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106 Cards in this Set
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Quality control |
It is a system of ensuring accuracy and precision in the laboratory by including quality control reagents in every series of measurements |
Done by testing known samples that resembles patient samples |
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Sensitivity |
It is the ability of an analytical method to measure the smallest amount of concentration of the analyte of interest |
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It is the ability of an analytical method to measure only the analyte of interest |
Specificity |
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Accuracy |
Nearness or closeness of the assayed value to the true value |
It can be estimated using 3 types of studies: 1.Recovery 2. Interference 3. Patient sample comparison |
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It is the ability of an analytical method to give repeated results on the the same sample that agree with one another |
Precision |
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Practicability |
Degree by which a method is easily repeated |
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Reliability |
Ability of a method to maintain accuracy and precision over an extended period of time during which equipment, reagent and personnel may change |
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Diagnositc sensitivity |
*It is the ability of an analytical method to detect the proportion of individuals with the disease
*indicates the ability of a test to generatre more true positive results and few false negative |
It is required in screening test |
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Diagnostic specificity |
*it is the ability of the analytical method to detect the proportion of individuals without the disease
*reflects the ability to detect true negative and few false positive |
It is required in confirmatory tests |
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Intralab quality control (Internal QC) |
*Involves analyses of control samples together with the patient samples
*important in daily monitoring of accuracy and precision |
Can detect both random and systematic errors in a daily basis |
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Interlab Quality Control |
*Involves proficiency testing programs that periodicaly provide samples of unknown concentrations to participating clinical laboratories *Important in maintaning long term accuracy of the analytical methods |
Used to determine state-of-the-art interlaboratory performance |
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College of American Pathologists (CAP) profiency program |
Gold standard for clinical laboratory external QC testing |
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Ensure clinicians that patient results are accurate |
Ultimate goal of proficiency testing |
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1. To check the stability of machines 2. To check the quality of reagents 3. To check technical errors |
Objectives of Quality Control |
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How many levels of control solutions is/are used in Genereal Chemistry Assays? |
2 levels |
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How many levels of control solutions is/are used in immunoassays? |
3 levels |
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To estabish statistical quality control on new instrument or on new lot number of controls, the different levels of control materials must be analyzed for how many days? |
20 days |
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Control limits are calculated using what measures? |
Mean and SD |
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Characteristics of an Ideal QC material |
1. Resembles human sample 2. Inexpensive 3. No communicable disease 4. No matrix effects 5. With known analyte concentrations 6. Convenient packaging |
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Alternative to human control materials |
Bovine control materials *not the choice for immunochemistry, dye-binding, and certain bilirubin assays |
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It is the result of improper product manufacturing, use of impurified human/nonhuman analyte addictives and altered protein compound |
Matrix effect |
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In evaluating analytical methods' accuracy and precision, how many samples should be run by each method in duplicate on the same day over 8-20 days, ideally within 4 hours? |
40-100 samples |
*if only 40 samples will be measured, daily analysis in duplicate of 2-5 specimens should be followed for at least 8 days |
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What is the most important characteristic of method evaluation? |
Determine if the total error (random and systematic error) is less than the allowable error (E⁴) |
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These are the errors encountered in the collection, preparation and measurement of samples. |
Variations |
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This type of error is present in all measurements; it is due to chance |
Random error |
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Identify whether it is caused by random or systematic error:
Intrument, operator, environmental conditions |
Random Error |
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Identify whether it is caused by random or systematic error: Inadequate reagent blank |
Systematic error |
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Identify whether it is caused by random or systematic error: Temperature fluctuations |
Random error |
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Identify whether it is caused by random or systematic error: Pipetting error |
Random error |
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Identify whether it is caused by random or systematic error:
Failing instrumentation |
Systematic error |
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Identify whether it is caused by random or systematic error: Mislabelling specimen |
Random error |
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Identify whether it is caused by random or systematic error: Deterioration of reagents |
Systematic error |
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Identify whether it is caused by random or systematic error: Poorly written procedures |
Systematic error |
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Identify whether it is caused by random or systematic error: Improper mixing of samples and reagents |
Random errors |
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Identify whether it is caused by random or systematic error: Unstable and inadequate reagent blanks |
Systematic error |
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An error that influences observations consistently in one direction (constant difference) |
Systematic error
*can be detected as either positive or negative bias |
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Exists when the difference between the test method and the comparative method values is proportional to the analyte concentration |
Proportional/slope/percent error |
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Difference between a target value and the assayed value |
Constant error *independent of sample concentration |
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The use of handwritten labels and request forms are the most common examples of this kind of error |
Clerical error |
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Pre-analytical errors |
1. Improper patient preparations 2. mislabelled specimen 3. Incorrect order of draw 4. Incorrecr patient identification 5. Wrong specimen container |
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Post-analytical errors |
1. Unavailable or delayed laboratory results 2. Incomplete laboratory results 3. Wrong transcription of patient's data |
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What are the 5 indicators of analytic performance? |
1. Internal QC 2. Proficiency tresting 3. Accreditation 4. Quality Assurance monitoring 5. Laboratory utilization |
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What is the first step in method evaluation? |
Precision study (estimates random error) *2 controls are run twice a day in a 10-20 day period |
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What is the most accurate measure of performance that would affect the laboratory values a clinician might observe? |
Total imprecision analysis |
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What is the most error free means of requesting laboratory tests? |
Online computer input |
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It is based on the quantity of error that will negatively affect clinical decisions and is expressed either in measurement units of analyte (mmol/L) or percentage |
Allowable error (E4) *Total error < Allowable error |
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It is based on the quantity of error that will negatively affect clinical decisions and is expressed either in measurement units of analyte (mmol/L) or percentage |
Allowable error (E4) *Total error < Allowable error |
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What is the measure of central tendency that is associated with symmetrical or normal distribution? |
Mean |
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It is the most frequently used measure of variation and is a measure of the dispersion of values from the mean |
SD |
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What is the percentile expression of mean? |
CV (index of precision) |
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What is this measure of variability that represents the difference between each value and the average of the data? |
Variance (also called SD²) |
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What is used to compare means or SDs of two groups of data? |
Inferential statistics |
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It is the simplest expression of spread |
Range |
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What is used to determine whether there is statistically sigficant difference between the SDs of two groups of data |
F-test |
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What is used to determine whether there is statistically sigficant difference between the means of two groups of data |
T-test |
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What is the midpoint of a distribution? |
Median |
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It is used to describe data with two centers |
Mode (most frequent observation) |
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It is the difference between the value of a data point and the mean value dividee by the group's SD |
SD index |
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What are 2 examples of parametric tests? |
T-test and ANOVA |
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What are the 3 measures of spread or distribution? |
CV, SD and range |
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What is the acceptable range limit? |
95% confidence limit (= +/- 2SD |
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It describes the distribution of all values around the mean |
SD |
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It is used to analyze precision data to give estimates of the within-in run, between run & total imprecision |
ANOVA |
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What is used to allow laboratorians compare SDs with different units? |
CV *CV in analyzers described as having reproducible test results can be lower than 1% |
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What is used to observe values of control materials over time to determinw the reliability of the analytical method? |
Quality control chart |
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It focuses on the distribution of errors from the analytical method rather than the values from a healthy population |
Gaussian Curve (Bell curve shape)
*occurs when data set can be accuratelt described by the SD and mean *total area under the curve is 1.0 or 100% |
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What is the most commonly used QC chart in clinical laboratory? |
Shewhart Levey-Jennings Chart *easily detects random or systematic errors |
A graphic representation of the acceptable limits of variation in the results of an analytical method |
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What is the common method used when using CUSUM? |
V-mask |
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It calculates the difference between QC results and the target means and is able to identify consistent bias problems |
CUSUM |
*It is able to give the earliest indication of systematic errors and can be used with 13s *Slope > 45° (+/- 2.7SD) =RESULTS ARE OUT OF CONTROL |
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What chart is used to compare results obtained on a high and low control serum from different laboratories |
Youden/twin plot |
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this kind of error is formed by contrast ol values that either increase or decrease for six consecutive days |
Trend |
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What is the main cause of trend? |
deterioration of reagents |
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This type of error is formed by control values that distribute themselves on one side or either side of the mean for six consecutivel days. |
Shift |
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They are highly deviating values that are far from the main set of values |
Outliers |
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What type of chart recognize that the use of simple upper and lower control limits is not enough to identify analytical problems? |
Westgard Control Chart |
It is recommended that at least 40 samples and preferably 100 samplea be run by comparison-of-methods experiment |
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What is the term used by Westgard to indicate that the analytical process is out of control? |
Control rule |
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Ten consecutive results are on the same side of the target mean |
10x |
Systematic error |
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The last four consecutive contro results exceeed either mean +/- 1SD |
41s |
Systematic error |
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One control result exceedds the mean +/- 3SD |
13s |
Random error |
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The last 2 control results ( or 2 results from the same run) exceed either mean +/-1SD |
41s |
Systematic error |
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The range or difference between the highest and lowest contl rresult within an analytical run exceeds 4SD |
R4s |
Random error |
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A control value between 2s and 3s suggests? |
Potential problem |
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When the control value exceeeds 3s, what should be done by the medtech? |
Corrective actions |
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It is the set of control and patient specimens assayed, evaluated and reported together |
Analytical run |
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It is the difference between two consecutive measurements of the same analytes on the same individual |
Delta check |
Most commonly used patient based-QC technique |
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What are 5 common interferences in measuring analytes? |
1.Hemoglobin 2. Lipids 3. Bilirubin 4.Anticoagulants 5. Preservatives |
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It is the concentration rangw over which the measured concentration is equal to the actual concentration without modification of the method |
Linear Range/Dynamic Range |
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It helps detect sample contamination or dilution,inadequate sample volume, etc. |
Physiologic limit (absurd value) |
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It is a type of analytical testing performed outside the confirmed s of the central laboratory, usually by nonlaboratorian personnel |
Point of care testing (POCT) (decentralized testing) |
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It can be envisiined as a tripod witjh program development, assessment and monitoring, and quality improvement forming three legs |
Quality Assurance |
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It includes effective test request form, clear instructions for patient preparation and specimen handling, appropriate turn around time for specimen processing, testing and result reporting |
Quality Patient Care |
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This value depends on sensitivity, specificity and prevalence of the disease being tested |
Predictive value |
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What theory describes the relationship between posttest and pretest probability of disease or no disease based on sensitivity and specificity? |
Baye's theorem |
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It is the probability that a positive test indicates disease |
Positive predictive value |
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It is the proportion of persosns with a negative test who are truly without disease |
Negative predictive value |
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What is the term used to denote the probability that a negative test will indicate the absence of disease? |
Negative predictive value |
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It is a pair of medical decision points that extend the limits of test results for a certain healthy population |
Reference limit/reference interval/reference value |
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Factors to be considered when establishing referenxe intervals |
1.Age, gender, genetic and socioeconomic factors 2. Quantity of reference individuals 3. Inclusion and exclusioin criteria for the required reference population 4.Physiologic and environmental conditions of the reference individuals 5. Categorize the potential reference individuals based oin criteria set 6. The specimen collection procedure 7. Analytical method used |
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To derive reliable estimates of reference intervls, at least how many individuals should be tested in each age and gender categories? |
At least 120 individuals |
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It is a laboratory result rhat represent a life-threatening situation that sometims not readily identified |
Critical or panic value |
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It is transmitted via electromagnetic waves that are characterized by their frequency and wavelength |
Energy |
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What is the distance between two successive peaks? |
Wavelength |
Expressed in nanometer |
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What is the wavelength of visible spectrum? |
400-700nm |
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What is the wavelength of ultaviolet region? |
<400nm |
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What is the wavelength of infrared region? |
>700nm |
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What is the main cause of shift? |
Improer calibration of the instruments |
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