoturbidimetric tests?
A: Low sensitivity is typically related to antibody quality or latex particle size.
Solutions:
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Select high-affinity antibodies (affinity ≥10⁸ L/mol)
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Optimize latex particle size to 200-300 nm (CAS: 9003-53-6)
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Increase PEG concentration to 2-4% (CAS: 25322-68-3)
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Optimize antibody coating process
Q6: What problems occur if protease specificity is insufficient in GA tests?
A: Albumin-specific protease is a key raw material for GA testing. Insufficient specificity leads to:
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Non-specific cleavage of other serum proteins, causing false positives
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Result deviation, inaccurate GA/ALB ratio
Solutions:
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Select high-specificity protease (cleaves only albumin)
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Optimize protease concentration and reaction time
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Use albumin-free control to verify specificity
Q7: Can I use Sodium azide as a preservative for glucose metabolism testing reagents?
A: No. Sodium azide is prohibited in POD-containing reagents.
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Sodium azide (CAS: 26628-22-8) strongly inhibits peroxidase (POD) activity
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Both GOD-POD method and GA method rely on POD for color development
Recommended alternative: ProClin 300 at 0.02-0.05% — broad-spectrum, enzyme-compatible, and safe for Trinder-based assays.
The HK method does not contain POD, but sodium azide is still not recommended (toxic, inhibits other enzymes).
Q8: How can I address narrow linear range in glucose tests?
A: Narrow linear range is typically related to the following factors:
| Possible Cause | Solution |
|---|---|
| Insufficient GOD activity (GOD-POD method) | Increase GOD concentration |
| Insufficient HK/G6PDH activity (HK method) | Increase HK or G6PDH concentration |
| Low chromogenic substrate concentration (GOD-POD method) | Ensure sufficient 4-APP and TOOS |
| Low coenzyme concentration (HK method) | Ensure sufficient ATP and NADP⁺ |
| Incorrect buffer pH | Confirm buffer pH is within recommended range |
| Excessive sample volume | Optimize sample-to-reagent ratio |
IV.Summary
The performance of glucose metabolism testing reagents essentially depends on the proper selection and combination of enzymes, coenzymes, chromogenic substrates, buffers, antibodies, stabilizers, preservatives, and other raw materials. The key points are summarized below:
| Test Item | Core Raw Materials (CAS No.) | Key Considerations |
|---|---|---|
| Glucose (GOD-POD method) | GOD (9001-37-0), POD (9003-99-0), 4-APP (83-07-8), TOOS (82692-93-1) | Add ASO to eliminate ascorbic acid interference |
| Glucose (HK method) | HK (9001-51-8), G6PDH (9001-40-5), ATP (56-65-5), NADP⁺ (53-59-8) | Stabilize ATP and NADP⁺, add Mg²⁺ |
| HbA1c (Immunoturbidimetric) | Anti-HbA1c antibody, Latex microspheres (9003-53-6), PEG (25322-68-3) | Antibody affinity is key |
| HbA1c (Boronate affinity) | Boronate-modified microspheres, TMB (54827-17-7) | Boronate groups specifically bind glycated hemoglobin |
| GA | Albumin-specific protease, KAO, 4-APP, TOOS | Protease specificity is key |
艳 李
