Download A discussion in clinical preventive medicine

Screening – a discussion in
clinical preventive medicine
Galit M Sacajiu MD MPH
What is Screening
The application of a test to a
presymptomatic individuals to
classify them with respect to
their likelihood of developing a
particular disease
Why to screen
 Decrease morbidity and mortality at
the individual level
 Decrease public health cost
 Decrease infectivity within a
population
 Personal wish for knowledge
What Diseases need to be
screened?
 Serious
 Availability of treatment
 Treatment before symptoms ensue
is more beneficial than after
disease manifested
 High prevalence
Early diagnosis and Natural
History of Disease
CP 1
CP 2
CP 3
Recovery
disability
Death
Biological
onset
Early
Diagnosis
Possible
Adapted from Clinical
Epidemiology, Sacket, et. al.
Usual
clinical
diagnosis
TIME
Outcome
Screening Tests
 Inexpensive
 Easy to administer
 Impose minimal discomfort
 Statistically sound:
Reliable
Valid
Reproducible
Statistically sound: Reliable &
Reproducible
The extent to which the
screening test will produce
the same or very similar
results each time it is
administered.
Statistically sound: Valid
Validity is the ability of a test to indicate which
individuals have the disease and which do
not. And it can be measured by sensitivity
and specificity
Sensitivity is the ability of the test to identify
correctly those who have the disease
Specificity is the ability of the test to identify
correctly those who do not have the disease
Calculate Validitysensitivity & specificity
Sensitivity= A/A+C
Specificity = D/D+B
Pay attention to Biases
And another bias…
Length Bias
Screening recommendations
 Canadian Task Force
http://canadiantaskforce.ca/fr/
 US Task Force
http://www.ahrq.gov/professionals/cliniciansproviders/guidelinesrecommendations/index.html
Examples
Chronic Disease - Hypertension
Infectious Disease – HIV
Malignancy – Colonoscopy
We recommend blood pressure measurement at all
appropriate primary care visitsi,ii). (Strong
recommendation; moderate quality evidence)
We recommend that blood pressure be measured
according to the current techniques described in the
Canadian Hypertension Education Program (CHEP)
recommendations for office and out-of-office
(ambulatory) blood pressure measurement). (Strong
recommendation; moderate quality evidence)
For people who are found to have an elevated blood
pressure during screening, the CHEP criteria for
assessment and diagnosis of hypertension should be
applied to determine whether the patient meets
diagnostic criteria for hypertension. (Strong
recommendation; moderate quality evidence)
Canadian Task Force
The HIV Screening. Standard Care.
program developed by the Centers for
Disease Control and Prevention (CDC)
gives primary care providers new tools to
help ensure all patients are tested for HIV
at least once in their life. Of the more than
1.1 million people in the United States
estimated to be living with HIV,
approximately 20% are unaware of their
HIV status.
Center for Disease Control and prevention
http://www.cdc.gov/actagainstaids/hssc/
Colon Cancer
 Is the condition Serious?
 Is its prevalence/incidence high enough?
Colorectal cancer is a major cause of morbidity and
mortality throughout the world. It accounts for over
9% of all cancer incidence. It is the third most
common cancer worldwide and the fourth most
common cause of death.
1. World Health Organization Cancer Incidence in Five Continents. Lyon: The World Health Organization and
The International Agency for Research on Cancer; 2002.
2. World Cancer Research Fund and American Institute for Cancer Research Food, Nutrition, Physical Activity,
and the Prevention of Cancer: A Global Perspective. Washington, DC: American Institute for Cancer Research;
2007.
3. Boyle P, Langman J S. ABC of colorectal cancer: Epidemiology. BMJ. 2000;321(7264):805–808
Colon Cancer
Is there cancer
a “critical
Period”?...a
Colorectal
survival
is highly
dependent
upon
stage of diseasephase
at
detectable
asymptomatic
diagnosis,
and
typically
ranges
from
a
90%
during which therapy decreases
5-year survival rate for cancers detected at
morbidity
mortality?
(and isto
the
localized or
stage;
70% for regional;
superior
to waiting
tillfor
symptoms
10%
for people
diagnosed
distant
metastatic
appear?)cancer. In general, the earlier
the stage at diagnosis, the higher the
chance of survival.
Jemal A, Clegg L X, Ward E, et al. Annual report to the nation on the status of cancer, 19752001, with a special feature regarding survival. Cancer. 2004;101(1):3–27.
Colon Cancer Screening
Regular screening, beginning at age
50,the
is the
to preventing
Is
testkey
inexpensive?
(monetary/
colorectal cancer.1 The U.S.
time)
Preventive Services Task Force
(USPSTF)
recommends
screening
Is
the test reproducible
with
low observer
for colorectal cancer using highvariability?
sensitivity fecal occult blood testing,
sigmoidoscopy, or colonoscopy
beginning at age 50 years and
continuing until age 75 years.1
Colon cancer
CBS
Harry Smith's Live Colonoscopy
http://www.youtube.com/watch?v=ku
07l0c48Rs
Colon cancer
Is treatment acceptable and
available?
Standard Treatment Options for Stages 0–III Colon Cancer
Stage (TNM Staging Criteria)
Standard Treatment Options
Stage 0 Colon Cancer
Surgery
Stage I Colon Cancer
Surgery
Stage II Colon Cancer
Surgery
Stage III Colon Cancer
Surgery
Adjuvant chemotherapy
Take Home Points
Is the condition Serious?
Is it common? Is its prevalence/incidence high
enough?
Is there a “critical Period”?...a detectable
asymptomatic phase during which therapy
decreases morbidity or mortality? (and is
superior to waiting till symptoms appear?)
Is treatment acceptable and available?
Is the test sensitive/specific?
Is the test inexpensive? (monetary/ time)
Is the test reproducible with low observer
variability?
Merci