1. How to judge hemolysis?
Generally, the specimen after centrifugation is observed to judge whether hemolysis, but sometimes after centrifugation, if it is shaken accidentally, the specimen has a slight red turbidity, which can be regarded as hemolysis if you don't look carefully. So, how can we determine if it is true hemolysis? The best way is to measure the hemoglobin content in the serum, that is, the hemolysis index, to know if there is hemolysis.
Specifically, how to determine whether the sample has undergone clinical hemolysis and hemolysis? The current more conventional method is to judge according to the haemolysis index (haemolysisIndex, or HI). The hemolysis index is actually the level of free hemoglobin in the plasma. Some researchers compared 50 studies on hemolysis, and found that 20 of them use the hemolysis index to define hemolysis, 19 of them used visual inspection, and 11 of them did not indicate the method.
The practice of using visual hemolysis to select clinical samples is considered inaccurate because it lacks objective quantitative standards and does not consider the sensitivity of different indicators to hemolysis. In a study in Crudia in 2018, people carefully followed up 495 blood samples and test results in the emergency room, and found that visual judgment of hemolysis can cause up to 31% of the test results to be inappropriate, including 20.7%. In the case of, hemolysis had an impact on the results but was ignored. In 10.3% of the cases, the test results were suspended but later found not to be affected by hemolysis.
In studies using the hemolysis index, the average limit value of the hemolysis index is 846 mg/L hemoglobin, but the interval is very large, ranging from 150 mg/L to 3000 mg/L. The reason for the large interval is related to the tolerance of different test indicators to hemolysis. At present, on most biochemical instruments, the hemolysis index is already an independent indicator, so that all the blood samples that are tested on the machine can be calibrated for the degree of hemolysis, and the hemolysis index and various clinical indicators can be gradually accumulated in practice. In order to determine the degree of tolerance of various indicators to hemolysis on a quantitative basis.
2. Causes of hemolysis
The cause of hemolysis, from the perspective of whether it is related to the clinical examination process, can be divided into clinical examination-related hemolysis, and non-clinical examination-related hemolysis. Clinical examination-related hemolysis refers to the hemolysis that occurs due to the rupture of red blood cells due to improper operation of the clinical examination. This is the focus of our discussion. Clinical practice and related literature have proved that the occurrence of hemolysis is directly related to the sample collection process. During the clinical examination, if the diameter of the blood sampling needle is too small, the blood sampling speed is too fast, the blood sampling point is improperly selected, the tourniquet is used for too long, Insufficient blood collection tubes, excessive shaking after blood collection, excessive shaking during transportation, etc., will cause hemolysis. It can be subdivided into the following:
Specimen collection
Blood collection injury, such as repeated needle insertion and blood collection at the site of hematoma; blood collection from vascular access devices such as venous indwelling needles, infusion tubes, central venous catheters, and syringe blood collection; the median anterior elbow vein, cephalic vein, and expensive veins are not preferred; fine needles are used; The disinfectant is not dry; the tourniquet has been used for more than 1 minute; it is not mixed in time, vigorously shaken and mixed; the blood collection volume is insufficient, and the vacuum measurement scale of the blood collection tube is not reached; the quality of the vacuum blood collection tube and the separation gel is poor; the large-capacity vacuum blood collection tube is used, etc. .
Of particular note is that in a study in the United States, 853 samples were used to compare two blood collection routes. These two routes are venous vacuum blood collection and venous catheter blood collection. The incidence of hemolysis in blood drawn through venous catheters was found. The rate of hemolysis when the blood is drawn directly from the vein with a needle is 0.3%, and the incidence of hemolysis through the venous catheter is significantly higher than that of direct needle extraction. In another study, the other two conditions were compared, that is, the combination of venous catheter and vacuum blood collection tube. Compared with the direct cooperation of venous catheter and needle, it was found that the incidence of hemolysis in the former was significantly higher. The use of butterfly wing needles can reduce the incidence of hemolysis, regardless of whether it is matched with an intravenous catheter. The use of small-caliber needles (22-gauge needles or smaller) can significantly increase the occurrence of hemolysis. From a number of clinical comparative observations, we can see that the main physical cause of clinical examination-related hemolysis is the excessive shear force in certain steps of the clinical examination, which exceeds the normal blood flow of red blood cells in the body. The stress in the process of changing, thus causing the rupture of the cell membrane. It is precisely because of this principle that the above-mentioned improper operations, such as the diameter of the blood sampling needle is too small, the blood sampling speed is too fast, the blood sampling path is too long, and the excessive vibration during transportation will cause hemolysis.
Specimen transfer
Severe vibration during pneumatic transmission; long transit time; excessively high temperature and severe vibration of the transport vehicle, etc.
Laboratory specimen processing
Specimen preservation time is long; specimen preservation temperature is too high; not centrifuged in time; blood is not completely coagulated before centrifugation; centrifugation temperature is too high and speed is too fast; centrifugation again, etc.
Hemolysis in the body
Autoimmune hemolysis, such as incompatible blood transfusion; genetic and metabolic diseases, such as thalassemia, hepatolenticular degeneration; drug hemolytic reaction after medication, such as acute hemolytic reaction caused by intravenous ceftriaxone sodium; severe infection; diffuse vascularity Internal coagulation; heart stents, artificial heart valves, extracorporeal membrane oxygenation therapy, etc. The hemolysis laboratory of specimens caused by hemolysis in the body shall not be rejected, and the physician shall indicate on the application form.
In addition, non-clinical examination-related hemolysis is caused by pathological reasons, and there are independent detection indicators, because it is not the focus of this article, so I will not repeat it.
3. The influence of hemolyzed samples on clinical examination
There are many factors that affect the accuracy of test results, including before analysis, during analysis, and after analysis. Before the analysis, the influencing factors accounted for a large proportion. After all, we cannot know what the sample went through before it came to the laboratory. Therefore, when we encounter abnormal results, we should analyze them scientifically from the laboratory and clinical perspectives. For unexplainable results, we should communicate with the clinic more. This will help us discover problems in time and re-examine by re-collecting specimens. To solve the problem, a more accurate and reliable test result can be obtained.
Hemolysis has different, quantitative, and significant effects on a number of clinical test indicators. Therefore, while providing the quality of clinical samples and avoiding clinical test-related hemolysis, it is also necessary to fully consider hemolytic factors in the process of clinical analysis The existence and influence of the index, and actively develop the index-related hemolysis index, so as to ensure the validity of the clinical examination data.
