Laboratory Operations and QC Flashcards
6 cards from real Medical Laboratory Technician Exam practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Laboratory Operations and QC flashcards as text
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?
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.
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?
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.
To find comprehensive information regarding the hazards, safe handling, and emergency procedures for a new chemical reagent, an MLT should primarily consult the:
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.
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)?
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%.
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?
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.
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?
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.