Section 2.3: Preventive Medicine & Screening Guidelines

Preventive Medicine & Screening Guidelines

Preventive medicine is a major focus of the USMLE Step 3. The exam tests your ability to apply the United States Preventive Services Task Force (USPSTF) screening recommendations, CDC adult vaccination schedules, and the core principles of preventive health.

Levels of Prevention

Preventive measures are categorized into four distinct levels based on the stage of disease and the goal of the intervention:

• Primary Prevention: Aims to prevent the onset of disease by reducing exposure to hazards and promoting health. Examples include immunizations, smoking cessation counseling, routine exercise, and starting a statin for primary cardiovascular prevention in high-risk asymptomatic patients.
• Secondary Prevention: Focuses on the early detection and treatment of asymptomatic disease to arrest its progression. Examples include screening mammograms, Papanicolaou (Pap) smears, colonoscopy screening, and blood pressure screening.
• Tertiary Prevention: Focuses on managing established, symptomatic disease to minimize complications, prevent disability, and restore function. Examples include prescribing beta-blockers post-myocardial infarction to prevent remodeling, performing diabetic retinopathy screening, and physical therapy following a stroke.
• Quaternary Prevention: Set of activities that identifies patients at risk of over-medicalization, protects them from new medical invasions, and suggests ethically acceptable interventions. Examples include avoiding unnecessary diagnostic testing or imaging (e.g., avoiding imaging for uncomplicated low back pain).

USPSTF Screening Recommendations

The USPSTF provides evidence-based recommendations graded A, B, C, or D. Step 3 heavily tests Grade A and B recommendations.

Cancer Screening

• Breast Cancer: The USPSTF recommends biennial (every 2 years) screening mammography for women aged 40 to 74 years. This represents an important update from the previous recommendation to begin routine screening at age 50. Screening after age 74 is based on individual risk and life expectancy.
• Cervical Cancer: Screen women aged 21 to 65. From age 21 to 29, perform cervical cytology (Pap smear) alone every 3 years. From age 30 to 65, the options are: cytology alone every 3 years, high-risk human papillomavirus (hrHPV) testing alone every 5 years, or hrHPV and cytology co-testing every 5 years. Discontinue screening at age 65 if the patient has had adequate negative prior screening (3 consecutive negative cytology or 2 consecutive negative hrHPV/co-tests within the last 10 years, with the most recent test within 5 years) and is not at high risk. Do not screen patients who have had a total hysterectomy with removal of the cervix and no history of high-grade precancerous lesions (CIN 2 or 3) or cervical cancer.
• Colorectal Cancer: Screen adults aged 45 to 75. Screening options include: colonoscopy every 10 years, fecal immunochemical test (FIT) annually, guaiac-based fecal occult blood test (gFOBT) annually, multi-target stool DNA testing (FIT-DNA/Cologuard) every 1 to 3 years, CT colonography every 5 years, or flexible sigmoidoscopy every 5 years. Screening in adults aged 76 to 85 should be individualized based on overall health and screening history.
• Lung Cancer: Recommend annual screening with low-dose computed tomography (LDCT) in adults aged 50 to 80 who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years. Discontinue screening once a person has not smoked for 15 years, develops a health problem that substantially limits life expectancy, or is unable or unwilling to undergo curative lung surgery.

Cardiovascular and Metabolic Screening

• Abdominal Aortic Aneurysm (AAA): Perform a one-time screening for AAA with abdominal duplex ultrasound in men aged 65 to 75 who have ever smoked (defined as smoking at least 100 cigarettes in their lifetime). The USPSTF recommends shared decision-making for non-smoking men in this age group and recommends against screening in women.
• Hypertension: Screen all adults aged 18 or older. Crucial Step 3 point: Confirm elevated office blood pressure measurements with out-of-office measurements (ambulatory blood pressure monitoring or home blood pressure monitoring) before establishing a diagnosis of hypertension and initiating pharmacotherapy, unless the patient presents with hypertensive emergency or severe elevations (e.g., $\ge 180/120$ mmHg).
• Type 2 Diabetes Mellitus: Screen for prediabetes and type 2 diabetes in asymptomatic adults aged 35 to 70 who are overweight or obese (BMI $\ge 25$ kg/m², or $\ge 23$ kg/m² for Asian Americans). Screening methods include fasting plasma glucose, HbA1c, or a 2-hour oral glucose tolerance test. Repeat testing every 3 years if results are normal.
• Lipid Disorders & Cardiovascular Risk: Screen adults aged 40 to 74 with the pooled cohort equations to calculate 10-year atherosclerotic cardiovascular disease (ASCVD) risk. Initiate a low-to-moderate dose statin for primary prevention in adults aged 40 to 75 with no history of cardiovascular disease, who have 1 or more risk factors (dyslipidemia, diabetes, hypertension, or smoking), and a calculated 10-year ASCVD risk of 10% or greater.
• Osteoporosis: Screen women aged 65 or older with a dual-energy x-ray absorptiometry (DEXA) scan of the hip and lumbar spine. Screen younger postmenopausal women who are at increased risk of osteoporosis, as determined by a formal risk assessment tool (e.g., FRAX tool) showing a risk equivalent to that of a 65-year-old white woman with no additional risk factors.

CDC Adult Vaccination Schedules

Adult immunization guidelines are highly tested, especially in patients with chronic diseases or immunocompromise:

• Influenza: Administer an annual influenza vaccine to all individuals aged 6 months or older. For adults aged 65 or older, the quadrivalent high-dose inactivated influenza vaccine, recombinant influenza vaccine, or adjuvanted inactivated influenza vaccine is preferred.
• Pneumococcal Vaccination: For pneumococcal-naïve adults aged 65 or older, or those aged 19 to 64 with risk factors (e.g., chronic heart, lung, liver, or renal disease, diabetes, alcoholism, current smoking, asplenia, or immunocompromise):
  • Option 1: Administer a single dose of 20-valent pneumococcal conjugate vaccine (PCV20).
  • Option 2: Administer a single dose of 15-valent pneumococcal conjugate vaccine (PCV15) followed by a dose of 23-valent pneumococcal polysaccharide vaccine (PPSV23) at least 1 year later (can be shortened to 8 weeks in patients with immunocompromise, cerebrospinal fluid leak, or cochlear implants).
• Zoster (Shingles): Administer two doses of recombinant zoster vaccine (Shingrix) separated by 2 to 6 months in all adults aged 50 or older, regardless of prior chickenpox infection, shingles episodes, or receipt of the older live zoster vaccine (Zostavax). Shingrix is also indicated for adults aged 19 or older who are or will be immunocompromised.
• Tetanus, Diphtheria, Pertussis (Tdap/Td): Administer a single dose of Tdap to all adults who have not previously received it, followed by a Tdap or Td booster every 10 years. Pregnant patients must receive one dose of Tdap during each pregnancy, ideally between 27 and 36 weeks gestation, to provide passive immunity to the neonate.
• Hepatitis B: Screen and vaccinate all adults aged 19 to 59. For adults aged 60 or older, vaccination is recommended if they have risk factors (e.g., diabetes, healthcare exposure, sexual risk, travel) or through shared decision-making.