why do we need lab data? Answer - * diagnostic and screening purposes
-discover disease, confirm suspected disorder, differentiate among different
diagnosis, detect reoccurance
* determine severity of disease
* measure efficacy and toxicity of treatment and guide course of therapy
invasive vs non-invasive lab test Answer - invasive: examine fluids and tissues
obtained by needle, tube, device or scope to penetrate or enter the body. there
is some risk
non-invasive test: Test does not require skin penetration or an intrustment
entering the body. minimal risk to patients
example of invasive lab tests vs example of non-invasive lab tests Answer -
invasive: blood draw from screen, lumbar puncture to take cerebral spinal fluid,
tumour biopsy
non-invasive: urine test for drug screen, BP, sweat chloride test for cystic
fibrousis
accuracy vs precision Answer - accuracy: extent to which the mean measure is
close to the true value
,precision: agreement of results when the test is run many times on the same
sample
explain what sensitivity is (in a test result interpretation). when are highly
sensitive tests desirable? Answer - ability of test to identify positive results in
patients who actually have the disease. True positive rate: % of patients with
the disease who actually test positive
highly sensitive tests are desirable to test for treatable, life threatening disease,
to avoid false negatives
SNOUT: SeNsitive test, Negative result is good for ruling OUT
what is specificity (test result interpretation)? what does it mean if test has
95% specificity? Answer - ability of test to identify negative results in patients
who do not have the disease. True negative rate: % of patients without the
disease who actually test negative.
95% specificity means there will be 95% true negative and 5% false positive
rate. (5% of people without the disease will be misidentified as having it)
SPIN: SPecific test, Positive result is good for ruling IN
formula for sensitivity vs formula for specificity Answer - sensitivity:
[TP/(TP+FN)] x100%
specificity: [TN / (FP+TN)] x100%
, what is sensitivity of an assay Answer - the range at which an assay can
accurately measure an analyte.
ie. lower limit of detection of an immunoassay is the lowest quantity of a
substance that can be distinguished from the absence of that substance. The
lower the LOD the higher the sensitivity.
what is specificity of an assay? Answer - degree of cross-reactivity of the
analyze with other substances, in other words, does the test analyze what you
are looking for or is there interference from other substances.
ie. low specificity for utine samples that test for barbiturates but could be
positive in patients who haven't even ingested barbituates but a similar
structure such as phenytoin.
what does predictive value asses? what is positive vs negative predictive value?
Answer - asses a test's reliability in that it considers sensitivity, specificity and
prevalence of the disease in the population.
positive predictive value: proportion of patients w positive test results who are
correctly diagnosed (who are actually positive)
negative predictive value: percent that are actually negative
what is a type 1 error/p value? Answer - false positive: test outcome is positive
when the person doesnt actually have the condition
the COVID test says positive but you dont actually have covid
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