Ch?: Lab Testing Flashcards
What is mean?
Average value of a series of values.
What is median?
The middle number of a set of values.
What is mode?
Most frequent value of a set of data.
What is standard deviation?
Analysis of how tightly values are distributed around the mean.
Two standard deviations encompass what percentage of values?
95.5%
What is the coefficient of variation?
Standard deviation as a percentage of the mean
The smaller the CV, is the test more precise or less precise?
More precise
A low CV assay has a narrow or wide distribution curve?
Narrow
A high CV assay has a narrow or wide distribution curve?
Wide
What is the standard deviation index?
The difference in terms of the number of standard deviations from the overall mean.
What is SDI used to determine?
Difference between your test results and the overall average of all participating labs.
What is a good SDI value?
Plus or minus 1
What is the borderline SDI value?
Plus or minus 1-2
What is a bad SDI value?
Plus or minus 2+
If all of your tests run all positive in terms of SDI’s, what does this suggest?
Your method is on the high side and you have a positive bias.
What is the sensitivity of a lab test?
Capacity of a test to identify all individuals with disease.
Increasing sensitivity of a test may increase what?
False positive test results
Sensitivity only uses values of what patient populations?
Patients with disease
What is specificity of a lab test?
Capability of a test to identify all individuals without disease
Increasing specifity of a test may increase what?
Number of false negative results
Specificity is only used with what population of patients?
Patients without disease
What is the positive predictive value?
Probability that a positive test result represents disease in an individual.
PPV only uses what for data?
Those with positive test results (true positives and false positives)
NPV represents what?
Probability that a negative test result represents absence of disease in an indvidiual
NPV only uses what for data?
Negative results (true negative and false negative)
What is accuracy?
Ability of a testing method to give the right or correct result
What is precision?
Ability of a testing method to give the same result time after time, whether or not the result is accurate or not.
What is the most common method for determining normal ranges?
Reference group method
Describe reference group method.
Samples are collected from a normal, random group of healthy individuals and a test value for each individual is obtained. You then determine the value of ranges within 2 standard deviations.
What is prognosis/treatment-derived normal range?
Use recommendations based on research and clinical experience to establish desired values.
Prognosis/treatment-derived range include what tests? 2
Cholesterol
Hypertension
When are threshold values used for normal ranges? (3)
Cardiac markers CK-MB, cTnI, and cTnT
Cardiac injury is presumed when what happens?
The threshold values are exceeded.
Is a Gaussian curve useful in threshold values?
No
What is the therapeutic drug reference range?
Therapeutic window for therapeutic drug levels.
What establishes the therapeutic drug reference range?
Experimentation and clinical data to maximize the drug’s therapeutic effects while minimizing the drug’s toxic effects.
What is comparison of previous test results and how is it used for determining normal range?
Patient’s previous test results are used as a basis to determine presence of disease or change in disease status.
Comparison of previous test results in used with what markers?
PSA, CEA, and CBC
What were once the work horses of medical laboratories?
Spectrophotometric or colorimetric assays
What are the steps of a spectrophotometric assay? 3
- Take patient’s serum and add a sample to the assay.
- Add a couple of reagents
- Observe for color change
What does nephelometry look for?
Cloudiness of a sample
What are the steps of nephelometry? 3
- Antigen of interest in a patient’s specimen is added
- Monoclonal antibodies against antigen are added
- Scattered light is measured.
What does it mean if nephelometry results in high level of scattered light?
High level of antigen
What are steps of enzyme immunoassay (ELISA)? 3
- Patient’s serum with antibodies is added to ligand coated well
- Enzyme conjugated anti human Ab’s are added which bind to the sample Ab’s.
- Enzymes form a substrate which can be measured by amount of light scattering