Screening, Testing And Clinical Decision Making Flashcards
Primary prevention
Prevention of disease in those who do not yet have it
-immunization, diet, exercise, sun protection, public policies, purifying water supply, health fairs, counseling
Secondary prevention
Identification of those who have the disease but not yet developed signs and symptoms
- shorten its life span, or if no curs, increase quality of life
- cholesterol, prostate, breast exams, SCREENING PROGRAMS
Tertiary prevention
Prevention of complications in those with the signs and symptoms
- reduce disability
- rehabilitations, PT, respiratory therapy
Screening programs are considered _____ prevention
Secondary
Characteristics of a good screening test
Easy to perform, quick, inexpensive, safe
The probability of cases of a condition accurately identified by the screening test
Yield
-E.g. to detect 1 case of glaucoma, 100 must be screened
Ability of a test to distinguish between those who have the disease and those who dont
Internal validity (accuracy)
Generalizability
External validity
Repeatability
Reliability
-OHTS study-86% of first time abnormal fields were normal on second tests
The abiltiy of a test to correctly identify people with a disease
Sensitivity
Sensitivity proportions
# of people with the disease who testpositive/# of people with the disease who are tested -positive/all diseased who are tested
TP/TP+FN
Ability of a test to correctly identify people without a disease
Specificity
Specificity proportions
TN/TN+FP
Number of people without the disease who test negative/number of people without the disease who are tested
4 possible outcomes for specificity and sensitivity
True positive
False positive
True negative
False negative
Screening for glaucoma at a health fair
- screen 100 persons with icare tonometer and FDT matrix VF
- criteria for failure-IOP >21 and VF defect
- all 100 will later have complete eye exams at the clinic determine whether or not they truly have glaucoma-“gold standard”
What is the sensitivity and specificity: test glaucoma-20 true glaucoma, 10 true normal; test normal-5 true glaucoma, 65 true normal.
Sensitivity
20/25=80%
Specificity
65/75=87%
False negative
5/(5+20)=1-0.8 (sensitivity)
20%
False positive
10/(10+65)=1-0.87 (specificity)
13%
Tests with both high sensitivity and specificity
It is difficult to find a test with both-there is often a trade off between the two
A test with poor sensitivity
Many false negatives
-many people with the disease will pass the test
A test with poor specificity
Many false positives
-many people without the disease will fail the test
Emphasize sensitivity to minimize
False negatives
- when there is a big penalty for missing the diagnosis
- dangerous but tredaqtable conditions-HIV, syphilis, TB, brain tumors
- when you are more suspicious of the disease (e.g. higher prevalence)
Emphasize specificity to minimize ______
False positive
- when treatment involves risk and costs. Before subjecting patients to chemo, tissue diagnosis (highly specific test) is required.
- when you are less suspicious of the disease. E.g. lower prevalence
Choosing between sensitivity and specificity: confrontation visual fields
- higher specificity (if you’re normal, tour more likely to pass this test than a Humphrey visual field)
- low sensitivity (patients with subtle field defects will not be identified because targets are easily seen)
- good for general population
Choosing between sensitivity and specificity: automated threshold visual fields
- lower specificity-many normals will give abnormal results t first, due to learning curve
- much higher sensitivity
- use when there is a higher suspicion for glaucoma
- do not use indiscriminately because of the time and costs of repeating “abnormal” fields on normal eyes
How do we decide whether a test result is normal or abnormal
Cutoff points are chosen on a continuum between normal and abnormal
-want the test to be sensitive enough to diagnose disease but specific enough not to subject patients to unnecessary treatment
