Medical Laboratory Technician Laboratory Operations and QC Questions and Answers — Questions and Answers
Question 1: An MLT reviewing a Levey-Jennings chart for a daily glucose control run notices that the last two consecutive data points are outside the +2 SD limit. Which Westgard rule has been violated?
- 1_3s
- R_4s
- 2_2s (Correct answer)
- 4_1s
Correct answer: 2_2s
The 2_2s rule is violated when two consecutive control values fall on the same side of the mean and are beyond 2 standard deviations (+2s or -2s). This is a rejection rule that indicates a systematic error in the testing process.
Question 2: A phlebotomist collects specimens for coagulation studies (light blue top), a complete blood count (lavender top), and a chemistry panel (serum separator tube - SST). If the tubes are drawn in the order of SST, lavender, and then light blue, which test result will most likely be falsely elevated?
- Prothrombin Time (Correct answer)
- Hemoglobin
- Serum Potassium
- Blood Glucose
Correct answer: Prothrombin Time
The correct order of draw is critical to prevent additive cross-contamination. The lavender top tube contains EDTA, a potent anticoagulant that works by chelating calcium. If the lavender tube is drawn before the light blue (sodium citrate) tube, trace amounts of EDTA can be carried over into the citrate tube. This contamination will chelate the calcium in the sample, which is essential for the coagulation cascade, leading to a falsely prolonged (elevated) Prothrombin Time (PT) and aPTT.
Question 3: To find comprehensive information regarding the hazards, safe handling, and emergency procedures for a new chemical reagent, an MLT should primarily consult the:
- Laboratory's Standard Operating Procedure (SOP)
- Annual CAP inspection checklist
- Instrument operation manual
- Safety Data Sheet (SDS) (Correct answer)
Correct answer: Safety Data Sheet (SDS)
The Safety Data Sheet (SDS), formerly MSDS, is a document mandated by OSHA that provides detailed information about a hazardous chemical. It includes properties, health hazards, protective measures, and safety precautions for handling, storing, and emergency response.
Question 4: A laboratory is validating the precision of a new assay. A control material is analyzed 20 times, yielding a mean value of 80 mg/dL and a standard deviation (SD) of 4 mg/dL. What is the coefficient of variation (CV)?
- 2.0%
- 5.0% (Correct answer)
- 20.0%
- 0.5%
Correct answer: 5.0%
The coefficient of variation (CV) is a measure of relative variability. The formula is CV (%) = (Standard Deviation / Mean) × 100. For this data: (4 mg/dL / 80 mg/dL) × 100 = 5.0%.
Question 5: Under the Clinical Laboratory Improvement Amendments (CLIA), which of the following is a key requirement for laboratories performing moderate and high-complexity testing but NOT for those performing only waived testing?
- Following the manufacturer's instructions for test performance.
- Successful participation in an external proficiency testing (PT) program. (Correct answer)
- Maintaining a log of all patient results.
- Having a designated area for performing laboratory tests.
Correct answer: Successful participation in an external proficiency testing (PT) program.
CLIA regulations require laboratories performing moderate and high-complexity tests to enroll and participate successfully in an approved external proficiency testing (PT) program. PT is used to verify the accuracy and reliability of a laboratory's testing. Laboratories that perform only waived tests are not required to participate in PT, although they must follow manufacturer's instructions.
Question 6: A technologist notes that all patient and quality control results for an analyte measured by spectrophotometry are significantly and consistently low. After confirming that reagents and controls are acceptable, which of the following is the most probable cause for this systematic error?
- The sample concentration is too high.
- The instrument lamp is aging and has low light output. (Correct answer)
- Air bubbles are present in the cuvette.
- The wrong cuvette type (e.g., plastic instead of quartz) was used.
Correct answer: The instrument lamp is aging and has low light output.
In spectrophotometry, a failing or dim light source provides less incident light (I₀). This leads to a lower amount of light reaching the detector for all measurements, including the blank. When the instrument is zeroed with this low light level, subsequent sample measurements will appear to have lower absorbance values, resulting in falsely decreased calculated concentrations. This would affect all samples and controls systematically.
Medical Laboratory Technician Laboratory Operations and QC Questions and Answers
An MLT reviewing a Levey-Jennings chart for a daily glucose control run notices that the last two consecutive data points are outside the +2 SD limit.
Which Westgard rule has been violated?