Synopsis
Detect active and latent infections before immune control is weakened, interpret imperfect tests in context, complete prevention safely and avoid delaying urgent treatment without an agreed containment plan.
- Screen before the first immunosuppressive dose whenever possible, because corticosteroids and targeted agents reduce test sensitivity, accelerate reactivation and narrow vaccination options.
- Begin with birthplace, residence and travel, TB contact and treatment, blood and sexual exposure, previous hepatitis, recurrent infection, VZV history, vaccines, prior biologics and planned drug mechanism.
- TB assessment combines symptom review, examination, chest radiography and IGRA, with TST added when appropriate; no single test is a gold standard for latent infection.
- A positive IGRA or TST indicates immune sensitisation, not proof of latency: exclude active tuberculosis clinically, radiologically and microbiologically before preventive treatment.
- Hepatitis B screening requires HBsAg, total anti-HBc and anti-HBs; if HBsAg or anti-HBc is positive, obtain HBV DNA and specialist risk stratification.
- Check hepatitis C antibody with confirmatory RNA after a reactive result and offer HIV antigen-antibody testing according to the treatment pathway and current national practice.
- Use exposure-driven Strongyloides assessment before corticosteroids or major immunosuppression and establish VZV immunity and vaccination needs before live vaccines become unsafe.
- A screen is not a one-off guarantee: new exposure, travel, symptoms or a changed immune regimen requires renewed risk assessment even when baseline tests were negative.
Key red flags
Cough, fever, weight loss, night sweats, haemoptysis, lymphadenopathy or abnormal chest imaging requires active-tuberculosis investigation and appropriate respiratory isolation before latent treatment.
Jaundice, coagulopathy, encephalopathy or major aminotransferase elevation with positive hepatitis markers needs urgent hepatology assessment rather than routine pre-treatment clearance.
Abdominal or respiratory deterioration, Gram-negative bacteraemia, meningitis or serpiginous rash after corticosteroids in an exposed person suggests Strongyloides hyperinfection.
A widespread vesicular rash, ocular symptoms, meningism or neurological change indicates active VZV or HSV disease, not merely absent immunity.
A negative IGRA, absent eosinophilia or negative antibody result during existing immunosuppression can be falsely reassuring and must not override a high-risk history or syndrome.
Rituximab, stem-cell transplantation, intensive chemotherapy and high-dose corticosteroids can create reactivation risk that requires specialist prophylaxis before every pending result is available.
Constitutional, respiratory, nodal, spinal, abdominal or neurological symptoms and abnormal imaging require site-specific microbiology before the result is classified as latent infection.
Investigation priorities
Set pre-test probability, identify active symptoms and determine which latent or vaccine-preventable infections matter for the planned mechanism.
Identify immune sensitisation and radiographic evidence of previous or current tuberculosis before biologic or substantial immunosuppressive treatment.
Management branches
A biologic, targeted drug, conventional immunosuppressant, prolonged corticosteroid course, chemotherapy or transplantation is being planned.
- Define the treatment mechanism, expected intensity and start date, then take a structured infection, travel, vaccination and previous-treatment history.
- Check FBC, renal and liver profiles and complete core infection testing early enough to act on results without unnecessary therapeutic delay.
- Add exposure- and protocol-specific tests such as Strongyloides, VZV, CMV, EBV or toxoplasma rather than ordering an undirected universal panel.
- Assign each positive, indeterminate or pending result to a named TB, hepatology, infection, sexual-health, virology or tropical-medicine pathway.