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20 Cards in this Set

  • Front
  • Back
what are 3 general categories that medical tests can fall into?
quantitative: results are numerical; discrete units (ex: HR)
semi-quantitative: results are gradations (ex: reflexes)
binary: present,absent; yes, no; positive, negative
what are medical tests used for?
to test a hypothesis previously developed
do all tests test a hypothesis?
no, screening tests are done without a prior hypothesis being formed (ex: wellness screening)
also, history and physicals are done prior
what are three ways to form a hypothesis?
history (most important)
lab findings from screening
what are examples of tests in a history or physical?
history: standard questionnaires
physical: pulse, temp, reflex
what are some other categories of tests?
physiologic: electrical (EKG), functional (resp flow), measuring blood Q (angiography), stress test
clinical lab:
anatomic pathology: definitive test to confirm (autopsy)
what are 2 types of characteristics of a medical test?
analytical characteristics: DOING the test (what has to happen to get a valid result?); intrinsic to performance of a test

clinical use characteristics:interpreting the test result to diagnose/monitor
what are examples of analytical characteristics of a medical test?
reference range
analytical sensitivity
precision and accuracy
sources of error
cost and availability
reference range
SPECIFIC for test method, lab and geographic range
"normal" represents middle 95% of population
"normal" values don't exist-some ppl may lay outside the range and not be abnormal
what is the relationship between the number of test run and the number of expected "abnormal" results
directly proportional: more tests, more abnormal results
analytical sensitivity
required level of analyte to be detected
concentration v. amount
what are 3 main sources of error? which is the most common?
pre-analytical (99%!)
what are 3 factors that can influence preanalytical error?
specimen requirements
patient conditions
biological variability
what are some specimen requirements that, when not followed, could result in error? (4) what type of error?
(preanalytical error)
1. type of specimen (ex: venous v. arterial blood)
2. reagents added (ex: plasma v. serum- plasma req anticoagulants)
3. amount of specimen
4. conditions when obtaining, handling, transporting or storing the specimen.
what are patient factors/conditions that need to be considered when running a test? (5)
1. time of day-certain hormones fluctuate (cortisol?)
2. fasting (glucose)
3. standing v. supine (Ca2+ levels)
4. tourniquet time (pH)
5. exercise (incr m. enzymes)
how can biologic variability cause error in a test?
intra-individual: iron levels vary from day to day
inter-individual: IgM levels vary b/w indiv but not generally within an indiv
matters at decision point
analytical errors
made by the lab during testing
most labs have high precision (repeatablity); accuracy (knowing absolute true value of analyte) rarely known b/c usually dont have absolute standard to compare
what is required for accuracy of a test to be determined?
an absolute standard for the analyte
what is an example of a clinical lab test that can be both precise and accurate?
(standard set and maintained by US Bureau)
what are examples of how postanalytical errors occur?
(during interpretation of test results)
-use of inappropriate reference range
-interpreting a test outside its lifetime (ex: electrolyte levels useful within hours only)
-using 1 test when at least 2 are required to make judgement (cholesterol, glucose)
-thyroid testing??