Chemistry: molecular biology and microbiology – Apparatus – Including measuring or testing
Reexamination Certificate
2000-03-31
2002-09-10
Beisner, William H. (Department: 1744)
Chemistry: molecular biology and microbiology
Apparatus
Including measuring or testing
C435S287900, C422S082050, C356S039000, C356S448000
Reexamination Certificate
active
06448067
ABSTRACT:
FIELD OF THE PRESENT INVENTION
The present invention relates to a method and apparatus for determining a chemical component from a sample of matter, in particular for determining the glucose content of blood from a blood sample.
BACKGROUND OF THE PRESENT INVENTION
It is generally known that diabetics are treating themselves in daily life. This is made possible by the use of domestic blood glucose measurement. In the known methods, patients with diabetes place a drop of blood on a test strip, which contains the reagent. The reagent will react with the glucose content of the blood, and generates a well-defined color. The reaction is a multi-stage reaction and is commonly known. The glucose-oxidase enzyme creates hydrogen-peroxide (H
2
O
2
) from the glucose content of the blood, the oxygen of the air and of the water present in the blood. The amount of the H
2
O
2
generated is proportional to the amount of the glucose, and a peroxidase enzyme further activates it. The activated H
2
O
2
oxidizes the indicator (also commonly known) in the test strip, which will change its color. This change of color may be accurately measured.
Earlier test strips have been washed or wiped after the application of the sample, and the color has been determined by comparison with a color chart. More recently, the color has been determined by a small electronic reading device, which calculated automatically the glucose content of the blood sample. The modem test strips are of the so-called no-wipe type, i.e., the blood sample need not be wiped or washed off. With these no-wipe strips the detection of the color reaction is performed on the opposite side to where the sample has been placed. The test strip is provided with a reagent carrier, usually a textile or foil patch, and the test strip is provided with a hole, through which the opposite side of the reagent carrier may be observed. These test strips are almost exclusively analyzed by reading devices, which provide much more objective measurement than the subjective comparison with the color chart. During the reading, the previous devices have measured the reflection of the reagent carrier on a predetermined wavelength. The color generated by the color reaction in the reflection carrier, or more properly on the back side of the carrier, is deduced from the measured reflection value.
The color reaction on such test strips progresses relatively fast, and both at the start of the reaction and after the completion of the reaction, various effects can occur, which affect the results of the color reaction itself. Therefore, in order to determine precisely the result of the color reaction, it is important to perform the reflection measurement serving as the basis of the glucose measurement in a well-defined time interval. Only in this manner is it possible to calibrate properly the relation between the color and the sugar content of the sample.
With the first known devices the measurements were done in the following manner: The patient switched on the device or switched from the stand-by state into the measuring state, after having positioned the sample. This method was not adequate, because the delays until the measurement actually started were varying, due to the switching on, even with by same person. Therefore the need arose to develop such methods, which ensured that the interval between placing the sample on the test strip and the start of the measurements could be determined uniformly, so that the precision of the measurements could improve. Therefore it is desirable to detect automatically, with the measurement device, the start of the color reaction and to detect its shape, so that the device could automatically determine a following time interval when the reflection measurement should be performed. The reflection measurement made in this time interval then could serve as a basis for the determination of the glucose content. Alternatively, in the case of continuous or sampled measurement it is sought to determine when the time T
m
(time point) occurs, so that a single reflection value measured in this time point T
m
could be the basis of the determination of the glucose content. The general object of the present invention is to provide a method for determining this T
m
time point.
When determining this time point, several factors must be considered, which may present contradictory demands. Of course, it is of primary concern that the T
m
time point of the measurement should be determined in a reproducible manner, as well as the R reflection values measured in the T
m
time points so determined. The deduced blood glucose values should also be reproducible, i.e., the accuracy of the blood glucose measurements must not be worse than with known methods.
On the other hand, it is desirable to perform the measurement as quickly as possible, which is, firstly, convenient for the patient, and, secondly, so the battery in the measurement device may last longer. On the other hand, laboratory measurements have shown that the ideal time point for the measurement is dependent on the glucose content of the sample itself. With certain types of test strips it is advantageous to measure earlier the samples with lower glucose content, than those with a higher glucose content. The reason for this is that with some test strips the color reaction takes longer with higher glucose content. Conversely, there are test strips where the opposite is true, that is samples with higher glucose content should be measured earlier, because the color reaction is faster with the higher glucose content and the result is reached earlier. It is advisable to wait longer with low glucose samples until the end of the reaction or close to the end, in order to be able to determine the glucose content precisely. In other words, a good system must be capable of “recognizing”, even before the final measurement, what the interval should be, and the measurement time T
m
can be adjusted accordingly.
This is achieved in newer devices by measuring quasi-continuously the reflection curve, and by determining dynamically the Final measurement time. This latter process contradicts the requirement for simple operations and calculations. This is an important aspect, because the blood glucose measurement devices should be small and portable (i.e., operating from battery), be simple to operate, and, last but not least, be cheap.
A continuous reflection measurement requires the continuous or frequent switching on/off of the light source, typically a LED, and inevitably have a high power consumption. Therefore, it is sought to substitute the continuous measurement with sampling on a frequency as low as possible. It may also be mentioned that a more complicated method requires a more sophisticated controlling processor, which is more expensive. On the other hand, a more complicated algorithm, in a given processor in a given time, allows the evaluation of fewer measurement points, which in turn will result in a less precise measurement. It is less significant, but may be taken into consideration that the power consumption of the processor is higher with more calculating steps. This latter factor may play a role if the controlling algorithm of the device is not made by digital processor but by analog circuits, e.g. due to considerations of reliability. With higher power consumption the device will operate for a shorter time, so indirectly its reliability will worsen (i.e. the probability of malfunction due to the run-down of the batteries will increase).
The document U.S. Pat. No. 4,199,261 (Tidd et al.) discloses an optical reflection meter, which is used to determine the glucose content in urine of diabetics. The device is capable of determining if the sample carrier is dry or wet, by comparing the measured reflection with a predetermined threshold value. The value measured on the dry sample carrier is used for calibrating the device. Following this, the user inserts the sample carrier, which has been wetted with the urine sample, in the device, which is automatically identified by the device. After th
77 Elektronika Muszeripari KFT
Beisner William H.
McDonnell & Boehnen Hulbert & Berghoff
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