Intro to Diagnostic Interpretation

Question 1

Accuracy

Answer 1

• ability of test to give correct answer
• agreement of the test result w/ pt true condition is best measure of accuracy

Question 2

True positive

Answer 2

• disease is present and pt tests positive for it

Question 3

false positive

Answer 3

• disease is absent
• pt tests positive for it

Question 4

true negative

Answer 4

• disease is absent
• pt tests negative for it

Question 5

false negative

Answer 5

• disease is present
• pt tests negative for it

Question 6

sensitivity

Answer 6

• ability to detect if a dz is present
• in tests w/ high sensitivity, large portion of ppl w/ dz will test positive
• good at picking up the abnormality in person w/ dz
• few false negative
• sensitivity = true positives/ ((true positives + false negatives)
  • expressed as %
• When the Sensitivity of a test is high, a Negative response rules OUT the target disorder “SnNOUT”

Question 7

specificity

Answer 7

• ability to exclude persons who to not have dz
• high specificity= large portion of ppl w/out dz will test negative for the dz
• if good, will have few false positives
• true negatives/(true negatives+ false positives)
  
  • expressed in %
• •When the Specificity of a test is high, a Postive response rules IN the target disorder “SpPIN”

Question 8

incidence

Answer 8

• # of new cases that have occured in a specific time interval divided by pop. at risk over that time period

Question 9

prevalence

Answer 9

• refers to the # of ppl w/ a given dz (new cases and those who got the dz in past and are still surviving) at a given point in time divided by the population at risk at that point in time

Question 10

positive predictive value

Answer 10

• proportion of pt w/ a positive test who have the dz
• tells you how often a positive test represents a true positive
• true positives/(true positives + false positives)

Question 11

negative predictive value

Answer 11

• proportion of pt w/ a negative test that do not have the dz
• tells you how often a negative test represents a true negative
• true negatives/ (true negatives + false negatives)

Question 12

screening test

Answer 12

• testing for a dz in an individual that appears healthy (i.e. has no symptoms or signs of the dz in question)
• Universal (or population) screening refers to the screening of every individual within a population
• Selective (targeted or risk-based) refers to screening of individuals in which there is reason to believe that the prevalence of the dz is higher

Question 13

diagnostic test

Answer 13

• diagnostic testing is done in pts who have symptoms or signs of a dz
• To establish a diagnosis
• To provide prognostic information
• To monitor ongoing therapy

Question 14

what does a reference range represent?

Answer 14

• Normal ranges for lab tests based upon population studies
• “Normal” is usually defined as those test values that fall within 2 standard deviations of the mean, which includes 95% of all results
• By definition, 5% of healthy population will have an abnormal test - slightly abnormal tests should be interpreted clinically for their (usually lack of) significance!

Question 15

why are there variations in interpreting lab test?

Answer 15

• A test may have a single normal range, or there may be different normal ranges based on age, gender, race, or other factors
• Ranges vary slightly between labs depending on methodologies / equipment used

Question 16

critical value

Answer 16

• a test result that conveys potentially life-threatening information and is defined for “out of range” test results that must be acted upon as soon as possible

Question 17

what are the implications associated with critical value?

Answer 17

• A critical value has life-threatening, time-dependent implications and must be directly reported to the health care provider for immediate action