Title Clinical Chemistry Review Booket Part 1 SY2024-2025.docx.pdf ✅

CLINICAL CHEMISTRY Quality Control ∙ A system to monitor the analytical process and to detect errors that can affect accuracy and precision PARAMETERS OF QUALITY CONTROL 1. Accuracy ∙ The closeness of the assayed value to the true value 2. Precision / Reproducibility ∙ The closeness of the assayed value to a repeated value 3. Sensitivity / Detection Limit ∙ The ability of an analytical method to measure the smallest concentration of the analyte of interest 4. Specificity ∙ The ability of an analytical method to measure only the analyte of interest 5. Diagnostic sensitivity ∙ The ability of an analytical method to detect the proportion of individuals with the disease ∙ The ability of the test to generate more true-positive results and fewer false-negative. SCREENING TEST require high sensitivity so that no case is missed 6. Diagnostic specificity ∙ The ability of an analytical method to detect the proportion of individuals without the disease ∙ The ability of the test to detect true-negative results and few false-positives. CONFIRMATORY TEST requires high specificity to be certain of the diagnosis 100% sensitivity and specificity indicate that the test or method detects every patient with the disease and that the test is negative for every patient without the disease. KINDS OF QUALITY CONTROL 1. Intralab Quality Control (Internal QC) ∙ Involves the analyses of control samples together with the patient specimens ∙ Important for the daily monitoring of accuracy and precision of analytical methods ∙ Detects both random and systematic errors in a daily basis
2. Interlab Quality Control (External QC) ∙ Involves proficiency testing programs that periodically provide samples of unknown concentrations to participating clinical laboratories ∙ Important for maintaining long-term accuracy of the analytical method SOLUTIONS FOR CHECKING ACCURACY AND PRECISION 1. Standard ∙ A material of known composition available in highly purified form ∙ Universal color: Colorless 2. Control ∙ Material with physical and chemical properties closely resembling the test specimen and containing pre analyzed concentrations of the substances being measured ∙ Universal color: Yellow SOURCES OF CONTROL 1. Human-based control ∙ Non-infectious, non-icteric and non hemolyzed 2. Bovine-based control ANALYTICAL ERRORS 1. Systematic Error ∙ Error that occurs predictably once a pattern of recognition has been established Causes: a. Deterioration of reagents and control materials b. Aging calibrators c. Poorly written procedures d. Wear and tear of instrument e. Improperly made standard solutions 2. Random Error / Indeterminate ∙ Error that occurs unpredictably ∙ Basis of imprecision which results in varying differences between repeated measurements Causes: a. Variation in handling techniques: pipetting, mixing and timing b. Mislabeling of samples c. Temperature fluctuations d. Calibrator reconstitution e. Sample evaporation
QUALITY CONTROL CHARTS 1. Gaussian Curve (Bell-Shaped Curve) ∙ It occurs when data elements are centered around the mean with most elements close to the mean ∙ Normal distribution curve: mean = median = mode +1SD – 68.27% +2SD – 95.45% +3SD – 99.73% 2. Cumulative Sum Graph ∙ It calculates the difference between QC results and the target means ∙ Common method: V mask ∙ It gives the earliest indication of systematic errors and can be used with the 13s rule 3. Youden/Twin Plot ∙ It is used to compare results obtained on a high and low control serum from different laboratories ∙ The points falling from a center but on the 45 O line suggest a proportional error, and points falling from the center but not on the 45 O line suggest a constant error. 4. Shewhart Levey-Jennings Chart / Dot Chart ∙ Most commonly used chart for QC recording ∙ Analyte concentrations are in the Y-axis; day and time are plotted in the X-axis Evaluation of LJ Chart a. Trend ∙ Gradual deviation formed by control values that either increase or decrease for six consecutive days ∙ Main cause: Deterioration of reagents b. Shift ∙ Sudden or abrupt change formed by control values that distribute themselves on one side or either side of the mean for six consecutive days ∙ Main cause: Improper calibration of the instrument c. Outliers ∙ Highly deviating values that are far from the main set of values 5. Westgard Control Chart ∙ Use of upper and lower control limits is not enough to identify analytical problems ∙ Sensitivity of the multirole procedure can be increased to detect smaller systematic errors by increasing the number of observations considered. Westgard QC Rules 12s Used as screening or warning rule when a single QC result falls outside +2SD 13S Single QC result falls outside +3SD R4S Two consecutive values differ by more than 4SD 22S Two consecutive QC results fall more than 2SD on the same side of the mean 41S Four consecutive QC results are more than 1SD away from the mean in the same direction
10x Ten consecutive QC results are on the same side of the target mean