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The organizing basis for drawing blood is known as the "order of draw."

It is the order in which several blood tubes are filled during a blood collection technique, and it is intended to remove any chance of cross-contamination that can lead to inaccurate results. The accuracy of the test results may be impacted if the blood sample was contaminated with an anticoagulant or preservative from a prior tube. It is also possible to measure or analyze the blood's cells, molecules, proteins, and other components by drawing samples in a specific order.

For multiple-tube collections, the draw is typically conducted in the following order:

1. Blood culture tubes

The growth medium in blood culture bottles promotes the growth of microorganisms while the anticoagulant in the bottles keeps the blood from clotting. The most widely used anticoagulant, sodium polyanethol sulfonate (SPS), does not hinder the growth of the majority of organisms.

2. Coagulation tubes (such as blue-topped Sodium Citrate)

Coagulation tubes (blue top) are filled with a sodium citrate solution that chelates calcium to act as an anticoagulant. Blood clotting requires calcium. Calcium is added to coagulation tests in the lab in order to promote clot formation. Citrate has a low saturation level and can have its effects reversed by the calcium levels in the clotting reagent, making it an effective anticoagulant for clotting studies.

3. Serum tubes (including those with clot activators and gels)

Clinical chemistry, immunology, protein electrophoresis, serology, microbiology, and toxicology do use serum clot activator tubes. A clot activator, which triggers the coagulation process, is particularly coated on the inner wall of the Serum Clot Activator tube.

4. Heparin tubes (green-topped tubes)

Plasma can be produced using lithium or sodium heparin tubes for biochemical testing. There is also a gel separator option for the heparin tubes. Clinical chemistry and trace mineral testing are included in the range of applications that heparin tubes can be used.

5. EDTA tubes (lavender-topped tubes)

The commonest anticoagulant found in blood collection tubes is EDTA. Both a dry form and a solution are possible. Blood must be collected up to a certain spot on the tube due to the quantity and concentration of EDTA. Dilution of the sample may occur with parameter changes if insufficient blood is obtained.

By attracting calcium ions and preventing the blood sample from clotting, EDTA functions as an anticoagulant. For the majority of hematology operations, including determining the complete blood count, making EDTA plasma, collecting whole blood, and obtaining bone marrow samples, EDTA is employed.

It is essential to follow the proper order of draw to ensure accurate test findings and prevent sample contamination. To guarantee the integrity of the blood sample and the reliability of the test results, healthcare personnel should be instructed in the correct order of draw and should consistently adhere to it.

According to international guidelines, blood should be drawn in the following order: blood culture bottle, non-additive tube, coagulation tube, clot activator, serum separator tube, sodium heparin, plasma separator tube, ethylenediaminetetraacetic acid (EDTA), blood tube, and oxalate/fluoride. This is done to prevent cross-contamination between the various additives contained in blood collection tubes.

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