Lecture 11b - Quality Part 2 Flashcards
Define sensitivity
The proportion of cases HAVING a specific disease or condition that gives a POSITIVE test result.
Define specificity
The proportion of cases with ABSENCE of a specific disease or condition that gives a NEGATIVE test result.
Define true positive
Positive test result and have the disease
Define true negative
Negative test result and do not have the disease
Define false positive
Positive test result but do not have the disease
Define false negative
Negative test result but does have the disease
How is sensitivity measured?
It measured how much of a given substance is measured.
The more sensitive the test = the smaller the amount of assayed substance that is measured (detected)
How do we find percent sensitivity?
Define predictive value.
The ability to predict the results of an analysis of the same data by using another test instrument or measurement; contributes to the validity of a test.
How do we determine positive predictive value?
How do we determine negative predictive value?
Define mean
Mathematical average taken by adding up all of the values in a data set and then dividing the total by the number of results in the data set.
Define median
Middle value of a body of data
Define mode
The value most frequently occurring in a body of data.
Define standard deviation (s or SD)
A measure of the spread, or variability, in a data set.
Define variance
The precision of a group of numbers
Define coefficient of variation (CV)
Calculates the SD as a “percent of the mean”.
Can be used to compare SDs of two samples.
How would a lab determine a control range?
- Run an aliquot of control sample daily for 15-25 days
- Treat exactly like a patient
- Calculate the mean
- Calculate the variation from the mean using SD
- +/- 2SD
What is a Levy Jennings chart?
A statistical chart used to measure changes in quality control values.
What is a shift in QC?
A sudden and sustained change in one direction in control sample values.
Causes - a sudden malfunction with an instrument, QC contamination, etc.
What is a trend (or drift) in QC?
A gradual change in the control sample results; control value directions moves progressively in one direction from the mean for at least three days.
Causes - deterioration of reagents, instrumentation, or the control sample.
What is a dispersion in QC?
When a random error or lack of precision increases.
Causes - instability problems with instrumentation.
Define as a shift, trend, or dispersion.
Shift
Define as a shift, trend, or dispersion.
Trend
Define as a shift, trend, or dispersion.
Dispersion
What are Westgard Rules?
Rules formulated to analyze data in control charts based on statistical methods.
When is a 1-2S violated?
Violated when one of two control results falls outside of 2SD.
Warning rule; specimens not rejected.
When is a 1-3S violated?
Violated when any QC result falls outside of 3 SD.
When is a 2-2S violated?
Violated when two consecutive control values for the same level fall outside of 2 SD in the same direction, or when both control levels in the same test batch exceed 2 SD.
Patient results cannot be reported.
When is a 3-1S violated?
Violated when 3 consecutive control results are greater than 1 SD and on the same side of the mean.
Indicates systematic bias.
When is a 4-1S violated?
Violated when four consecutive control results are greater than 1 SD on the same side of the mean.
Indicates systematic bias.
When is a R-4S violated?
Violated when one control measurement exceeds the +2 SD and the other exceeds the -2 SD control limit.
Patient results cannot be reported.
When is Nx violated?
Violated when 7, 8, 9, 10, or 12 control results are on the same side of the mean.
Indicates systematic error.
When is 10x violated?
Violated when 10 consecutive QC results for one level of assay control are on one side of the mean OR both levels of control have five consecutive results that are on the same side of the mean.
Patient results cannot be reported.
What QC rules are being violated?
1-2S and 1-3S
What QC rules are being violated?
2-2S and 3-1S
What QC rules are being violated?
4-1S and R-4S
What QC rules are being violated?
Nx and 10x
What are some nonanalytical factors for quality assessment?
Qualified personnel, established laboratory policies and procedure manual, test requisitioning, patient identification and specimen labeling, specimen transportation and processing, preventative maintenance of equipment.
What must a test requisition include?
- Patient ID information
- Time and date of specimen collection
- Source of specimen
- Analyses to be performed
How many patient identifiers are needed prior to specimen collection? What are they?
Two; these include:
- First and last name
- Date of birth
- Medical Record Number (MRN)
How quickly should a test be performed to ensure accurate results?
2 hours
Define turn around time (TAT)
The amount of time in which the test should be completed (determined by laboratory).
