Epidemiology 503
Screening: Multiple Testing
How do multiple tests improve
screening programs?
Carrie Karvonen-Gutierrez, PhD, MPH
Learning Objectives & Key Concepts

Describe the two types of
multiple testing screening
protocols

Calculate net sensitivity and
net specificity when using
sequential testing

Key Terms:


Sequential testing
Simultaneous testing
Evaluate the usefulness of
multiple screening tests on
net sensitivity & net
specificity
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Using Multiple Tests

Sequential Tests (2-stage):



Simultaneous Tests (parallel):



Less expensive, less invasive, less uncomfortable test first
If positive on first test, then follow-up with additional testing
Conduct multiple screening tests at the same time
To be considered positive, the person can test positive on
either test. To be considered negative, the person must test
negative on all tests
Each test has own sensitivity and specificity, so must
calculate net sensitivity and net specificity
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Sequential Cervical Cancer Screening


Visual Examination and Pap Smear (Denny et al. Am J Obstet Gynecol 183;383-8, 2000.)
Prevalence 0.5% (500/100,000 women)
1: Visual Exam
Sensitivity=75%
Specificity=81%
Cervical Cancer
No Cervical
Cancer
TOTAL
TOTAL
500
99,500
100,000
2: Pap Smear
Sensitivity=82%
Specificity=93%
Cervical Cancer
No Cervical
Cancer
TOTAL
375
18,905
19,280
Positive
Negative
Positive
Negative
TOTAL
4
Sequential Cervical Cancer Screening
1: Visual Exam
2: Pap Smear
Cervical Cancer
No Cervical Cancer
Cervical Cancer
No Cervical Cancer
Positive
375
18,905
308
1,323
Negative
125
80,595
67
17,582
TOTAL
500
99,500
375
18,905
NET Sensitivity = # diseased who screen positive / # with disease
NET Specificity = # nondiseased who screen negative / # without disease
Sequential testing:
↓ net sensitivity
↑ net specificity
Sensitivity
Specificity
Visual Exam
75%
81%
Pap Smear
82%
93%
Net
62%
99%
5
Simultaneous Screening

Screen using more than 1 test at same time

Each test has its own sensitivity and specificity

To be positive, can screen + on either test

To be negative, must screen – on ALL tests

Examples:


Clinical “work-up”
Urine screening for doping agents
Simultaneous testing:
↑ net sensitivity
↓ net specificity
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Sequential vs. Simultaneous Testing
Sequential Testing
Test 1
+
Test 2
+
Clinically
Positive
Clinically
Negative
↓ net sensitivity
↑ net specificity
-
Simultaneous Testing
Test 1
+
-
Clinically Positive
Clinically Negative
Clinically
Negative
Test 2
+
Clinically Positive
↑ net sensitivity
↓ net specificity
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Summary

Sequential testing is when an initial screening test is done,
and those individuals that screen positive are screened
again using a second test

Simultaneous testing is when multiple screening tests are
undertaken at the same time, on the same samples

Utilization of multiple testing can improve net sensitivity
(simultaneous testing) or net specificity (sequential testing)
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