Selecting the right anticoagulant for blood collection vessels to make the test results more reliable

In clinical blood testing, the selection of anticoagulants is a key factor that directly affects the accuracy of the test results. Different anticoagulants have different mechanisms of action and scope of application, and incorrect selection may lead to nucleic acid degradation, pseudoprolongation of clotting time, or measurement deviation of blood cell volume. Understanding the characteristics and limitations of various anticoagulants can help make more reasonable judgments during the testing design phase.

Why does whole blood nucleic acid extraction avoid heparin

Heparin lithium and heparin sodium are commonly used anticoagulants, but they have significant limitations in blood collection for nucleic acid extraction purposes. Heparin binds to membrane proteins on the surface of the cell membrane, causing changes in membrane permeability that may affect subsequent nucleic acid release efficiency. Heparin can also bind and activate various proteasomes and complement systems in whole blood, producing a series of enzymatic effects that can easily lead to nucleic acid degradation and reduce the acquisition rate of nucleic acids. The effect of extracting nucleic acids from heparin anticoagulated whole blood samples stored at room temperature is often unsatisfactory.

The interference of heparin is not only limited to the extraction stage, but also affects subsequent PCR detection. Heparin may affect the activity of DNA polymerase or interfere with the accuracy of magnesium ion concentration in the reaction system, leading to a decrease in amplification efficiency or the appearance of non-specific bands. Therefore, heparin is not an ideal choice in scenarios involving nucleic acid extraction and amplification testing.

 Selection of Sodium Citrate Concentration in Coagulation Testing

Sodium citrate is the standard anticoagulant in coagulation function testing. There are two concentrations of sodium citrate solutions, 3.2% and 3.8%, available on the market. Although it was initially believed that both could be used, practical verification has shown that the 3.8% concentration of anticoagulant poses more risks. 3.8% anticoagulants are more likely to cause false prolongation in calcium dependent coagulation tests such as PT and APTT, especially in cases where the sample size is insufficient or the red blood cell ratio is high, resulting in a relative decrease in plasma volume. If the ratio of anticoagulants to blood exceeds the recommended ratio of 1:9, higher concentrations of anticoagulants will further exacerbate this deviation.

In the vast majority of clinical scenarios, a concentration of 3.2% sodium citrate is a more reliable choice. Only in special blood samples with very few red blood cells, a concentration of 3.8% shows certain advantages. But this rare situation can be solved by adjusting the proportion of anticoagulants, and there is no need to change the concentration commonly used for small probability scenarios. Therefore, after clinical practice testing, the 3.2% concentration of sodium citrate has gained wider recognition.

The effect of EDTA salt on blood cell volume

EDTA salts exhibit excellent anticoagulant effects, but they are not without interference. All EDTA salts can cause blood cell shrinkage, thereby affecting the trace hematocrit after centrifugation. The difference between different EDTA salts is reflected in their solubility, with potassium EDTA having a higher solubility than sodium EDTA, making potassium EDTA more commonly used.

The pH values of EDTA disodium salt and EDTA dipotassium salt are relatively lower than EDTA tripotassium salt. In this acidic environment, cells will swell, and this swelling effect can partially compensate for cell shrinkage caused by osmotic pressure. For the calibration of electronic blood cell counters, using EDTA disodium salt and EDTA dipotassium salt as anticoagulants yields hematocrit values that are closer to the true values than using EDTA tripotassium salt. This difference is worth noting in scenarios where precise measurement of average blood cell volume is required.

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