ASCP Phlebotomy Technician Order of Draw and Additives 3 — Questions and Answers
Question 1: Which anticoagulant inhibits thrombin and is used in green-topped tubes?
- EDTA
- Sodium citrate
- Heparin (Correct answer)
- Sodium fluoride
Correct answer: Heparin
Heparin (lithium or sodium) is found in green-topped tubes and works by inhibiting thrombin through activation of antithrombin III.
Heparin is a naturally occurring mucopolysaccharide that enhances the activity of antithrombin III by approximately 1,000-fold, rapidly inactivating thrombin and Factor Xa. Green-topped tubes come in lithium heparin (most common for chemistry) and sodium heparin (used when lithium levels are tested) varieties.
Question 2: What would happen if an EDTA tube were drawn before a chemistry (red/gold) tube in the order of draw?
- No effect on test results
- Falsely elevated potassium and decreased calcium in the chemistry specimen (Correct answer)
- Falsely elevated glucose levels
- Falsely decreased white blood cell count
Correct answer: Falsely elevated potassium and decreased calcium in the chemistry specimen
EDTA carry-over into a chemistry tube would introduce excess potassium (from K-EDTA salts) and chelate calcium, producing falsely elevated potassium and decreased calcium results.
K2-EDTA or K3-EDTA contains potassium as its cation, directly adding potassium to the specimen. EDTA also chelates calcium and magnesium, causing falsely decreased results. EDTA can additionally inhibit metalloenzymes such as alkaline phosphatase, producing falsely low results.
Question 3: Royal blue-topped tubes are used for which type of testing?
- Coagulation studies
- Trace element and heavy metal analysis (Correct answer)
- Blood cultures
- Complete blood count
Correct answer: Trace element and heavy metal analysis
Royal blue-topped tubes are specially manufactured for trace element and heavy metal testing because they are certified to contain no detectable amounts of these metals.
Royal blue-topped tubes are manufactured under strict quality controls to be free from trace metal contamination. They are used for testing lead, zinc, copper, selenium, chromium, arsenic, mercury, and other heavy metals. Standard tubes contain detectable levels of these metals that would contaminate specimens.
Question 4: Why is potassium oxalate paired with sodium fluoride in gray-topped tubes?
- Both are anticoagulants that work synergistically
- Sodium fluoride preserves glucose while potassium oxalate prevents clotting (Correct answer)
- Potassium oxalate kills bacteria while sodium fluoride preserves cells
- They are paired randomly by the manufacturer
Correct answer: Sodium fluoride preserves glucose while potassium oxalate prevents clotting
Sodium fluoride serves as the antiglycolytic agent to preserve glucose, while potassium oxalate serves as the anticoagulant to prevent clotting.
Potassium oxalate prevents blood from clotting by precipitating calcium ions as insoluble calcium oxalate crystals. Sodium fluoride inhibits the enzyme enolase in the glycolytic pathway, preventing cells from consuming glucose for up to 24 hours. Together, they keep blood liquid and preserve glucose levels.
Question 5: A lab test order requires a specimen in a tube with no additives. Which tube should the phlebotomist select?
- Gold-topped SST tube
- Red glass tube (no additive) (Correct answer)
- Light blue-topped tube
- Green-topped tube
Correct answer: Red glass tube (no additive)
A red glass tube (plain red top with no clot activator) contains no additives and allows blood to clot naturally.
Plain red glass tubes are completely free of additives, unlike gold-topped SST tubes (which contain clot activator and separator gel). The glass surface provides some natural activation of clotting. These tubes are used for specific tests such as drug levels and certain serological tests.
Question 6: If a phlebotomist needs to draw both a light blue tube and a lavender tube, how many inversions should each tube receive after collection?
- Light blue: 3-4 inversions; Lavender: 8-10 inversions (Correct answer)
- Both should receive exactly 5 inversions
- Light blue: 8-10 inversions; Lavender: 3-4 inversions
- Neither tube requires mixing
Correct answer: Light blue: 3-4 inversions; Lavender: 8-10 inversions
Light blue tubes require 3-4 gentle inversions while lavender EDTA tubes require 8-10 inversions to ensure thorough mixing.
Light blue (citrate) tubes require only 3-4 gentle inversions because sodium citrate is a liquid anticoagulant that mixes readily. Lavender (EDTA) tubes require 8-10 inversions because EDTA is spray-dried onto the tube walls and needs more mixing to dissolve. Green (heparin) tubes require 8-10, red/SST tubes require 5, and gray tubes require 8-10 inversions.
ASCP Phlebotomy Technician Order of Draw and Additives 3
Which anticoagulant inhibits thrombin and is used in green-topped tubes?