Which of the following would be an acceptable sample for a complete blood count (CBC)?

Acceptable Sample for Complete Blood Count (CBC)

The only acceptable sample for a complete blood count (CBC) is option D - a CBC drawn on a nonfasting patient. The other options present various collection errors that would compromise test results and patient care.

Analysis of Sample Options

Option A: CBC with a small clot in the tube

A clotted sample is unacceptable for CBC testing 1. Clots in the specimen will:

• Trap blood cells, causing falsely decreased cell counts
• Interfere with automated analyzer function
• Lead to inaccurate results that could affect clinical decision-making

Option B: CBC drawn above an intravenous access site

Drawing blood above an IV access site is unacceptable because:

• IV fluids can dilute the sample, causing falsely decreased cell counts
• Medications in the IV line may contaminate the sample
• This practice violates standard phlebotomy protocols that require drawing from the opposite arm or below an IV site

Option C: CBC collected in a green top tube

Green top tubes contain heparin as an anticoagulant, which is inappropriate for CBC testing 1. CBC samples require:

• EDTA (lavender/purple top) tubes as the standard anticoagulant
• EDTA preserves cellular morphology and prevents clotting
• Using the wrong collection tube will invalidate results

Option D: CBC drawn on a nonfasting patient

This is the only acceptable sample. Multiple guidelines confirm that:

• Fasting status does not significantly affect CBC parameters 1
• CBC testing can be performed reliably regardless of when a patient last ate
• No major guidelines require fasting for CBC collection

Importance of Proper CBC Collection

The CBC is one of the most essential and commonly ordered laboratory tests in medicine 2, 3. It provides critical information about:

• Red blood cells, white blood cells, and platelets
• Hemoglobin and hematocrit values
• Cell indices that help diagnose various conditions

Proper collection is vital because:

1. CBC results guide critical clinical decisions in diagnosing and monitoring conditions
2. Inaccurate results from improper collection can lead to misdiagnosis
3. Repeated blood draws due to specimen rejection increase patient discomfort and delay care

Best Practices for CBC Collection

For optimal CBC results:

• Use EDTA (lavender/purple top) tubes
• Fill tubes to the appropriate volume mark
• Gently invert tubes 8-10 times to mix anticoagulant
• Process samples within recommended timeframes
• Avoid hemolysis during collection
• Draw from sites away from IV access

Common Pitfalls to Avoid

• Clotted specimens (partial or complete)
• Hemolyzed samples from rough handling
• Insufficient sample volume
• Improper anticoagulant
• Delayed processing leading to cell deterioration
• Collection from sites contaminated by IV fluids

By following proper collection procedures, healthcare providers can ensure accurate CBC results that appropriately guide patient care decisions.