How to correctly compare with venous blood!

Case 1: A diabetic patient bought a blood glucose meter and was worried about its accuracy. So, one day on an empty stomach, he took his own blood glucose meter to compare with the hospital's blood glucose meter.

Result: The blood glucose measured by his own blood glucose meter was 6.6mmol/L, and the blood glucose meter measured by the hospital was 5.4mmol/L. He believed that the two blood glucose meters had an error of about 1.2. In the future, when you measure your blood sugar yourself, subtract 1.2 from the value.

Case 2: A patient measured his blood sugar at home and his blood sugar was 4.8mmol/L 2 hours after a meal. However, the patient did not feel hungry, so he thought his blood glucose meter was inaccurate. So, he went to the hospital laboratory the next day to draw venous blood and measure his blood sugar. Then, while drawing blood, he also measured his blood sugar with a blood glucose meter (using fingertip blood).

Result: Both blood sugar values were 7.2mmol/L. He felt that the blood glucose meter was too accurate and felt relieved.

Are these two methods correct? How to use your own blood glucose meter to compare it with the hospital's laboratory biochemical method in a standardized way?

How hospitals compare the accuracy of blood glucose meters

First, let’s look at a national standard and a clinical guideline. The national standard is the Ministry of Health’s WS/T 226-2002 "Guidelines for Blood Glucose Measurement with Portable Blood Glucometers", which stipulates two comparison plans:

Plan 1: Venous blood sample comparison test (This plan is currently adopted by some hospitals. The blood glucose meters used in various clinical departments are compared with the laboratory biochemical methods of the hospital twice a year. Venous whole blood samples are used. The specific method is slightly).

Plan 2: Capillary blood and venous blood comparison test. In the fasting state, first take the whole blood from the fingertips, use a blood glucose meter to test according to the manufacturer's instructions, then immediately draw venous blood, anticoagulate, and use a laboratory analyzer to complete the plasma glucose test within 30 minutes.

Blood samples with blood glucose concentrations in the range of 2.8mmol/L to 22.2mmol/L should be obtained from original venous blood samples. In addition, extreme blood samples of ≤2.8mmol/L and ≤22.2mmol/L can be prepared separately by the laboratory.

Now that there is a standardized comparison method, how to judge the results? This requires comparing with another clinical guideline, the "Clinical Application Guidelines for Blood Glucose Monitoring in China" issued by the Diabetes Branch of the Chinese Medical Association, 2015, to determine whether the test results of the blood glucose meter are accurate. The annual guide requirements are as follows:

If the test range of blood glucose is lower than 5.6mmol/L, its allowable error is ±0.83mmol/L;

If it is ≥5.6mmol/, its allowable error is ≤±15%.

Therefore, the comparison between the blood sugar value of biochemical test and fingerstick blood test value is based on this range. If it exceeds this range, it will be inaccurate.

Why are there two comparison ranges?

For the sake of safety, there will be two criteria: lower than 5.6mmol/L and higher than 5.6mmol/L.

If it is lower than 5.6 mmol/L, there is a risk of hypoglycemia, so the blood glucose meter is required to be more accurate, and ±0.83mmol/L is more stringent.

To give a specific example, if the blood sugar test range is lower than 5.6mmol/L:

If the blood sugar measured by your blood glucose meter is 5.4 mmol/L, and the venous blood drawn in the biochemical laboratory is 5.1 mmol/L, taking the 5.1 mmol/L in the biochemical laboratory as the standard, plus 0.83 mmol/L, it is 5.93 mmol/L, and 5.4 is within the range of 5.93, so congratulations, your meter is accurate in the median range.

On the contrary, if the blood sugar measured by your blood glucose meter is 4.1mmol/L, the venous blood drawn in the biochemical laboratory is still 5.1mmol/L, subtracting 0.83mmol/L is 4.27mmol/L, and 4.1 is lower than the range of 4.27, so Sorry, the median value of your blood glucose meter is not accurate!

If it is ≥5.6mmol/, its allowable error is ±15%:

If the blood sugar measured by your blood glucose meter is 15.4 mmol/L, and the venous blood drawn in the biochemical laboratory is 17.2 mmol/L, taking the 17.2 in the biochemical laboratory as the standard and adding 15.4×15% is: 2.31+15.4=17.71 mmol/L , and 17.2 is within the range of 17.71, so congratulations, your blood glucose meter is accurate within the high value range!

On the contrary, if the blood sugar measured by the blood glucose meter is 15.8mmol/L, the venous blood drawn in the biochemical laboratory is still 17.2mmol/L. Taking the 17.2 in the biochemical laboratory as the standard and adding 15.8×15% is: 2.37+15.8=18.17mmol/L , and 18.17 is outside the range of 17.71, so sorry, your blood glucose meter is not accurate within the high value range!

People with diabetes may be wondering, why are there such terms as low value range and high value range?

The reason is very simple. If the blood sugar is normal, it is natural that the blood glucose meter will test normal. However, if a patient with diabetes forgets to take medicine or take insulin one day, the blood sugar may soar to 23mmol/L (extremely high value), and the blood glucose meter will be seriously inaccurate in the extremely high value range, which will directly delay treatment.

On the contrary, if a patient with diabetes has diarrhea for several days in a row, cannot eat, and has a blood sugar lower than 3.9, and the patient happens to have asymptomatic hypoglycemia, and the blood glucose meter is seriously inaccurate at the low value, then something big will happen. .

Therefore, the blood glucose meter comparison in the hospital must set at least 5 concentrations, such as sample No. 1 2.1mmol/L, sample No. 2 3.00mmol/L, sample No. 3 10.3mmol/L, sample No. 4 16.7mmol/L, sample No. 5 24.6mmol /L, so that the low value, the middle value, the high value, as well as the extremely low value below 2.2 and the extremely high value above 22.2 are all available, so that we can compare whether there is a problem with the blood glucose meter.

People with diabetes will say that it is so complicated to compare blood glucose meters. If you have this idea, you will be like the two cases at the beginning of the article. It is a rough comparison, but in fact the comparison is really inaccurate.

Is it correct to compare Case 1 and Case 2?

Case 1, the most obvious problem is to compare your own blood glucose meter with the hospital's blood glucose meter. The premise is to ensure that the hospital's blood glucose meter itself performs biochemical comparison as required (diabetes patients can consult the hospital's blood glucose meter when measuring blood sugar. Have your blood glucose meters been compared twice a year? If there is no comparison, then this method needs to be abandoned directly. For example, some community outpatient department blood glucose meters may not have the conditions for standardized comparison).

Case 2 looks like the two blood sugar values are the same, but it is actually a coincidence, because all standard comparisons need to be completed within 30 minutes, while ordinary blood tests for blood sugar, liver function and other items need to be done on the analyzer at once. Test one item at a time, because there are many blood samples in the hospital, and it cannot be completed within 1 to 2 hours. Everyone knows this. Therefore, if you adopt option 2 and the comparison is completed within half an hour, then it is a real comparison.

I would also like to remind everyone that because the test value of the portable blood glucose meter is only a clinical reference, if there is an abnormal low or high blood sugar value, no matter at home or in the hospital, as long as it is measured by the blood glucose meter, blood must be drawn for a biochemical review of blood sugar. , for timely treatment.