Process for stabilizing the content of glycated protein of a...

Chemistry: natural resins or derivatives; peptides or proteins; – Peptides of 3 to 100 amino acid residues – Peptides containing saccharide radicals – e.g. – bleomycins – etc.

Reexamination Certificate

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C530S350000

Reexamination Certificate

active

06552165

ABSTRACT:

BACKGROUND OF INVENTION
The invention concerns a process for stabilizing the content of glycated protein of a sample on a matrix material and an appropriately treated matrix material for this. In addition the invention concerns an element for collecting, transporting and storing sample material to be analysed containing an absorptive matrix material and a system containing such an element and a sealable covering in which the element can be transported.
The glycation of haemoglobin and serum proteins is increased in patients with diabetes mellitus. The increase is dependent on the glucose concentration and the incubation period of protein with glucose. In these cases the serum proteins, including haemoglobin, are not glycated enzymatically but rather by means of an uncatalysed chemical reaction of glucose with amino groups of proteins. Experts assume that the concentration of a particular protein-glucose adduct reflects the glucose concentration over a particular period as well as the turn-over rate of the protein. Glycated haemoglobin is regarded as an indicator of the average blood glucose concentration during the last two to three months before the blood collection and examination. Glycated serum protein shows the blood glucose concentration during a shorter period of time. The determination of glycated protein such as glycated haemoglobin (HbA
1c
) or glycated serum protein is therefore considerably important for the long-term glycemic control of diabetes patients.
In order to examine blood for the content of glycated protein the sample must often be transported to a far distant laboratory. The content of glycated protein in the sample should not change during this transport period and during a possible subsequent waiting period. The examination of blood samples which had been stored for a long period for glycated haemoglobin is reported in Clinical Chemistry 29, 1080-1082 (1983). This shows that whole blood can be stored up to 21 days at room temperature with essentially no change in the HbA
1c
content.
However, the transport of liquid blood samples is complicated and involves risks such as breakage of the transport vessel. In addition the puncture of a vein is necessary to collect whole blood although the amounts obtained by withdrawing capillary blood from the finger pad would be sufficient for the analysis. Thus methods have been developed for the transport and analysis of smaller amounts of blood in which capillary blood is applied to filter paper and allowed to dry there. The filter paper is subsequently transported to the site of the examination. Here a disk containing the sample is cut out from the filter paper, eluted and the eluate is examined. The report in Clinical Chemistry 28, 386-387 (1982) refers to such a method. In this report it is stated that the content of glycated protein changes considerably compared to the original sample during blood sample storage on filter paper. After storage of whole blood on filter paper considerably increased measured values for glycated protein are found.
The impregnation of filter paper with glucose oxidase to prevent the increase in the content of glycated haemoglobin caused by storage of blood on filter paper is described in Clinical Chemistry 32, 869-871 (1986). However, impregnation with glucose oxidase was not able to completely prevent the increase of glycated protein. The false increase in the values can only be reduced by this measure. A further disadvantage of impregnating with glucose oxidase is its own instability during storage under the usual storage conditions. Similar conclusions are reached by an article in Diabetes Care 10, 352-355 (1987). Here it is reported that the treatment of filter paper with glucose oxidase or with ethanol cannot satisfactorily prevent a false increase in the values for glycated haemoglobin when blood is stored on filter paper.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention was therefore to stabilize the content of glycated protein in a sample when stored on a matrix material. After storage of the glycated protein on a matrix material a value should be found for the glycated protein which corresponds to that found after sample collection and before storage.
This object is achieved by the subject matter characterized in more detail in the patent claims.
BRIEF DESCRIPTION OF THE DRAWING
The invention concerns a process for stabilizing the content of glycated protein of a sample on a matrix material by impregnating the matrix material with a boric acid buffer with a pH greater than or equal to 10.5. A comparable stabilization is also possible when the matrix material carries a transition metal salt.
The invention in addition concerns the matrix material for taking up the sample material which is to be examined for its content of glycated protein which is characterized in that it is impregnated with boric acid buffer with a pH larger than or equal to 10.5 or it carries a transition metal salt.
An additional subject matter of the invention is an element for collecting, transporting and storing sample material to be analysed containing an absorptive matrix material wherein the element is characterized in that the matrix material is impregnated with boric acid buffer with a pH larger than or equal to 10.5 or it carries a transition metal salt.
Finally a subject matter of the invention is a system containing an element characterized as above and a sealable covering in which the element can be transported which is characterized in that the element is such as has already been characterized above as being according to the invention.
Within the scope of the present invention matrix materials denote absorptive materials which are capable of absorbing a liquid containing glycated protein. Glycated protein, i.e. protein carrying sugar residues, is mainly located in the blood but also in sample materials derived from blood such as serum or plasma and moreover also in other body fluids such as urine or saliva. Materials which can absorb such sample materials are preferably fibres but can also be in principle non-fibrous. Preferred fibrous absorptive matrix materials are fleeces, fabrics or knitted fabrics. Fleeces are quite especially preferred. The fibrous matrix materials can contain glass, cellulose, polyester fibres and also viscose and polyvinyl alcohol. Fleece materials containing meltable copolyester fibres in addition to glass fibres, polyester fibres, polyamide fibres, cellulose fibres or cellulose derivative fibres as described in the European Patent Application 0 571 941 can also be used advantageously as the matrix material. Non-fibrous materials can for example be membranes.
According to the invention it has turned out that sample material containing glycated protein that is located on a matrix material can be stored very well without any essential change in the content of glycated protein if the matrix material is impregnated with boric acid buffer with a pH of greater than or equal to 10.5 or if the matrix material carries a transition metal salt. In this case the concentration of the boric acid buffer is of secondary importance. Particularly good results are obtained if the boric acid buffer has a pH value of more than or equal to 11. Suitable buffer concentrations are in the range between 300 and 1000 mmol/l, which corresponds to about 18.6-62 g/100 ml.
Transition metal salts have a similarly good stabilizing action such as nickel or copper salts. Nickel salts are particularly preferred. Water-soluble transition metal salts are preferably used according to the invention. Corresponding chlorides are for example well suited. In order to be active according to the invention transition metal salt concentrations on the matrix material of more than 5 g/m
2
and particularly preferably of more than 10 g/m
2
have proven to be suitable according to the invention.
Sample material containing glycated protein such as for example glycated haemoglobin which has been applied to a matrix material as described above has resulted in values for glycated protein that are comp

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