Factors affecting accuracy of blood cell analyzer

Factors affecting accuracy of blood cell analyzer

First, the effect of specimen processing methods on the results.

1. Blood collection

Blood analysis usually requires anticoagulation of venous blood, as far as possible without peripheral blood sampling. Because different parts of the skin puncture blood cell composition and cell-to-plasma ratio is often inconsistent, and venous blood is more different. From a technical point of view, capillary blood collection is less, automatic blood analyzer needs more blood, it is difficult to collect enough blood, and can not be repeated when needed, so in addition to a small number of venous blood such as infants, patients with extensive burns and some cases that need frequent blood collection, such as leukemia Venous blood should be used in patients with tumor radiotherapy or chemotherapy.

2. Choice of containers

Anticoagulant containers should be kept as close as possible to prevent water evaporation or environmental pollution. In order to reduce the effect of platelet analysis, a plastic test tube should be used. After blood collection, it should be mixed immediately. If glass products are used, the containers should be silicified first to prevent platelet adhesion and reduce platelet counts. Vacuum blood collection system is widely used in developed countries. This system makes the specimen completely isolated from the outside world during blood collection and testing, avoids air or foreign bodies contaminating the blood, prevents hemolysis, improves detection accuracy, and also prevents blood collection and testing personnel from being infected by direct contact with the blood.

3. Anticoagulant

The anticoagulant recommended by the International Commission for Standardization of Blood (ISCH) is EDTA potassium, which is 1.5-2.2 mg/ml in blood. The anticoagulant has no effect on white blood cell count and size, has the least effect on red blood cell morphology, and can inhibit platelet aggregation.  EDTA disodium for routine blood test and EDTA potassium anticoagulation results compared with no significant change, but its solubility is low, anticoagulation speed is slow, not suitable for the anticoagulation of peripheral blood.

It should be noted that EDTA potassium can make erythrocyte volume swell slightly, MPV is very unstable in a short time after blood collection, after half an hour tends to be stable. Citrate anticoagulants have minimal effect on MPV and other coagulation factors, and can be used for platelet analysis.

4. Diluted specimen

When using a semi-automatic blood analyzer, the blood needs to be pre-diluted before it can be tested, and special attention should be paid to the phenomenon of dilution and hemolysis. Diluted hemolysis refers to the phenomenon that the blood cells dissolve spontaneously with the prolongation of time after high dilution. So blood dilution should be determined as soon as possible, so as to avoid less quantity.

5. The influence of haemolysis samples on the analysis results.

Due to improper specimen handling, such as blood collection is not smooth, violent vibration, etc., can cause hemolysis in the specimen test tube. Samples with severe hemolysis can cause a decrease in hematocrit and hemoglobin, resulting in an increase in MCH and MCC, while the average volume of red blood cells is normal.  This result can make the clinician's role wrong judgment and cause adverse consequences. So for hemolytic specimens, we should re collect specimens and determine them.Meilun

6. Effect of storage time on results

Anticoagulant whole blood at room temperature for instrumental determination, red blood cells, white blood cells and platelets can be stable 24 hours, white blood cell classification can be stable 6-8 hours, hemoglobin can be stable for several days. However, if white blood cells are classified under a microscope, the morphology of granulocytes changes after two hours, so if microscopic examination is necessary, blood tablets should be prepared as soon as possible. Although 4 degrees Celsius can prolong the blood storage period, but platelets should not be stored at low temperature, will affect the count and volume, so if not timely detection of blood should be stored at room temperature.

Many literatures reported that the venous blood with EDTA salt anticoagulation was unstable in detecting MPV within one hour after blood collection. The platelet volume gradually increased by about 20%. After one hour, it tended to be stable, and the change was less than 3% within 1-6 hours. This is because the shape of platelets changes from concave to spherical and the volume increases when the blood is mixed with EDTA salt anticoagulant. So the accuracy of the results should be measured in an hour.

Our monitor manufacturer found that EDTA anticoagulant peripheral blood should also be measured at least 15 minutes later, because during this period of time some samples of platelet temporary aggregation phenomenon, so that the false reduction of platelet counts, not only affects the accuracy of other platelet indicators, but also causes the increase of white blood cell counts. The histogram of platelet and leukocyte volume distribution was also abnormal. The histogram of normal distribution could be obtained after a period of time.

7. Dosage of hemolytic agents and hemolysis time

The automatic hematology analyzer can control the amount of hemolytic agent and the time of hemolytic action. But when using semi-automatic blood cell counter to count blood cells, it is necessary to add hemolytic agent artificially after blood pre-dilution, and then count and classify blood cells after hemolysis. It is very important to master the amount of hemolytic agent and hemolytic time correctly. If the dosage is insufficient or the time after adding is too short, it can cause incomplete hemolysis, so that undissolved red blood cells count into white blood cells, resulting in false increase in white blood cells. Hemolysis does not completely affect the accuracy of hemoglobin. If the dosage of hemolysis is too much or the time of storage is too long, the white blood cells are obviously deformed, so that the white blood cell histogram is abnormal, the result of white blood cell classification and counting is not accurate, or even can not be classified and counted.Meilun

Two. Effects of physiological state and other factors on experimental results

1. Physiological state

In addition to many pathological conditions, the blood cell count can be induced.