CNA Medical Lab and Specimen Collection Skills 4

Question 1

A CNA is assisting with a blood draw and notices the tourniquet has been in place for over 3 minutes while the phlebotomist searches for a vein. What is the most critical concern with prolonged tourniquet application at this point?

Accepted Answer

Hemoconcentration, which falsely elevates cellular and protein-bound analyte results

Answer

Tourniquets left on longer than 1–2 minutes cause hemoconcentration: fluid shifts out of the vessel, concentrating red blood cells, proteins, lipids, and certain analytes like potassium and calcium. This directly falsifies lab values. While venous collapse and discomfort are real concerns, the primary laboratory integrity issue is hemoconcentration causing spurious results.

Question 2

A urine specimen collected via clean-catch midstream must be transported to the lab but will not arrive for 90 minutes. The CNA has no ice available. Which action best preserves specimen integrity?

Accepted Answer

Refrigerate the specimen at 2–8°C and transport within the 2-hour window

Answer

Refrigeration at 2–8°C is the standard method to preserve urine specimens when immediate delivery is not possible, inhibiting bacterial overgrowth and cellular degradation for up to 24 hours. Boric acid is a valid chemical preservative but requires specific tubes that a CNA may not independently add without an order. Simply resealing does not prevent degradation, and collecting a new specimen without resolving the transport delay repeats the same problem.

Question 3

During a stool specimen collection for occult blood (FOBT), the patient reports they ate a rare beef steak and took ibuprofen the night before. The CNA should:

Accepted Answer

Notify the nurse and document, because both factors can cause a false-positive guaiac FOBT result

Answer

Guaiac-based FOBT detects the peroxidase activity of heme—it does NOT distinguish human from animal hemoglobin. Red or rare meat contains animal hemoglobin that can trigger a false positive. Additionally, NSAIDs like ibuprofen can cause gastrointestinal microbleeding, also producing false positives. The CNA must notify the nurse and document both findings so the clinician can decide whether to delay testing. Immunochemical FIT tests are human-specific, but guaiac tests are not.

Question 4

A CNA is collecting a sputum specimen for culture and sensitivity. The patient produces a sample that appears watery and clear. What is the most likely problem with this specimen?

Accepted Answer

The specimen is likely saliva contamination rather than true lower respiratory sputum

Answer

True sputum originates from the lower respiratory tract and should be thick, mucopurulent, and sometimes discolored. A watery, clear specimen is characteristic of saliva—an inadequate sample that will yield unreliable culture results, typically showing oral flora. The CNA should instruct the patient to take a deep breath, cough forcefully from the chest, and try again. Saliva contamination is the most common reason sputum specimens are rejected by microbiology labs.

Question 5

When collecting a wound swab for culture, the CNA is instructed to use the Levine technique rather than the Z-stroke technique. What is the key difference in the Levine technique?

Accepted Answer

The swab is rotated with firm pressure over a 1 cm² area of the wound bed for 5 seconds

Answer

The Levine technique involves applying firm pressure while rotating the swab over a 1 cm² area of viable wound tissue for approximately 5 seconds, with enough pressure to express fluid from within the tissue. This method captures deep-tissue organisms rather than just surface contaminants or necrotic debris. The Z-stroke (or Zig-zag) technique samples a broader surface area but is considered less accurate for deep-tissue pathogens. The Levine technique is the evidence-based standard for wound culture collection.

CNA Practice Test

CNA Practice Test

CNA Medical Lab and Specimen Collection Skills 4