Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving blood clotting factor
Patent
1991-10-16
1999-02-02
Gitomer, Ralph
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving blood clotting factor
435 14, 435 26, C12Q 154
Patent
active
058663495
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for quantitatively determining total glucose content in whole blood, and to a disposable cuvette and a photometer for carrying out the method.
Determination of whole blood glucose is made for diagnosing and controlling diabetes, and also in endocrinological investigations. In uncertain cases of unconciousness, too, determination of whole blood glucose may be justified. Diabetes is one of the world's major health problems, and it is estimated that more than 40 million people suffer from this disease and that the prevalence of type II diabetes seems to increase.
Several methods for determining glucose are known. Many old methods have today been abandoned because of unspecificity or the involvement of carcinogenic reagents.
By glucose in blood, whole blood glucose, is meant non-protein-bound glucose present in the blood. Glucose is freely distributed in the extracellular water and also in the intracellular water, e.g. in the red blood cells, but not necessarily in the same concentration. This means that the total content of glucose in whole blood differs from the total content of glucose in plasma or serum. The diagnostic criteria for e.g. diabetes are predominantly based on whole blood glucose. To the clinician, it is therefore clearly advantageous to have the glucose determinations made directly on whole blood. The difference between determinations of glucose in whole blood and glucose in plasma or serum is discussed by W. T. Caraway: Amer. J. Clin. Path. 37:445, 1962. Many glucose tests currently used, where intact red blood cells are removed, incorrectly state their results as blood glucose and may therefore cause confusion in medical diagnosis because of the different references used.
Most of today's specific glucose determination methods are based on reagents containing enzymes or enzyme systems. Three different enzyme systems are predominant, viz. glucose oxidase, hexokinase and glucose dehydrogenase (GDH).
The present invention preferably relies on reagents containing glucose dehydrogenase (GDH). Previously known determination methods using GDH are described in U.S. Pat. No. 4,120,755 and U.S. Pat. No. 3,964,974. These prior art determination methods using GDH are traditional wet-chemical methods.
None of the above-mentioned methods is however suitable for determining glucose in undiluted whole blood. Although Example 7 in U.S. Pat. No. 3,964,974 describes a whole blood glucose method, this method is based on dilution and protein precipitation or separate hemolysis of the blood sample.
EP 84112835.8 describes a whole blood glucose method for undiluted blood. The chemical enzyme reaction used is based on glucose oxidase, and an optical reflectance measurement is carried out at a wavelength above 600 nm. It is well known that hemoglobin interferes with oxidase reactions. Also, oxidase reactions require access to free oxygen. Therefore, using a microcuvette for performing a whole blood glucose determination with the glucose oxidase system in undiluted blood involves substantial problems.
From U.S. Pat. No. 4,088,448 is previously known a microcuvette which can be used for hemoglobin measurement (Hb measurement) of blood. The cuvette is pretreated with a reagent, such that when a blood sample is drawn into the cuvette, the walls of the red blood cells are dissolved and a chemical reaction is initiated, the result of which allows Hb determination by absorption measurement directly through the cuvette which, to this end, has an accurately defined gap width.
The method according to U.S. Pat. No. 4,088,448 for Hb determination on glucose is not easily applied in practice since an absorption measurement for determining the glucose content is strongly interfered with by the absorption caused by the hemoglobin. Variations in the hemoglobin concentration will therefore interfere with the glucose determination to a considerable extent.
Thus, present-day methods are complicated. They often require dilution of the blood sample or only perform a glucose determination on the b
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Lilja Jan Evert
Nilsson Sven-Erik Lennart
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