Blood glucose measurement is used to determine the glucose content of the blood and is an easy-to-measure value for the diagnosis and monitoring of diseases that are associated with a changed blood glucose level, especially for the control of diabetes mellitus. The absolute glucose value is determined from the blood, and the HbA1c value and urine sugar are also measured for monitoring the course of the disease.
According to the guidelines of the German Diabetes Society (DDG) of 2012, fasting blood glucose in healthy persons should be below 100 mg/dl, between 100 and 110 mg/dl one speaks of a disturbed glucose tolerance, which is regarded as a suspected diabetes and must be checked annually, above a value of 110 mg/dl DDG sees the manifestation of diabetes mellitus. If the blood sugar level is not measured fasting, the so-called “casual” plasma glucose level, the value should normally be below 200 mg/dl. At the doctor’s, blood sugar is usually measured by taking blood from a venous vessel and evaluating it in the laboratory.
The blood sugar level is determined from the blood plasma, which is particularly important for making a diagnosis of diabetes mellitus. For monitoring the progress of the disease, however, and especially for self-monitoring at home, there are portable blood glucose meters that obtain the blood sugar value from whole blood or capillary blood, preferably from the fingertip. Although this method is much faster and simpler, it is also less accurate than the measurement by blood sampling due to numerous disturbing factors.
1.) Various methods have become established in the field of portable blood glucose meters, for example photometric, which was standard in the first devices for domestic use, as well as amperometric measurement. Both measurements are enzyme-catalyzed in the devices.
2.) In the photometric measurement, after applying the drop of blood, a reaction of the sugar present in the blood with the chemical substances on the test strip takes place, whereupon the meter measures the blood sugar by the characteristic light absorption of the test strip after the chemical reaction. The degree of absorption depends on the glucose concentration.
3.) In the amperometric measuring method, a drop of capillary blood is also applied to the test strip. The test field contains the enzyme glucose oxidase, with which the blood sugar reacts.
This chemical reaction establishes contact between some electrodes, so that after applying an electrical voltage from the device, the blood glucose concentration can be calculated by measuring the time course of the current intensity. The HbA1c value is another way to determine the blood glucose value from the blood. This refers to hemoglobin molecules of the erythrocytes to which a glucose molecule has been non-enzymatically bound.
The number of these modified molecules correlates with the level of blood sugar, even if it is not possible to obtain an exact and absolute blood sugar value from it. Since the sugar molecule remains bound for the entire life of the red blood cell, this value allows conclusions to be drawn about the course of the blood sugar level in the last 6-8 weeks and is therefore relevant for the long-term monitoring of the drug settings of diabetics. It should be checked once per quarter in diabetics.
The HbA1c value should normally be between 4 and 6.2 percent. In the meantime, several new ideas for blood glucose monitoring have been developed, which aim at a procedure without blood sampling. These methods are currently still in the trial phase.
For example, a possibility has been discovered to determine the blood sugar through the skin using a laser device that can measure the concentration-dependent light absorption of the blood glucose. Furthermore, there are approaches to determine the blood sugar in the tear fluid. In the case of very high glucose concentrations in the blood, the concentration can also exceed the so-called kidney threshold, which leads to the occurrence of glucose in the urine.
Due to the fact that the renal threshold can easily be influenced by numerous interfering factors, this value is not very meaningful, however, and nowadays other standardised methods of measurement are more commonly used. In exceptional cases, however, it can be used for monitoring the progress of non-insulin-dependent diabetics. Notes on self-measurement with portable blood glucose meters: To avoid falsification of the measured values, make sure that the hands are clean and dry.
Damp hands, even after disinfection with alcohol, could dilute the blood drop. Furthermore, fingers should not be cold, as this can make it difficult to obtain blood. In addition, as little pressure as possible should be applied to extract the drop of blood from the finger, as otherwise liquid can leak from the tissue and possibly falsify the measurement. In order to reduce the puncture pain, care should be taken to puncture at the side of the fingertip and not directly into the fingertip, as the pain receptors are not as tightly located there.