Bioquímica Clínica 02/02

Summary

This lesson focuses on the analysis of blood glucose levels, explaining key tests such as fasting glucose, glucose tolerance (OGTT), and hemoglobin A1c. It covers methodologies like glucose oxidase and hexokinase, emphasizing their roles in diagnosing and monitoring diabetes. The importance of fasting, proper sample collection, and the impact of conditions like anemia or hemoglobinopathies on results is discussed. The session highlights how these tests reveal both current glucose levels and long-term control, with a focus on ensuring accurate results through appropriate lab practices and understanding various diagnostic tools.

Takeaways

• 😀 Fasting is crucial for accurate blood glucose measurement, with the ideal fasting time being 8-10 hours, not exceeding 16 hours.
• 😀 The use of sodium fluoride (NaF) in blood collection tubes helps prevent glycolysis, ensuring accurate glucose readings by inhibiting glucose breakdown.
• 😀 Glucose concentration in the blood can be measured using enzymatic reactions, with the glucose oxidase method being the most common and reliable for this purpose.
• 😀 The glucose tolerance test (OGTT) involves fasting, ingesting 75g of glucose, and then measuring glucose levels after 2 hours to assess the body’s ability to process glucose.
• 😀 Hemoglobin A1c (HbA1c) reflects average blood glucose levels over the past 2-3 months, providing insight into long-term glucose control and diabetes management.
• 😀 Anemia and hemoglobinopathies can distort HbA1c results due to a lower concentration of red blood cells or altered hemoglobin structure, which affects glucose binding.
• 😀 The HbA1c test uses various methods, with High-Performance Liquid Chromatography (HPLC) being considered the gold standard for determining glucose levels in hemoglobin.
• 😀 The ideal pre-analytical phase requires careful handling of blood samples to avoid inaccuracies, such as using EDTA tubes for HbA1c or fluoride tubes for glucose tests.
• 😀 In cases of abnormal blood glucose readings, a proper understanding of test timing, fasting, and patient history (e.g., anemia or medication use) is essential for accurate diagnosis.
• 😀 The glucose tolerance test can also help detect impaired glucose tolerance (IGT), which may indicate the early stages of diabetes or risk for diabetes development.
• 😀 For accurate glucose measurement, the choice of method (e.g., glucose oxidase vs. exokinase) depends on factors like the required precision and type of test being conducted.

Q & A

What is the primary purpose of the fasting glucose test (Glicemia de jejum)?

The primary purpose of the fasting glucose test is to measure the concentration of glucose in the blood after an 8 to 10-hour fasting period. This ensures a balanced, homeostatic state and provides an accurate reading of blood glucose levels.

Why is it important to fast for 8 to 10 hours before a fasting glucose test?

Fasting for 8 to 10 hours is essential to ensure that the blood glucose levels are not influenced by recent food intake. If the fasting period is shorter or longer than recommended, it may result in inaccurate test results.

What role does sodium fluoride play in blood glucose testing?

Sodium fluoride is used as an inhibitor of glycolysis during the pre-analytical phase of blood glucose testing. It helps preserve glucose in the blood sample by preventing its breakdown through the glycolytic pathway.

What are the differences between plasma and serum in glucose testing?

Plasma is obtained when a blood sample is collected in tubes containing sodium fluoride, which inhibits glycolysis. Serum, on the other hand, is collected without any preservative and requires quick analysis (within one hour) to avoid erroneous results.

What is the most commonly used method for measuring glucose in blood samples in Brazil?

The most commonly used method for measuring blood glucose in Brazil is the glucose oxidase method. This method uses glucose oxidase to oxidize glucose and produce a color change, which is then measured spectrophotometrically.

How does the glucose oxidase method work?

In the glucose oxidase method, glucose in the sample reacts with oxygen and water in the presence of glucose oxidase, forming glucuronic acid and hydrogen peroxide. The hydrogen peroxide then reacts with a chromogen to produce a color change, which is measured to determine glucose concentration.

What is the oral glucose tolerance test (OGTT) and how is it performed?

The oral glucose tolerance test (OGTT) is performed after fasting glucose is measured. The individual then consumes a 75g glucose solution, and their glucose levels are measured again after two hours. This test helps diagnose diabetes and evaluate glucose tolerance.

What is the significance of the HbA1c test in monitoring glucose levels?

The HbA1c test measures the percentage of hemoglobin that is irreversibly bound to glucose. It provides a long-term average of blood glucose levels over the past 2-3 months, making it an important marker for diagnosing and monitoring diabetes.

Why might a patient with anemia receive inaccurate HbA1c test results?

A patient with anemia may have fewer red blood cells, which means less hemoglobin available for glycation. As a result, the HbA1c test may underestimate the actual level of glycation and lead to inaccurate results.

What is the relationship between HbA1c and average blood glucose levels?

There is a direct correlation between HbA1c levels and average blood glucose concentrations. For example, a blood glucose level of 140 mg/dL typically correlates with an HbA1c level of around 6.5%. This helps provide insight into the patient’s glucose control over the past few months.