MLS Clinical Procedures & Protocols 2 — Questions and Answers
Question 1: A patient's blood culture bottle flags positive after 18 hours. What is the FIRST action the MLS should take?
- Subculture to blood agar and report Gram stain to clinician (Correct answer)
- Wait 24 hours before taking action
- Discard and collect a new specimen
- Perform susceptibility testing immediately without Gram stain
Correct answer: Subculture to blood agar and report Gram stain to clinician
A positive blood culture flag requires immediate Gram stain and subculture, with results phoned to the clinician as a critical value.
Question 2: Which anticoagulant is used in the light blue (sodium citrate) tube and what is its primary application?
- EDTA; complete blood count
- Sodium citrate; coagulation studies (Correct answer)
- Lithium heparin; chemistry panels
- Potassium oxalate; glucose testing
Correct answer: Sodium citrate; coagulation studies
Sodium citrate chelates calcium to prevent clotting and is the required anticoagulant for PT, aPTT, and other coagulation assays.
Question 3: A urine dipstick shows 2+ protein but the SSA (sulfosalicylic acid) test is negative. What is the most likely explanation?
- The specimen is contaminated with bacteria
- The protein is Bence Jones protein or immunoglobulin light chains (Correct answer)
- The dipstick reagent strip has expired
- The urine pH is too acidic for SSA to work
Correct answer: The protein is Bence Jones protein or immunoglobulin light chains
Dipstick detects mainly albumin, while SSA detects all proteins including Bence Jones proteins; a negative SSA with positive dipstick suggests a false-positive dipstick reaction.
Question 4: During a venipuncture, blood stops flowing into the tube. Which corrective action should be attempted FIRST?
- Remove the needle and start over at a new site
- Slightly advance or withdraw the needle to reposition it (Correct answer)
- Apply a tourniquet more tightly
- Switch to a smaller gauge needle
Correct answer: Slightly advance or withdraw the needle to reposition it
Slight needle repositioning is the first corrective step because the bevel may be against the vessel wall or the vein may have collapsed.
Question 5: Which specimen type is MOST appropriate for detecting anaerobic bacteria?
- Nasopharyngeal swab in Amies transport medium
- Mid-stream clean-catch urine
- Deep wound tissue submitted in an anaerobic transport container (Correct answer)
- Sputum collected in a sterile cup
Correct answer: Deep wound tissue submitted in an anaerobic transport container
Anaerobes die rapidly on exposure to oxygen, so deep tissue submitted in sealed anaerobic transport is necessary for recovery.
Question 6: A hemolyzed serum specimen is received for potassium testing. The MLS should:
- Run the specimen and flag the result as hemolyzed
- Reject the specimen and request a recollect (Correct answer)
- Centrifuge again to remove hemolysis
- Dilute the specimen to reduce interference
Correct answer: Reject the specimen and request a recollect
Hemolysis releases intracellular potassium, falsely elevating serum potassium by up to 20 mEq/L, making the result clinically unreliable.
Question 7: Which procedure is required before performing a finger stick on an infant younger than one year?
- Apply topical EMLA cream for 60 minutes
- Warm the heel for 3–5 minutes and collect from the plantar surface (Correct answer)
- Collect from the fingertip with a lancet shorter than 2 mm
- Use the antecubital vein instead to avoid pain
Correct answer: Warm the heel for 3–5 minutes and collect from the plantar surface
Heel sticks on the plantar (medial or lateral) surface, preceded by warming to increase blood flow, are the standard capillary collection site for infants under one year.
MLS Clinical Procedures & Protocols 2
A patient's blood culture bottle flags positive after 18 hours.
What is the FIRST action the MLS should take?