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Standards for Laboratory Diagnosis of Tuberculosis. Professor Brian I. Duerden Inspector of Microbiology and Infection Control, Department of Health. TB diagnosis and management depend upon a reliable and prompt laboratory service. Guidance and Standards. National SOP How to do the tests
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Standards for Laboratory Diagnosis of Tuberculosis Professor Brian I. Duerden Inspector of Microbiology and Infection Control, Department of Health
TB diagnosis and management depend upon a reliable and prompt laboratory service
Guidance and Standards • National SOP • How to do the tests • NICE guidance • How to manage the patient • DH programme • What service should be delivered • 3 working groups
TB monitoring and laboratory services working group • Surveillance standards • Standards for laboratory diagnosis • Current best practice • Simple and straightforward • Not replicate or replace the National SOP
Samples Transfer to laboratory Immediate tests Microscopy Culture, isolation and identification Laboratory facilities and expertise Transport Susceptibility testing Molecular fingerprinting/typing Notification PCR detection of Mtb Immunodiagnostic tests Histopathology Standards to cover
Samples • Type of sample • Sputum (resp. sample), CSF (spinal/para-spinal/intra-cerebral), gastric washings, lymph nodes (tissues), urine, faeces • Number of samples • 2 or 3 for sputum? Consecutive days. • Early morning or any time? • True LRT specimen • Documentation
Transfer to laboratory • Within 24h (or 1 working day, max 48h) • Minimise overgrowth • Maintain AFB character • Potentially infected clinical sample • Routine procedure
Immediate tests • Microscopy • Auramine fluorescent staining • 6-day service (not on call) • Perform microscopy and issue result within 24h (1 working day) of receipt • Telephone positive result to senior member of clinical team • Notify lead TB nurse, lead clinician, CCDC • Accreditation; IQC programme; satisfactory EQA performance; staff CPD/peer review
Culture, isolation and identification • Automated liquid culture on all samples • Set up within 24h of receipt (6 day service) • Plus conventional solid culture • Send all isolates to RCM on day found to be positive • Reach RCM within 24h • Complete identification of most mycobacterial isolates within 21 days
Identification and reporting • NAAT (PCR, LCR) or hybridisation gene probe for Mtb complex • On the day culture shows positive OR • Within 24h of receipt at RCM • Other probes and/or phenotypic tests • Report on day of test to • Senior member of clinical team • Lead TB nurse, lead TB clinician, CCDC
Laboratory facilities and expertise • Safety – Category 3 for culture • HSE approved • Contingency plan for accidental dispersal • Continuity plan for closure • Accredited • IQC programme, satisfactory EQA • Sufficient number – daily service, competence • Named Consultant and BMS for advice
Transport • Samples • Potentially infected samples (routine) • Positive cultures • Category A but exemption to treat as B for clinical and diagnostic purposes • UN 3373 – marked Diagnostic or Clinical • P650 packaging • Do not send by Royal Mail
Susceptibility testing • Complete within 30 days of initial receipt of clinical sample for primary agents • Isoniazid, rifampicin, pyrazinamide, ethambutol • Takes 10-20 days by liquid proportion (automated) or resistance ratio • Molecular detection • Rifampicin within 24h if MDRTB suspected • Isoniazid under development • Done at RCM with accreditation, IQC, EQA
Molecular fingerprinting/typing • ALL ISOLATES • 15-loci MIRU-VNTR • Mycobacterial Interspersed Repetitive Units – Variable Number Tandem Repeats • Results to national database • Other techniques as appropriate • Done at RCM
Laboratory notification • HPA • Via CoSurv from laboratory that identifies a positive culture • Confirmation of positive from RCM within 24h (1 working day) of receipt • RCM reports culture and susceptibility results to MycobNET within 24h of report to clinician
PCR detection of Mtb • Not routine • Available from RCM for particular samples • High suspicion • Definitive diagnosis deemed to be urgent • Liaise in advance – Consultany Microbiologist to RCM
Immunodiagnostic tests • Interferon γ (QuantiFERON-TB Gold) • Activated specific T-cells (T-SPOT.TB) • Standard under development • Which patients? • How long should it take? • Who provides it? • What do the results mean and who interprets them?
Histopathology • Report within 3 days of receipt • Inform the Microbiology service • Ensure same reporting as for positive microscopy and culture results • Send autopsy samples to Microbiology without formalin!! • [Role of PCR to be determined]
Implementation of standards • Local responsibility • What is done where? • Microscopy; culture; identification • What throughput is needed? • Equipment – cost-effectiveness • Personnel • Maintain skills; CPD; peer review • Named individuals for advice • Back-up and cover • IQC, EQA
Standards for Quality Only do what you can do properly!