How do I order a varicella titer?

How to Order a Varicella Titer

To order a varicella titer, request a "Varicella-Zoster Virus (VZV) IgG Antibody Test" through your laboratory system, specifying that you need quantitative results rather than just positive/negative status. This test is essential for determining immunity to varicella, especially in healthcare settings where evidence of immunity is required.

Test Selection and Interpretation

• Test name: Varicella-Zoster Virus (VZV) IgG Antibody Test
• Specimen type: Serum sample (typically 3-5 mL of blood in a red-top or tiger-top tube)
• Purpose: To determine immunity to varicella (chickenpox)

Important Considerations:

• Commercial enzyme immunoassay (EIA) and latex agglutination tests are commonly available but have limitations 1:
  • These tests are less sensitive for detecting vaccine-induced immunity compared to natural infection
  • Latex agglutination tests may yield false-positive results
  • More sensitive tests like gpELISA and FAMA exist but are not commercially available

When to Order Varicella Titers

Varicella titers should be ordered for:

1. Healthcare personnel without documented evidence of immunity 1

   • Birth before 1980 is NOT considered evidence of immunity for healthcare workers
   • Serologic screening before vaccination is cost-effective for those with negative/uncertain history

2. Adults with uncertain immunity status who need verification 1

   • Particularly important before starting immunosuppressive therapy
   • For those with negative or uncertain history of varicella

3. Pregnant women with uncertain immunity status

   • To determine need for post-exposure prophylaxis if exposed

Interpreting Results

• Positive titer: Indicates immunity to varicella (either from natural infection or vaccination)
• Negative titer: Indicates susceptibility to varicella

Pitfalls in Interpretation:

• A positive history of varicella has high positive predictive value (reliable indicator of immunity) 2
• A negative history has low predictive value (many with negative histories are actually immune) 2
• Standard commercial assays may miss low-level antibodies present after vaccination 3
  • In one study, 10% of previously vaccinated healthcare workers had nonprotective titers 4

Follow-up Actions Based on Results

• Negative titer:

  • For healthy adults: Recommend 2-dose varicella vaccination series 4-8 weeks apart 1
  • For immunocompromised patients: Consider VZIG for post-exposure prophylaxis if exposed 1

• Positive titer:

  • Document immunity in medical record
  • No further action needed

Special Considerations for Healthcare Settings

• Healthcare institutions should establish protocols for screening and managing personnel 1
• For healthcare workers with negative titers despite vaccination, consider more sensitive testing methods before additional vaccine doses 3
• In cases of persistent serologic non-response despite vaccination, lymphocyte proliferation assays may be considered to assess cell-mediated immunity 3

Remember that commercially available tests were designed to detect higher antibody levels associated with natural infection rather than the lower levels induced by vaccination, which may lead to false-negative results in vaccinated individuals 3.