Lab Testing: QC & Pre-Analytical Variables PDF
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This document covers pre-analytical variables and quality control (QC) in laboratory testing. It explains how factors like patient preparation and sample handling can impact results. It also introduces key concepts such as accuracy, precision, and sensitivity.
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Lec2 It seems like you’re diving deep into pre-analytical variables and QC terms, which are key to quality control in lab testing! Here’s a breakdown to reinforce what each section covers and how they relate to achieving accurate, reliable test results. Pre-analytical Variables These variables in...
Lec2 It seems like you’re diving deep into pre-analytical variables and QC terms, which are key to quality control in lab testing! Here’s a breakdown to reinforce what each section covers and how they relate to achieving accurate, reliable test results. Pre-analytical Variables These variables in uence lab test outcomes even before the actual analysis, often accounting for up to 75% of lab errors. Let’s go through a few main points: 1. Patient Identi cation: Ensuring the correct patient is tested is foundational to reliable results. 2. Patient Preparation: Factors like fasting or diurnal variations (e.g., cortisol levels) can signi cantly impact test results. 3. Site Selection and Preparation: Proper technique, including choosing and preparing the venipuncture site, minimizes contamination risks. 4. Tourniquet Application and Venipuncture Technique: Proper application time is key to avoiding hemolysis and ensuring sample quality. 5. Special Handling: Certain samples need special treatment (e.g., chilled transport for ammonia or lactic acid) to preserve stability and accuracy. 6. Sample Stability: Knowing the stability of whole blood, serum, and plasma at various temperatures prevents degradation and ensures accurate measurements. Key QC Terms in Laboratory Performance 1. Accuracy: Measures how close a test result is to the true value. Typically validated using assayed control samples with known values. Higher accuracy = results close to the target value. 2. Precision: Refers to consistency and reproducibility among multiple test results for the same sample. Intra-assay precision: Consistency within a single test run. Inter-assay precision: Consistency across multiple test runs. High precision reduces variability, improving reliability. 3. Speci city: Measures if a test solely identi es the intended analyte. Low speci city can result in false elevations due to interference (e.g., similar hormones like FSH, LH). Poor speci city decreases test accuracy. 4. Sensitivity: Indicates the test’s ability to detect small amounts of the analyte. Low sensitivity means the test may struggle with low concentrations, impacting accuracy and precision. Basic QC Statistics 1. Mean (Average): The average value of data points; often used to establish the “true value” in a sample set. 2. Standard Deviation (SD): Re ects how spread out the data points are from the mean; key to assessing precision. Low SD = high precision and lower variability. Laboratories usually accept values within 2 SD from the mean. 3. Coe cient of Variation (CV): The SD expressed as a percentage of the mean, allowing comparison across di erent concentrations. Lower CV = higher precision, crucial for reliable lab results. Study Tips: Use Visual Aids: Diagrams showing the pre-analytical steps can clarify processes like venipuncture technique or sample handling. Practice QC Calculations: Get comfortable calculating mean, SD, and CV, as these are central to lab QC. Scenario Practice: Consider hypothetical lab scenarios to apply your understanding of accuracy, precision, and error classi cations.
