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Glucose Measurement in Serum and Plasma: A Comprehensive Overview
Introduction to Glucose Measurement Methods
Glucose measurement is a critical diagnostic tool for managing diabetes mellitus and other metabolic disorders. Various methods have been developed to measure glucose levels in serum and plasma, each with its own advantages and limitations. This article synthesizes the findings from multiple research studies to provide a clear understanding of the methodologies and their implications.
Automated Methods for Glucose Determination
Hexokinase-Glucose-6-Phosphate Dehydrogenase Method
One efficient method for determining glucose levels in serum or plasma involves the hexokinase/glucose-6-phosphate dehydrogenase reaction. This automated method is noted for its specificity to glucose and is unaffected by high concentrations of endogenous substances or common drugs that interfere with other glucose measurement techniques.
Potentiometric Reaction-Rate Method
Another innovative approach is the automatic potentiometric reaction-rate method, which uses a new filtering technique to remove precipitated proteins. This method allows for the rapid and accurate measurement of glucose in small sample volumes, with relative errors within 2% and an average measurement time of about 30 seconds.
Ferricyanide-Phosphomolybdate Reaction
The ferricyanide-phosphomolybdate reaction, modified for use with the AutoAnalyzer, is another precise and sensitive method for determining glucose in serum and plasma. This method has been adapted to improve the flow system and reagents, ensuring reliable results.
Comparison of Serum and Plasma Glucose Levels
Stability and Accuracy
The stability of glucose in serum and plasma samples is a significant concern, especially when there is a delay in sample processing. Studies have shown that plasma glucose levels are generally about 11% higher than those in whole blood when the hematocrit is normal. Additionally, plasma samples tend to be more stable than serum samples, with less degradation over time .
Influence of Sample Handling
The method of blood processing can significantly influence glucose levels. For instance, immediate centrifugation and rapid measurement of plasma samples can prevent glycolysis and provide more accurate glucose readings. In contrast, serum samples require a clotting period before centrifugation, which can lead to glucose degradation if not processed promptly .
Practical Implications
In clinical practice, plasma is often preferred over serum for glucose measurement due to its stability and the ability to process samples quickly without waiting for clotting. However, some studies suggest that serum can be used interchangeably with plasma within the first hour if stored at 2-4 degrees Celsius, without significant alterations in glucose concentration.
Conclusion
The determination of glucose levels in serum and plasma is a vital diagnostic procedure with various methods available to ensure accuracy and efficiency. Automated methods like the hexokinase-glucose-6-phosphate dehydrogenase reaction and the potentiometric reaction-rate method offer reliable results. While plasma is generally preferred for its stability, serum can also be used effectively under specific conditions. Understanding the nuances of these methods and the factors influencing glucose stability can help clinicians make informed decisions in managing diabetes and other metabolic disorders.
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