TB or Not TB Test Only PDF

TB or Not TB At risk populations: • Children under 4 exposed to high-risk adults • Clinical /medical conditions that lower the immune system TB Skin Testing (Mantoux TB skin test) • Looks for delayed hypersensitivity (type IV) • Read at 48-72 hrs post inoculation • Induration measured in mm (diamete...

TB or Not TB At risk populations: • Children under 4 exposed to high-risk adults • Clinical /medical conditions that lower the immune system TB Skin Testing (Mantoux TB skin test) • Looks for delayed hypersensitivity (type IV) • Read at 48-72 hrs post inoculation • Induration measured in mm (diameter) Threshold for Positive Tests • Diameter (mm) based on what category of risk pt falls into o Low Risk § ≥ 15 mm § No risk factors o Moderate Risk § ≥10 mm § Pts with diabetes, renal failure, cancers (H/N, lung, lymphoma, leukemia, etc) o High risk § ≥ 5 mm § HIV infection § Fibrosis on chest x-ray § Recent contact w a person who has active TB § Immunosuppression (drugs and system) Potential Causes of False Negative TB tests • Technical (correctable): Administrator’s fault • Biologic (not correctable): Infections, Recent LIVE virus vaccines (measles, mumps, polio) Chest X-Ray Results: TB positive will have calcified granulomas Clinical Manifestations • Sometimes no symptoms • Symptoms when present: o Weight loss o Night sweats o Cough o Low grade fever o Fatigue o Chest pain o Hemoptysis Interferon Gamma Release Assays (IGRA) • T-Spot, QuantiFERON Gold o Blood test: no 2-3 day return for PPD reading o Does not distinguish btwn latent/active o T-Spot: Sensitivity higher in HIV pt o QuantiFERON TB gold: § For individuals who previously had TB positive skin test and received BCG vaccination § QuantiFERON TB gold does not cross react w BCG § Not affected by BCG or non-TB mycoplasma (no false neg present) Other Methods for ID • Sputum Smear: acid fast bacteria (ABF stain) • Cultures: Sputum Nucleic Acid Amplification (NAA) • Test for rapid diagnosis of M. tuberculosis • Finds TB in 50-80% of AFB neg smears • Can distinguish between TB and non-TB • Culture still REQUIRED for susceptibility • Recommended first line (WHO) Primary Infection • Infection of an individual lacking previous contact or immune response to tubercle bacilli • Occurs after initial infection/exposure of Mycobacterium tuberculosis/Mycobacterium bovis • Primary Sites: o Lungs (primary TB, mycobacterium tuberculosis) o Tonsils o Intestine o Skin Pathophysiology of Primary infection TB causes lymphangitis in which lymph nodes? • Inhalation of droplet nuclei (no more than 3 bacilli) • macrophages burst (bacteria comes out of macrophage) • Spread to regional lymph nodes • Enlargement of hilar lymph node à Lymphangitis • If it spreads, it gives rise to miliary TB (gets out of lungs & spread to other organs) • If it stay in place it forms Primary Ghon’s Complex (healed calcification) o Seen in untreated primary pulmonary TB with Ghon’s fibrosis (calcified granuloma) • Summary o Ghon’s focus on lungs (gradually fills, calcifies into Ghon’s Body) o Lymphangitis o Enlargement of hilar lymph nodes (Hilar lymph-adenitis) o Manifests 3wks after primary TB infection, granulomas forms o Can spread to bloodstream (miliary TB) Secondary Infection (Re-Infection) • Lymphokine activates macrophages • Macrophage secrete cytokines • Anoxia and necrosis occurs • Vigorous pus forms • Macrophages transform to epithelioid cells • Aggregation of epithelial cells with giant cell (Langhan’s type) and fibrosis seen • Formation of tubercle and manifestation of clinical signs: o Chronic cough for 3+ wks o Fiber fever o Chest pain o Shortness of breath o Loss of weight • Summary o Lesion on apex of lung(s) o Begins as small focus of consolidation (<3cm) o Shows granulomas of epithelioid cells with Langhan’s giant cells Extra Pulmonary Sites of TB • Pleural • Miliary (spreads to other organs) • Lymphatic • Meninges Diagnosis and Tx drugs: • Chest x-ray • First line drugs (4): o Rifampin o Isoniazid o Pyrazinamide o Ethambutol Traits Age Incidence Site of Parenchymal Lesion Characteristic Lesion Fate Primary Pulmonary TB • Children • Subpleural lesion • Ghon’s focus • Ghon’s Complex • Heal by calcified scar Primary Infection makes Ghon’s Complexes Secondary Infection is the transformation of Ghon’s to the manifestation of symptoms Secondary Pulmonary TB • Adult • Apex has Subapical lesion • R lung • Tubercle formation • No regional lymph node involvement • Fibrocalcific scar if healed, or Progressive pulmonary TB