Lab Testing for BB

Question 1

Describe the 2 acceptable specimen samples used in blood bank to include:

a. Color of tube top

b. Anticoagulant present (if any) and how it works

c. Presence or absence of complement in the sample

Answer 1

a. Color of tube top
1. Purple or pink
2. Red

b. Anticoagulant present (if any) and how it works
• Purple/Pink: EDTA is present in the purple and pink top collection tubes – EDTA chelates calcium ions which prevents the activation of the C’ classical pathway

No difference between the purple and pink top tubes – just a visual difference for phlebotomists

• Red top: no anticoagulant present

c. Presence or absence of complement in the sample
• Purple/Pink: no Complement present
• Red top: Complement present

C’ remains active for ~ 24-48 hrs. stored at 4C

Question 2

2. Explain how to correctly “read” a blood bank test.

Answer 2

• Most tubes require centrifugation before interpreting reactions
• Examine for hemolysis first – if present, it would be considered a Positive reaction
• Face cell button towards you, then tilt tube horizontally to observe cells (probably a Negative reaction if cells are
falling without shaking)
• Gently shake tube using a mirror and light source to observe for agglutination

Question 3

3. Describe the grading system used in blood bank to interpret Ag-Ab reactions (4+ - 0).

Answer 3

• 4+ = one large agglutinant; clear background
• 3+ = several large agglutinants; clear background
• 2+ = medium agglutinants; clear background
• 1+ = small agglutinant with cloudy background
• +w = very small macroscopic agglutinants
• +m = microscopic agglutinants (would not use this grade as we are not using microscopes in this module)
• +H = Hemolyzed
• 0 = Negative, no agglutination