A 24-year-old gravida 2 para 0 presents to her physician at 15 weeks gestation to discuss the results of recent screening tests. She has no complaints and the current pregnancy has been uncomplicated. Her previous pregnancy terminated with spontaneous abortion in the first trimester. Her immunizations are up to date. Her vital signs are as follows: blood pressure 110/60 mm Hg, heart rate 78/min, respiratory rate 14/min, and temperature 36.8℃ (98.2℉). The physical examination is within normal limits. The laboratory screening tests show the following results: HBsAg negative HBcAg negative Anti-HBsAg positive HIV 1/2 AB negative VDRL positive What is the proper next step in the management of this patient?

T. pallidum hemagglutination assay

Prescription of benzylpenicillin

A 24-year-old man comes to the physician for a routine health maintenance examination. He feels well. He has type 1 diabetes mellitus. His only medication is insulin. He immigrated from Nepal 2 weeks ago . He lives in a shelter. He has smoked one pack of cigarettes daily for the past 5 years. He has not received any routine childhood vaccinations. The patient appears healthy and well nourished. He is 172 cm (5 ft 8 in) tall and weighs 68 kg (150 lb); BMI is 23 kg/m2. His temperature is 36.8°C (98.2°F), pulse is 72/min, and blood pressure is 123/82 mm Hg. Examination shows a healed scar over his right femur. The remainder of the examination shows no abnormalities. A purified protein derivative (PPD) skin test is performed. Three days later, an induration of 13 mm is noted. Which of the following is the most appropriate initial step in the management of this patient?

Administer isoniazid for 9 months

Collect sputum sample for culture

Perform interferon-γ release assay

A 27-year-old man interested in pre-exposure therapy for HIV (PrEP) is being evaluated to qualify for a PrEP study. In order to qualify, patients must be HIV- and hepatitis B- and C-negative. Any other sexually transmitted infections require treatment prior to initiation of PrEP. The medical history is positive for a prior syphilis infection and bipolar affective disorder, for which he takes lithium. On his next visit, the liver and renal enzymes are within normal ranges. HIV and hepatitis B and C tests are negative. Which of the following about the HIV test is true?

It is a qualitative test used for screening purposes.

It is a quantitative test used for screening purposes.

A secondary reagent is needed to interpret the results.

A known antigen binds directly to the patient's serum.

An unknown antigen binds to the known serum.

A 35-year-old man with no known past medical history presents to his physician because he is applying for a job as a healthcare worker, which requires screening for the hepatitis B virus (HBV). The patient states that he is in good health and denies any symptoms. His vital signs and physical exam are unremarkable. Labs are drawn, and the patient's HBV serology shows the following: HBsAg: positive anti-HBsAg antibody: negative anti-HBcAg IgM: negative anti-HBcAg IgG: positive HBeAg: negative anti-HBeAg antibody: positive Which of the following best describes this patient's results?

Chronically infected, low infectivity

Immune due to previous infection

Immune due to previous vaccination

Chronically infected, high infectivity

An endocervical swab is performed and nucleic acid amplification testing via polymerase chain reaction is conducted. It is positive for Chlamydia trachomatis and negative for Neisseria gonorrhoeae. Which of the following is the most appropriate pharmacotherapy?

Intramuscular ceftriaxone plus oral azithromycin

Intravenous cefoxitin plus oral doxycycline

A 34-year-old man comes to the physician for a routine health maintenance examination. He was diagnosed with HIV 8 years ago. He is currently receiving triple antiretroviral therapy. He is sexually active and uses condoms consistently. He is planning a trip to Thailand with his partner to celebrate his 35th birthday in 6 weeks. His last tetanus and diphtheria booster was given 4 years ago. He received three vaccinations against hepatitis B 5 years ago. He had chickenpox as a child. Other immunization records are unknown. Vital signs are within normal limits. Cardiopulmonary examination shows no abnormalities. Leukocyte count shows 8,700/mm3, and CD4+ T-lymphocyte count is 480 cells/mm3 (Normal ≥ 500); anti-HBs is 150 mIU/mL. Which of the following recommendations is most appropriate at this time?

Tetanus, diphtheria, pertussis vaccine (Tdap)

Measles, mumps, rubella vaccine

A 36-year-old man comes to the physician because of a 2-week history of productive cough, weight loss, and intermittent fever. He recently returned from a 6-month medical deployment to Indonesia. He appears tired. Physical examination shows nontender, enlarged, palpable cervical lymph nodes. An x-ray of the chest shows right-sided hilar lymphadenopathy. A sputum smear shows acid-fast bacilli. A diagnosis of pulmonary tuberculosis is made from PCR testing of the sputum. The patient requests that the physician does not inform anyone of this diagnosis because he is worried about losing his job. Which of the following is the most appropriate initial action by the physician?

Inform the local public health department of the diagnosis

Request the patient's permission to discuss the diagnosis with an infectious disease specialist

Assure the patient that his diagnosis will remain confidential

Confirm the diagnosis with a sputum culture

Notify all of the patient's household contacts of the diagnosis

A 28-year-old asymptomatic pregnant woman at 12 weeks gestation presents for prenatal care. She has no personal or family history of diabetes. Her BMI is 32 kg/m². She had a random glucose of 118 mg/dL at her first visit. She asks about gestational diabetes screening. Considering her risk factors and current pregnancy, what is the most appropriate screening approach?

Perform fasting glucose and hemoglobin A1c now to assess for preexisting diabetes

Perform 3-hour oral glucose tolerance test at 16 weeks

Diagnose gestational diabetes based on random glucose and begin treatment

Perform 1-hour glucose challenge test now

Defer screening until 24-28 weeks gestation per routine protocol

A 66-year-old man underwent screening colonoscopy which revealed a 1.2 cm tubular adenoma with low-grade dysplasia in the sigmoid colon that was completely removed. He has no family history of colorectal cancer. His colonoscopy 8 years ago was normal. He asks about surveillance recommendations. Considering current guidelines and competing risks, what is the most appropriate surveillance interval?

Repeat colonoscopy in 5-10 years

Annual fecal immunochemical testing

Infectious disease screening for USMLE Step 3: High-Yield Diagnosis Lessons

HIV Screening - Catching the Culprit

USPSTF Grade A: Screen everyone aged 15-65 years. All pregnant persons. Younger/older if at increased risk.
Approach: Routine, voluntary, "opt-out" screening is the standard of care.
High Risk: Unprotected sex, multiple partners, MSM, IV drug use, history of other STIs (TB, hepatitis).

HIV Diagnostic Testing Algorithm

⭐ 4th-generation combination assays (antigen/antibody) are preferred as they can detect the p24 antigen, shortening the diagnostic window period compared to antibody-only tests.

Hepatitis B & C - Silent Liver Stalkers

Hepatitis B (HBV) Screening:
- Universal: Screen all adults (≥18 yrs) at least once.
- High-Risk: Screen persons with a history of IV drug use, MSM, multiple sexual partners, and inmates.
- Pregnancy: Screen all pregnant women for HBsAg during each pregnancy.
- Test: HBsAg is the primary screening test.
Hepatitis C (HCV) Screening:
- Universal: Screen all adults aged 18 to 79.
- High-Risk: Anyone with IV drug use or blood transfusion before 1992.
- Test: Anti-HCV antibody, with reflex to HCV RNA PCR for confirmation.

⭐ HCV has a high rate of chronic infection (~85%), often remaining asymptomatic for decades until cirrhosis or hepatocellular carcinoma develops.

Hepatitis B Blood Test Results Interpretation

TB & Syphilis - Classic Case Files

Tuberculosis (TB):
- Presentation: Prisoner, homeless person, or immigrant with cough, night sweats, weight loss.
- Screening: TST (PPD) or IGRA. A positive screen requires a chest X-ray (CXR).
- Positive TST Cutoffs:
  - ≥5 mm: HIV+, recent TB contacts, immunosuppressed.
  - ≥10 mm: Residents of high-risk settings (prisons, hospitals), IV drug users, recent immigrants.
  - ≥15 mm: Persons with no known risk factors.
Syphilis:
- Presentation: Painless genital chancre (primary), maculopapular rash on palms/soles (secondary).
- Screening: Nontreponemal tests (VDRL, RPR).
- Confirmation: Specific treponemal tests (FTA-ABS).

⭐ High-Yield: VDRL/RPR can show biological false positives. 📌 VDRL: Viruses (e.g., mono, hepatitis), Drugs, Rheumatic fever, Lupus and Leprosy.

Chlamydia & Gonorrhea - The Youthful Plague

Screening: Annually screen all sexually active women aged <25 years.
High-Risk Factors: Screen older women with new or multiple sexual partners, or a partner with an STI.
Men: Evidence is insufficient for universal screening, but targeted screening in high-prevalence settings (e.g., MSM) is recommended.
Test of Choice: Nucleic Acid Amplification Test (NAAT) is the most sensitive test.
- Specimens: First-catch urine or swabs (endocervical, vaginal).

⭐ High-Yield Fact: Repeat testing 3 months after treatment is crucial due to high rates of reinfection, not due to treatment failure.

Vaginal Swab Self-Collection for STI Screening

High‑Yield Points - ⚡ Biggest Takeaways

HIV: Screen everyone aged 15-65 at least once, and all pregnant women.

Hepatitis C: Screen all adults aged ≥18 at least once; screen all pregnant persons during each pregnancy.

Hepatitis B: Screen all pregnant women (for HBsAg) and unvaccinated, high-risk adults.

Chlamydia & Gonorrhea: Annually screen all sexually active women aged <25 and older women at increased risk.

Syphilis: Screen all pregnant women and anyone at increased risk.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play