The health industry has special blood collection tubes that are used for specimen collection. The glass or plastic tubes mostly consist of various sizes with color-coded tops. Phlebotomists collect 3-10mls of blood depending on the size of the blood collection tube.
The colored caps represent the contents of the vacutainers. Majorly, each tube either contains an anticoagulant or a clotting factor. However, some companies manufacture plain vacutainers for clotting purposes albeit a slow process.
1. Red top tube
While most manufacturers add clotting activating agents into the tube, some companies produce plain ones. The most common clot activator is micronized silica. 6mls of blood mixed five times for adults and 0.5mls for pediatrics is appropriate for most biochemistry tests and some transfusion procedures which require serum. the mode of action of the red top collection tube is the promotion of clotting through the silica particles or glass
Some of the laboratory application for the sample collected include red blood cell phenotyping, glucose, cholesterol, triglycerides, HDL, ionized calcium, potassium, amylase, alkaline phosphatase, drug levels, and viral markers tests. The plain tubes are also used as secondary test tubes for aliquoting. Red-top samples are however rarely used for cold agglutinins, cryoglobulins, and fluoride.
2. Purple/Lavender top tube
These tubes contain anticoagulants, specifically Ethylenediaminetetraacetic Acid (EDTA). The specimen is usually a minimum of 3mls whole blood mostly used in hematological tests such as ESR, and most of the molecular genetics tests. The anticoagulant in the purple top blood collection tube prevents clotting by removing calcium from the blood, a process called chelation.
3. Pink top tube
The tube contains EDTA anticoagulant. Nevertheless, in the lab, the sample can only be used for cross-match purposes.
During manufacture, It is spray-coated with either K2 or K3.
4. Light blue top tube
The tube contains a reversible anticoagulant which is 3.2% buffered 9N sodium citrate that binds and removes calcium hence disrupting the clotting cascade. Nonetheless, calcium can be added back into the inactivated blood to study coagulation under controlled conditions.
2.7mls of blood is put in the tube to ensure that the critical anticoagulant to blood ratio is maintained and the sample mixed three to four times. The machines in the lab are specifically calibrated to interpret results based on a set ratio of blood to anticoagulant. There is usually a mark to indicate the amount of blood to be collected.
Tests that use blood from this tube include:
- Coagulation studies such as Prothrombin Time (PT) which evaluates the extrinsic system and monitors coumadin therapy;
- INR which is calculated from PT to monitor warfarin patients, APTT/ PTT (Activated Partial Thromboplastin Time) which evaluates the intrinsic system and monitors heparin therapy;
- Activated partial thromboplastin ratio (APTR) that is calculated from APTT to monitor patients on intravenous heparin infusions, FDP (Fibrinogen Degradation Products);
- fibrinogen assay for common pathways, TT (Thrombin Time), D-dimer for thrombosis which could be due to DVT or PE, Anti-Xa assay that monitors patients on high-dose low molecular weight heparins eg tinzaparin and factor assays.
The sample can also be used in clinical chemistry and hematology. It is seldom used to check for specific clotting factors e.g. factor VIII, factor IX, Von Willebrand factor, thrombophilia screen, and lupus anticoagulant.
The first few milliliters of blood drawn after a venipuncture is usually activated and therefore a citrated tube should never be the first. It is preferable to collect a discard tube first if only citrated blood is required. Some tests are time-sensitive and should be done at specific periods. For instance, anti-Xa assays must be taken 3-4 hours after tinzaparin is given while INRs are done in the morning.
5. CTAD (Also Light Blue)
The CTAD sample collection tubes contents inhibit ex vivo activation of platelets, making them useful for some more sensitive platelet function and coagulation studies. CTAD is light-sensitive hence stored in the dark. CTAD (blood collection tube) stands for Citrate, Theophylline, Adenosine, and Dipyridamole.
6. Yellow top tube
The tube contains the anticoagulants Acid Citrate Dextrose (ACD) and Sodium Polyanethol Sulfonate (SPS). Besides preventing blood clotting, the additives stabilize bacterial growth. The specimen is appropriate for blood and body fluids cultures and blood grouping. For instance, specimens in SPS containing tubes are suitable for HLA, DNA, and Paternity tests.
The SPS also stops or slows down the action of certain antibiotics, the complement system, and phagocytes hence aiding in the recovery of microorganisms. On the other hand, tubes with ACD are for tissue studies at the cellular level, HLA typing, and paternity testing. The phlebotomist collects approximately 6mls of blood and swirls the contents of the tube about eight times to ensure proper mixing. The blood to CPDA ratio is usually 6:1.
7. Grey top tube
These blood collection tubes contain two additives. Potassium oxalate or K3EDTA is the anticoagulant that removes calcium while sodium fluoride ensures that there is no further glucose breakdown after sample collection. Some grey bottles contain EDTA instead.
The sample is useful in biochemistry for glucose/sugar, lactate, and Glucose tolerance tests (GTT). On legal grounds, blood ethanol can also be examined. Collect 2mls of blood and mix by gently swirling eight times.
8. Green top tube
4mls blood sample mixed eight times yields whole blood and heparinized plasma due to the heparin additive. The additive can be constituted with sodium (dark-green), ammonium or lithium (light-green). The mode of action is blocking the coagulation process by activating antithrombins.
The sample is fitting for tests such as ammonia, carboxyhemoglobin, and STAT electrolytes, karyotyping, insulin, renal screen, renin, FISH, and aldosterone. Infrequently, the sample can be used to test for amino acids, aluminum, homocysteine, gut hormones, and chromosomal tests. However, heparin interferes with PCR reactions. Besides, the sample is not reliable when assessing sodium levels.
9. Light-green tube-plasma separator tube (PST)
These blood collection tubes contain lithium heparin and Polymer gel for plasma separation. It is appropriate for biochemistry tests requiring separated heparinized plasma. However, it is unreliable when assessing lithium levels.
10. Black-top tube
The test tubes contain 3.8% buffered sodium citrate (4NC) which removes calcium by forming salts. The sample, which is 1.6mls blood, is, therefore, suitable for pediatric and Westergren ESR.
11. Royal blue top tube
Some manufacturers include potassium EDTA or sodium EDTA and sodium heparin additives in these blood collection tubes while others make plain tubes. 6mls of blood gently mixed eight times yields serum fit for tests involving toxicology, trace elements, for example, mercury, copper, zinc, and lead and nutritional chemistry. The anticoagulants in royal blue blood collection tubes prevent thrombin formation.
12. Pearl white-top tube plasma preparation tube (PPT)
The vacutainer has EDTA and special polyester material. It is used to obtain plasma for PCR tests. The tube is filled with blood and gently inverted 8-10 times. Plasma for PCR tests is collected in Pearl-White top plasma preparation tubes.
13. Gold top tube
This is a serum separator tube (SST). It contains a clot activator and a gel that separates the cells from the serum. After mixing 5mls of blood five times, letting it stand for 20-30minutes and centrifuging for 10minutes, the sample is appropriate for Chemistry, microbiological serology and immunohematological studies just like the red top sample.
However, some tests are sensitive and therefore specific to the red top. The frozen serum is put in plastic vials as it is not advisable to freeze the SST tube.
14. Capillary tube
15. Blood culture bottles
About 10mls of blood is collected aseptically into the sterile bottles and inverted eight times for fungal and bacteriological studies. The bottles contain culture media that encourage the growth of bacteria in the blood. For instance, BACTEC PLUS (blue label), facilitates the growth of aerobic bacteria, BACTEC LYTIC (purple label) anaerobic organisms and black lid mycobacterial cultures.
16. Cell-free DNA tubes
10mls of blood is drawn, mixed 10 times and cell-free plasma DNA obtained. The tube contains K3EDTA and cell preservative in a liquid medium which stabilizes nucleated cells by inhibiting the release of genomic DNA. Cell-free DNA and genomic DNA are stable for up to 14 days at 6 °C to 37 °C while circulating tumor cells (CTCs) are stable for up to 7 days at 15 °C to 30 °C.
The sample can be used in drug discovery, development of diagnostic assays, and clinical research studies for cancers. Nonetheless, the sample should be handled under the right conditions to avoid diluting the circulating tumor DNA.
17. Blood gases ABGs
Blood collection is done using a syringe and needle containing heparin to check for potassium, oxygen and lactate levels as well as acid-base balance. It is viable for 10minutes.
18. Microtainertubes (pediatric bullet tubes)
|Color||Gold||Red||Light Green (amber or clear)||Lavender||Light Green (without gel barrier)|
|Additive||No additive w/ gel barrier||No additive||Lithium Heparin w/ gel barrier||K2EDTA||Lithium Heparin without gel barrier|
|Volume||0.5 mL||0.5 mL||0.5 mL||0.5 mL||.04 mL|
Order of blood collection according to test type:
- Blood culture
- Light-blue top tube
- Yellow top tube (ACD)
- Cell-free DNA tube
- Red top
- Pediatrics tube
- Gold top tube
- Royal blue top tube
- Green top tube
- Pink top tube
- Lavender top tube
- Pediatrics tube
- Blue top tube (Trace element K2EDTA)
- Grey top tube
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