Free MLPAO Specimen Processing and Handling Questions and Answers — Questions and Answers
Question 1: A serum separator tube (SST) is received for routine chemistry testing. According to CLSI guidelines, what is the recommended maximum time between collection and centrifugation to ensure specimen integrity?
- 4 hours
- 30 minutes
- 2 hours (Correct answer)
- 6 hours
Correct answer: 2 hours
To ensure the quality and integrity of the specimen, CLSI guidelines recommend that serum separator tubes be centrifuged within 2 hours of collection. Delay beyond this timeframe can lead to changes in analyte concentrations due to ongoing cellular metabolism.
Question 2: An MLA is tasked with preparing aliquots from a primary plasma sample for multiple downstream tests. Which of the following is the MOST critical step to perform immediately before pipetting the plasma into the secondary tubes?
- Gently mix the primary sample by inversion. (Correct answer)
- Ensure the aliquot tubes are pre-chilled.
- Check the primary sample for fibrin clots.
- Verify the patient's fasting status.
Correct answer: Gently mix the primary sample by inversion.
After centrifugation and potential storage, concentration gradients of analytes can form within the plasma or serum. Gently mixing the primary sample by inversion before aliquoting ensures that each aliquot is a homogenous and representative portion of the original specimen, which is crucial for accurate and consistent test results.
Question 3: A cerebrospinal fluid (CSF) specimen is delivered to the lab for cell count, microbiology, and chemistry tests. The sample consists of four sequentially collected sterile tubes, numbered 1 through 4. For the cell count and differential, which tube is typically preferred to minimize contamination from a traumatic tap?
- Tube #2
- Tube #4 (Correct answer)
- Tube #1
- Any tube can be used interchangeably
Correct answer: Tube #4
In a lumbar puncture, the first tube collected may be contaminated with peripheral blood from the puncture itself. Subsequent tubes will have progressively fewer red blood cells if the bleeding was from a traumatic tap. Therefore, the last tube collected (Tube #3 or #4) is preferred for cell counts and cytology to get the most accurate representation of the cells actually present in the CSF.
Question 4: Which of the following conditions is the most common pre-analytical cause of a falsely elevated potassium (K+) level in a serum specimen?
- Lipemia
- Icterus
- Prolonged tourniquet application
- Hemolysis (Correct answer)
Correct answer: Hemolysis
Red blood cells contain a high concentration of potassium. When hemolysis (the rupture of red blood cells) occurs, this intracellular potassium is released into the serum or plasma, causing a falsely high, or pseudohyperkalemic, result that does not reflect the patient's true physiological state.
Question 5: A laboratory receives a specimen for forensic toxicology testing. What is the most crucial documentation that must accompany the specimen from collection to analysis to ensure its legal admissibility?
- A detailed patient clinical history
- A standard laboratory requisition form
- A chain of custody form (Correct answer)
- A signed patient consent form
Correct answer: A chain of custody form
A chain of custody form provides a chronological and unbroken paper trail documenting the collection, handling, transfer, and storage of a specimen. For legal and forensic purposes, this documentation is essential to prove that the specimen was not tampered with, substituted, or altered at any point, ensuring its integrity and admissibility in court.
Question 6: A blood sample for lactate analysis is drawn in a grey-top (sodium fluoride/potassium oxalate) tube. The test cannot be performed immediately. What is the proper short-term storage condition for this specimen to ensure stability?
- Placed in a 37°C heat block
- Left at room temperature on the bench
- Frozen at -20°C
- Refrigerated on an ice/water slurry (Correct answer)
Correct answer: Refrigerated on an ice/water slurry
Sodium fluoride is an antiglycolytic agent that inhibits the enzymatic breakdown of glucose (glycolysis), which produces lactate. However, this process is only slowed, not stopped completely. Chilling the specimen on an ice/water slurry significantly slows down any residual cellular metabolism, preserving the in-vivo lactate concentration until the sample can be centrifuged and analyzed.
