In the hospital, a tube of blood can detect multiple indicators, why do you always repeat the blood draw every day? For this problem, I believe that many friends who have been hospitalized in the hospital will have such a question. Especially for patients who have just gone through the admission procedures, they have to draw a lot of blood at the beginning, there are red tubes, there are blue tubes, there are purple tubes, there are black tubes, there are orange tubes, etc., some even draw a few tubes of the same color, a blood draw to draw 7, 8 or even more than 10, the next day to continue to draw. Some people always ask why so much blood is drawn? Even think that the doctor draws so much blood is not to sell?
( Multiple tubes of blood samples are required for one test )
As a laboratory doctor, it is really necessary to explain this situation to everyone and answer everyone's doubts. After all, every blood sample is eventually sent to our laboratory department for testing, and we are most familiar with the requirements for blood samples. Why is it possible to test all items with one tube of blood? Why do you have to repeat the blood draw every day? I'll answer them all.
The first question: Why can't all items be tested with one tube of blood?
(Different collection blood vessel anticoagulants are different)
● Reason one, different items determine different specimen types There are many laboratory examination items, which can reach hundreds of test items, and different test items will be different for the types of specimens. Clinically, there are three main types of specimens: whole blood, serum and plasma.
(for whole blood specimens)
Whole blood samples: Anticoagulant whole blood must be used to determine the red blood cell component, and the anticoagulants added to these specimens are EDTA salt, heparin, or citrate, and the test items for each anticoagulant are also different. For example, the specimen of EDTA salt anticoagulant whole blood is used to detect cell analysis, which is what we often call blood routine, and the drawn blood vessels used are purple tubes, mainly to check red blood cell counts, white blood cell counts and classification, hemoglobin, platelet counts, etc.; heparin anticoagulant whole blood is a green blood vessel draw, mainly used to determine blood gas analysis, calcium, magnesium, zinc plasma; citric acid anticoagulation whole blood is a black blood vessel, mainly used to determine platelet function and esosomes.
(for serum specimens)
Serum specimens: is not added to the anticoagulant, blood natural coagulation after high-speed centrifugation of the supernatant, blood samples are generally red tubes or yellow tubes with separating glue, most of the clinical biochemical indicators are detected with serum, such as liver function, myocardial enzyme profile, biochemistry, electrolytes, blood lipids, preoperative four, five items of alpha work, serum protein electrophoresis, lipoprotein electrophoresis, rheumatoid factors, etc. In addition, serum specimens are also used for antibody testing of pathogenic microorganisms, such as hepatitis virus antibodies, pertussis antibodies, EB antibodies, syphilis antibodies, etc.
(for plasma specimens)
Plasma specimens: it is a specimen with an anticoagulant, and the supernatant obtained after high-speed centrifugation also contains a coagulation factor. The samples drawn are usually blue tubes, and the anticoagulant added to them is a sodium citrate anticoagulant (1:9). It is mainly used to detect thrombin function, including prothrombin time, activated partial prothrombin time, fibrinogen, antithrombin, D-dimer, etc.
●Reason 2: Different anticoagulants will have a certain impact on the test results
The purpose of adding anticoagulants to the specimen is to inhibit blood aggregation so that the components to be measured in the blood sample do not change significantly before analysis. However, the anticoagulant added to each pumping vessel is different, and the principle of anticoagulation is also different.
(Anticoagulants are different and have an impact on the results of the test)
EDTA: by forming a stable chelate with calcium ions in the aqueous phase to prevent blood clotting, EDTA salts include potassium, sodium, lithium salts, clinical complete blood counts generally use EDTA potassium salts. However, EDTA can affect the activity of certain enzymes and inhibit lupus erythematosus factor, so it is not suitable for making histographic stains and blood smears that examine lupus erythematosus cells. In addition, EDTA also affects platelet function testing, so it is not suitable for platelet function testing.
Heparin: The principle of heparin anticoagulation is mainly to strengthen the inactivation of antithrombin III, thereby preventing the formation of thrombin, and the salts of heparin are sodium, lithium and ammonium. Because sodium heparin can increase the content of sodium in plasma, heparin ammonium can increase the content of urea nitrogen, so some biochemical components in the serum and heparin anticoagulated plasma have obvious differences, will have a certain impact on the results. In addition, heparin excess can also cause white blood cell aggregation and thrombocytopenia, so it is not suitable for white blood cell classification and platelet count, and it is not suitable for hemostasis tests.
Citrate: The anticoagulant principle of citrate is that citrate forms a soluble chelate with calcium ions in the blood, thereby preventing blood from clotting. It is mainly used for hemostasis tests and the determination of erythrocyte sediment rate. The ratio of anticoagulants to blood is used 1:9 in the blood vessel, and this ratio cannot be changed arbitrarily, otherwise it will have a certain impact on some test results.
Therefore, different anticoagulants will have a certain impact on the test results, and the use of the wrong anticoagulant will affect the authenticity of the test results. Such as aspartamidominotransferase, carcinoembryonic antigen, iron ions, uric acid, etc., the determination value of EDTA anticoagulant plasma is lower than the measurement value of heparin anticoagulant plasma.
In addition, anticoagulant solution or dry powder will also have an impact on the results, heparin sodium solution will produce a dilution effect, so that the blood gas analysis, electrolyte, lactate determination level decreases, in order to avoid the dilution effect of anticoagulant solution, heparin powder anticoagulation should be used.
●Reason 3: The results of serum and plasma tests used in biochemical testing projects will vary
(Serum differs from plasma in composition)
For biochemical testing projects, many laboratories always use serum specimens for testing, but in fact, the detection values of some indicators in the serum will be significantly higher than the true values of the body. Such as alanoaminotransferase, apolipoprotein A1, apolipoprotein B, etc., and some indicators will be significantly lower than the body value, such as blood glucose, total protein and so on. There are also differences in glucose measured with intravenous whole blood and glucose measured in serum and plasma. If the laboratory chooses to use intravenous whole blood to determine glucose, the plasma glucose value should be obtained by multiplying by a correction factor of 1.11. In addition, the World Health Organization has made it clear that the use of serum to determine blood glucose concentrations is not allowed.
Therefore, from the above analysis, it can be seen that the various items measured in the clinical laboratory cannot use the same blood, and the appropriate anticoagulant must be selected in order to provide correct and effective test results for the clinic. And a blood specimen capacity is limited, when centrifuged plasma or serum is only about 55% to 60% of the total blood, when the detection of too many items plasma may not be enough to use the amount of serum; coupled with the implementation of scientific management of the laboratory department now, each specimen has a bar code item distinction, which can effectively improve work efficiency and speed up detection.
Second question: Why do you have to repeat the blood draw every day?
During the hospitalization, it is also a time for the diagnosis and treatment of the disease, during which the doctor needs to have a full understanding of the diagnosis, development and treatment of the disease. A comprehensive test is done at the time of admission to understand the health of the body, and the medication and course of the disease during hospitalization also need to be understood. The purpose of daily blood draw is to understand the diagnosis and development of the disease, guide clinical medication, and understand whether the medication is effective through monitoring changes in testing items. For example, patients with cerebral infarction or myocardial infarction, after taking the drug, they should check the corresponding items by drawing blood to understand how the thrombolysis is, and then use drugs for the course of the disease.
(The glucose tolerance test requires several blood draws to complete one test)
In addition, there are some test items that need to be detected several times to meet the testing requirements, such as glucose tolerance testing, which needs to detect the blood glucose value of 4 to 5 time periods in order to have a full understanding of the situation of glucose tolerance, which requires 4 to 5 consecutive blood samples. Finally, especially for some ICU patients, it is necessary to always pay attention to their clinical indicators, which also require daily blood tests to monitor the change of course and outcome. In general, drawing many blood samples at a time or requiring blood samples to be tested every day is a clinical need, and there is no increase in the burden on the patient or waste of blood.
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