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Preventive Health Care Screening. Miriam Rabkin, MD. Preventive Health Care Screening. Screening basics: clinical epidemiology Screening guidelines Cancer screening: some examples. Screening Basics. What does “screening” mean? What do we screen for? risk factors for disease

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Preventive health care screening1
Preventive Health Care Screening

  • Screening basics:clinical epidemiology

  • Screening guidelines

  • Cancer screening: some examples


Screening basics
Screening Basics

  • What does “screening” mean?

  • What do we screen for?

    • risk factors for disease

    • presence of disease

  • What makes a disease or risk factor an appropriate target for screening?

  • What makes a test a good screening test?


Screening basics1
Screening Basics

does more screening =

better health care?


Characteristics of disease
Characteristics of Disease

  • Serious

  • Treatable

  • Pre-clinical detectable period

  • Early treatment is better than late

  • Prevalent


Characteristics of disease1
Characteristics of Disease

  • Why do we screen for serious disease?

    • why don’t we screen for varicose veins?

  • Why do we screen for treatable disease?

    • why don’t we screen for pancreatic cancer?


Characteristics of disease2
Characteristics of Disease

  • Why do we screen for diseases with a pre-clinical detectable period?

    • Ex: HIV vs. Legionella

  • Why do we screen for diseases where early treatment is better than late?

    • Ex: lung cancer


Characteristics of disease3
Characteristics of Disease

  • Why do we screen for prevalent disease?

    • More bang for the buck

    • Prevalence affects predictive value

      • predictive value depends not only on sensitivity and specificity but on prevalence

      • PPV = the chance of having the disease in the presence of a positive test

      • NPV = the chance of not having the disease in the presence of a negative test


Characteristics of disease4
Characteristics of Disease

  • The more prevalent a condition, the fewer false positive tests there will be

  • The less prevalent a condition, the fewer false negative tests there will be

  • No matter how good the test is!


Why do we test for prevalent diseases
Why do we test for prevalent diseases?

Although the combination ELISA/Western Blot test for HIV has extremely high sensitivity and specificity, predictive value is dependent on prevalence.

High risk population: prevalence = 40%

PPV = 0.985 NPV = 0.993

Low risk population: prevalence = 0.01% PPV = 0.0098 NPV = 0.999


Characteristics of test
Characteristics of Test

  • sensitive/specific

  • low-risk

  • “tolerable”

  • low-expense


Screening basics2
Screening Basics

  • Volunteer bias

  • Lead-time bias

  • Length bias


Volunteer bias
Volunteer Bias

  • Volunteers are different (“the volunteer effect”)

    • more health conscious?

    • more preventive health care?

    • more risk factors?

  • Volunteers tend to be healthier and to have lower rates of morbidity and mortality, no matter what the hypothesis under study is


Length bias
Length Bias

  • Diseases are heterogeneous

  • A screening test finds prevalent cases, not incident cases

  • Prevalence = incidence x duration

  • Cases with longer duration are, therefore, more likely to be detected by a screening test


Length bias1
Length Bias

Screening maneuver:


Length bias2
Length Bias

Length bias is the preferential detection of slowly progressive disease


Lead time bias
Lead Time Bias

  • Identifying a disease in its preclinical detectable period can artificially create the impression that screened populations do better than unscreened

  • can “phase-shift” the disease


Lead time bias1
Lead Time Bias

screen-detectable

clinically evident

death

5 years

clinically evident

death

2 years


Lead time bias2
Lead Time Bias

  • Because of lead-time bias, it is necessary to look at disease-specific and age-specific death rates in screened and unscreened groups when assessing a screening intervention.

  • Time from diagnosis to death does not tell you if a screening test is effective


Preventive health care screening2
Preventive Health Care Screening

  • Screening basics:clinical epidemiology

  • Screening guidelines

  • Cancer screening: some examples


Screening guidelines
Screening Guidelines

  • Whose guidelines?

  • Based on what sort of data?

  • How strict are the criteria?

  • What are the goals?


Screening guidelines1
Screening Guidelines

  • Who publishes guidelines?

    • The US Preventive Services Task Force

    • The American Medical Association, the American Cancer Society, the National Cancer Institute

    • Subspecialty organizations (AGA, AAFP etc.)

    • Health maintenance organizations

    • Patient advocacy organizations


Hierarchy of evidence
Hierarchy of Evidence

  • Randomized controlled trials

  • Nonrandomized controlled trials

  • Cohort studies

  • Case control studies

  • Comparisons between times and places

  • Uncontrolled experiments

  • Descriptive studies

  • Expert opinion


Strength of recommendations
Strength of Recommendations

A: good evidence to support the recommendation that the condition be considered in a periodic health exam

B: fair evidence to support the recommendation

C: insufficient evidence to recommend for or against

D: fair evidence to recommend exclusion

E: good evidence to recommend exclusion


Preventive health care screening3
Preventive Health Care Screening

  • Screening basics:clinical epidemiology

  • Screening guidelines

  • Cancer screening: some examples


Screening for cervical cancer
Screening for Cervical Cancer

  • Prevalent

  • Serious

  • Preclinical detectable period

  • Treatable

  • Early treatment is better than late


Papanicolaou testing
Papanicolaou testing

  • Papanicolaou testing is not sensitive but quite specific

  • There are no randomized trials of cervical cancer screening

  • Estimates are that triennial screening in women ages 20-64 reduces the cumulative incidence of cervical cancer by 91% and yields 96 cases for every 100,000 tests


Screening for cervical cancer1
Screening for Cervical Cancer

A: routine Pap smears for all women who have ever been sexually active and who have a cervix

B: frequency - at least every three years

There is little evidence that more frequent screening is beneficial (except in HIV-infected patients). May be effective in HPV-infected patients.

C: discontinue Pap smears at age 65 if patient has had regular normal Paps in past

C: HPV infection screening


Screening for colorectal cancer
Screening for Colorectal Cancer

  • Prevalent

  • Serious

  • Preclinical detectable period

  • Treatable

  • Early treatment is better than late


Screening for colorectal cancer1
Screening for Colorectal Cancer

Case for screening with annual DRE (digital rectal exam):

None. There is no evidence to support this screening strategy.


Screening for colorectal cancer2
Screening for Colorectal Cancer

Case for screening with FOBT (fecal occult blood testing):

  • Mandel et al. 1993 randomized 46,551 patients from 50-80 to FOBT screening every year, every two years, or control. Patients with positive FOBT underwent colonoscopy

  • After 13 years of follow-up, the age-adjusted mortality rate from colon cancer was 33% lower than in the annual testing group


Screening for colorectal cancer3
Screening for Colorectal Cancer

  • Subsequent randomized trials have duplicated this result and this screening maneuver (FOBT) is universally recommended

  • Annual FOBT is better than biennial screening

    • Byers et al. 1997: 33% reduction in mortality with annual FOBT, no reduction with biennial

    • Hardcastle et al. 1998: only 18% reduction with biennial FOBT


Screening for colorectal cancer4
Screening for Colorectal Cancer

Case for screening with sigmoidoscopy:

> No randomized trials !

> Selby et al. 1992: case-control study of rigid sigmoidoscopy screening. Odds ratio for dying of distal colorectal cancer was 0.41 (0.25-0.69) for those screened. No protective effect on dying of proximal colorectal cancer.


Screening for colorectal cancer5
Screening for Colorectal Cancer

  • Muller and Sonnenberg 1995: Case-control study of 32,702 veterans showed that endoscopic procedures of the large bowel (colonoscopy or sigmoidoscopy) reduced the risk of developing colorectal cancer by 50%


Screening for colorectal cancer6
Screening for Colorectal Cancer

  • Case for screening with colonoscopy:

    NB: There are no studies evaluating whether screening colonoscopy alone reduces the incidence or mortality of CRC in patients at average risk.


Screening for colorectal cancer7
Screening for Colorectal Cancer

  • Case for screening with colonoscopy:

    • colonoscopy was an integral part of RCTs of fecal occult blood testing

    • sensitivity of sigmoidoscopy (compared to colonoscopy as gold standard) was 44% in a 1991 study

    • “polyp science”

    • “expert opinion”


Screening for colorectal cancer8
Screening for Colorectal Cancer

  • Rex et al. 1997: Two consecutive same-day colonoscopies were performed in 183 patients showing miss rates of:

    • 6% for adenomas > 1 cm

    • 13% for adenomas 6-9 mm

    • 27% for adenomas < 5mm

  • Complication rates (and cost) of colonoscopy are significantly higher than those of sigmoidoscopy


Screening for colorectal cancer9
Screening for Colorectal Cancer

B: For all normal risk persons age > 50

1) annual FOBT (with colonoscopy if + )

2) flexible sigmoidoscopy every 3-5 years

C: DRE, BE, routine colonoscopy


Screening for ovarian cancer
Screening for Ovarian Cancer

  • Prevalent

  • Serious

    Preclinical detectable period?

  • Treatable

  • Early treatment is better than late


Screening for ovarian cancer1
Screening for Ovarian Cancer

  • transvaginal ultrasound has low yield

    • 5,678 volunteers age > 45 with a prior history of breast or gyn malignancy screened with TVUS

    • 2 stage I ovarian cancers were were found

  • screening 100,000 women would produce

    • 40 ovarian cancers

    • 5,398 false positives

    • 160 complications of laparoscopy


Screening for ovarian cancer2
Screening for Ovarian Cancer

  • Serum tumor markers (CA-125, NB/70K, TAG 72.3, CA 15-3) have limited specificity

  • screening studies have not yet been done in asymptomatic women


Screening for ovarian cancer3
Screening for Ovarian Cancer

D: routine screening with ultrasound or serum tumor markers is not recommended

C: there is insufficient evidence to recommend for or against screening women at increased risk


Screening for breast cancer
Screening for Breast Cancer

  • Prevalent

  • Serious

  • Preclinical detectable period

  • Treatable

  • Early treatment is better than late


Screening for breast cancer1
Screening for Breast Cancer

  • Self breast exam (SBE)

  • Clinical breast exam (CBE)

  • Mammography


Screening for breast cancer2
Screening for Breast Cancer

  • Self breast exam

    • widely taught

    • has benefits other than screening (education, empowerment)

    • evidence to support its use is weak

      • poor sensitivity and specificity

      • interim results from a very large RCT in China (267,040 women) show no difference in number, stage or size of breast cancers diagnosed or in mortality (after 5 years of follow-up)


Screening for breast cancer3
Screening for Breast Cancer

  • Clinical breast exam

    • higher sensitivity than SBE (87% detection rate for masses > 1 cm using a standardized model)

    • in randomized studies of breast cancer screening, a small percentage of cancers not seen by mammography are detected by CBE

    • mammography provides a substantial advantage over CBE alone


Screening for breast cancer4
Screening for Breast Cancer

  • Mammography

    • multiple trials in women aged 50-74 demonstrate a significant reduction in age-adjusted mortality with periodic mammography and all public health organizations support this strategy

    • data suggest but do not prove a benefit to more frequent mammography (every 12-18 months vs. every 24 months)


Screening for breast cancer5
Screening for Breast Cancer

  • Mammography - when to start?

    • 1993 NCI “there is insufficient evidence to make an informed decision regarding efficacy of screening as measured by reduction in breast cancer mortality in women aged 40-49 years.”

    • 1/97 NIH Consensus Development Conference “the data currently available do not warrant a universal recommendation for mammography for all women in their forties…”


Screening for breast cancer6
Screening for Breast Cancer

  • There have been 8 randomized controlled trials of screening mammography

    • none were designed to answer this question

    • meta-analyses show no reduction in mortality in women 40-49 after 7-9 years of follow-up

    • would there be a mortality benefit after 10-15 years of follow-up? (remember, then the women would be in their 50s and 60s and would be screened anyway)


Screening for breast cancer7
Screening for Breast Cancer

  • Kerlikowske et al. JAMA 1995

    meta-analysis of 13 studies (the 8 RCTs and 5 case-control studies)

    RR for breast cancer mortality

    women 50-74 0.74 (0.66 - 0.83)

    women 40-49 0.93 (0.76 - 1.13)

    7-9 years of follow-up 1.02 (0.82 - 1.27)

    10-12 years 0.83 (0.65 - 1.06)


Screening for breast cancer8
Screening for Breast Cancer

  • Mammography - when to stop?

    • None of the mammography trials included women over the age of 75

    • Most groups recommend continued screening for older women in good health (with reasonable life expectancies)


Screening for breast cancer9
Screening for Breast Cancer

  • Mammography - what interval?

    • Again, no trial designed to answer this question

    • No major differences in outcome when you compare trials of annual mammography to trials of biannual mammography

    • Subgroup analysis suggests benefit from more frequent mammography - ? every 18 months

    • The more mammograms you perform, the more false positive results you will incur


Screening for breast cancer10
Screening for Breast Cancer

  • Mammography between 40-49 at the discretion of patient and provider

  • Annual or biannual mammography between the ages of 50-74

  • Mammography after the age of 74 at the discretion of patient and provider


Screening for breast cancer11
Screening for Breast Cancer

  • Incomplete or unconvincing data should not cause intellectual paralysis!

  • Cannot be dogmatic in areas where decision appears to be a “toss-up”

  • Health care providers must actively solicit informed patient preferences


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