THE EFFECT OF ASCORBIC ACID ON GLUCOSE URINE ASSAY BY COPPER SULPHATE REDUCING SYSTEM AND HEXOKINASE METHOD.
A.H. Shah, A.M. Ali, N.M. Al-Jaser and I.A. Al-Omer
Directorate General for Laboratories and Blood Banks, King Saud Medical City, Ministry of Health, P.O.Box 59082, Riyadh-11525, Saudi Arabia.
Keywords: Urinalysis, Glucose monitoring, Strip tests, Ascorbic acid interference, Copper reduction test, Hexokinase method.
Background: The objective of the present study was to compare the results obtained by different methods used in glucose monitoring. Diabetic patients are known to use urine glucose strips or dipsticks tests or glucose pads for urine analysis. Blood glucose monitoring instruments such as different types of blood gluco-meters and digital blood glucose monitoring devices are also available in the local market for home glucose testing.
Methodology: Some of those tests are officially used in the laboratories of different hospitals, where routine analysis is mainly done on advanced Chemical Analyzers.
Results: Some discrepancies were observed in the results of glucose monitoring by different methods. A serious interference was recorded by ascorbic acid in reagent-strip reactions for assay of urinary glucose and hemoglobin. The test methods are known to be based on different chemical reactions including enzymatic and color reactions.
Conclusion: Mostly, the urine concentration of ascorbic acid, uric acid, mercury, copper and iron were labeled to be the main cause of interference. In the present study 2991 urine samples having detectable ascorbic acid levels (?10 mg/dL) were tested by different methods and the results were compared with standard Dimension Chemical Analyzer (Dimension Dade Behring). Ascorbic acid in various concentrations was found to cause serious interference in glucose monitoring, however, hexokinase method was found more reliable.
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