What laboratory tests should be included for screening for communicable diseases?

Laboratory Screening for Communicable Diseases

The core screening panel for communicable diseases should include HIV antibody/antigen testing, hepatitis B surface antigen (HBsAg), hepatitis C antibody, syphilis serology (RPR or treponemal-specific test), and for sexually active individuals, testing for gonorrhea and chlamydia. 1

Essential Screening Tests for All Populations

Blood-Borne Pathogens

• HIV Testing: Use enzyme-linked immunoassay (EIA) for both HIV-1/2 antibodies and antigen as the preferred initial test, with repeatedly reactive results confirmed by Western immunoblot 1
• Hepatitis B: Screen with HBsAg, and consider adding hepatitis B core antibody (HBcAb) and hepatitis B surface antibody (anti-HBs) for complete immunity assessment 1
• Hepatitis C: Screen with hepatitis C antibody testing 1
• Syphilis: Most laboratories now use reverse screening algorithms with treponemal-specific tests first (EIA/chemiluminescence immunoassay) followed by nontreponemal testing (RPR) to confirm 1

Sexually Transmitted Infections

• Gonorrhea and Chlamydia: Test all sexually active individuals, with mandatory screening for women under 25 years and consideration for all men and women aged ≥25 years based on risk factors 1
• Trichomonas: Screen all women 1
• High-risk populations (MSM): Include extragenital site testing (rectal, oropharyngeal) for gonorrhea and chlamydia 1

Additional Screening Based on Risk Factors

For HIV-Positive or Immunocompromised Patients

• Toxoplasma gondii serology: Essential for risk stratification 1
• CMV IgG antibody: Particularly for patients at low baseline risk 1
• Tuberculosis screening: Tuberculin skin test or interferon-gamma release assay 1
• Hepatitis A total antibody: To determine need for vaccination 1

For Pregnant Women

• First trimester or initial prenatal visit: HIV, syphilis serology, HBsAg, gonorrhea, and chlamydia (if under 25 or high-risk) 1
• Third trimester repeat: HIV testing (even if previously tested), syphilis in high-risk populations, and chlamydia for at-risk women 1
• 35-37 weeks gestation: Group B streptococcus screening using both vaginal and rectal swabs 1

Critical caveat: No infant should leave the hospital without maternal syphilis status determined at least once during pregnancy and preferably again at delivery 1

Screening Frequency Considerations

High-Risk Populations Requiring More Frequent Testing

• Sexually active HIV-infected persons: Annual syphilis screening at minimum, with testing every 3-6 months for those with multiple partners, unprotected intercourse, methamphetamine use, or partners engaging in such activities 1
• MSM: More frequent STI screening (every 3-6 months) given higher transmission rates 1
• Individuals with new STD diagnoses: Rescreen for other STIs as co-infection is common 1

Special Testing Scenarios

Transplant Donor/Recipient Screening

Both donors and recipients require comprehensive screening including 1:

• HIV 1/2 antibody (with nucleic acid testing for high-risk donors)
• HBsAg, HBcAb, and anti-HBs
• HCV antibody
• CMV IgG and EBV IgG antibodies
• Toxoplasma IgG (especially for heart transplant)
• Syphilis serology (RPR or equivalent)
• Tuberculin skin testing (recipients)
• Blood cultures (donors)

Genital Lesion Evaluation

When genital lesions are present 1:

• Syphilis serology (mandatory)
• HSV testing via NAAT (preferred over culture for highest sensitivity and HSV typing)
• HIV screening (inflammatory epithelium enhances HIV transmission risk)
• Consider Haemophilus ducreyi testing where chancroid is prevalent

Important pitfall: Viral culture for HSV is less sensitive than NAAT, particularly for ulcerative (versus vesicular) lesions, recurrent lesions, and in immunocompetent patients 1, 2

Laboratory Test Interpretation Nuances

• Syphilis: Biologic false-positive RPR/VDRL results are typically low titer (<1:8) and may be associated with injection drug use history 1
• HIV window period: Transient increases in HIV viral load can occur with vaccinations and intercurrent illnesses 1
• HSV serology limitations: Point-of-care antibody tests should not be used in low-risk populations due to high false-positive rates; type-specific glycoprotein G-based assays are required to distinguish HSV-1 from HSV-2 1, 2

Partner Management

Whenever a communicable disease diagnosis is made, sexual contacts must be evaluated and given presumptive treatment to prevent reinfection, as most treatment "failures" represent reinfection from untreated partners 1