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 Biological onset Early Diagnosis Possible Usual clinical diagnosis Outcome Recovery disability Death CP 1 CP 2 CP 3 T I M E Adapted from Clinical Epidemiology, Sacket, et. al.

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 Validity- sensitivity & specificity Sensitivity= A/A+C Specificity = D/D+B

Pay attention to Biases

And another bias… Length Bias

Screening recommendations Canadian Task Force US Task Force providers/guidelines- recommendations/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)iii 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

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; 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; Boyle P, Langman J S. ABC of colorectal cancer: Epidemiology. BMJ. 2000;321(7264):805–808

Colon Cancer Is there a “critical Period”?...a detectable asymptomatic phase during which therapy decreases morbidity or mortality? (and is superior to waiting till symptoms appear?) Colorectal cancer survival is highly dependent upon stage of disease at diagnosis, and typically ranges from a 90% 5-year survival rate for cancers detected at the localized stage; 70% for regional; to 10% for people diagnosed for distant metastatic 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, , with a special feature regarding survival. Cancer. 2004;101(1):3–27.

Colon Cancer Screening Is the test inexpensive? (monetary/ time) Is the test reproducible with low observer variability? Regular screening, beginning at age 50, is the key to preventing colorectal cancer. 1 The U.S. Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer using high- sensitivity fecal occult blood testing, sigmoidoscopy, or colonoscopy beginning at age 50 years and continuing until age 75 years. 1 1

Colon cancer CBS Harry Smith's Live Colonoscopy 07l0c48Rs

Colon cancer Is treatment acceptable and available?

Stage (TNM Staging Criteria) Standard Treatment Options Stage 0 Colon CancerSurgery Stage I Colon CancerSurgery Stage II Colon CancerSurgery Stage III Colon CancerSurgery Adjuvant chemotherapy Standard Treatment Options for Stages 0–III Colon Cancer

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