Standards for Laboratory Diagnosis of Tuberculosis

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Standards for Laboratory Diagnosis of Tuberculosis

• Professor Brian I. Duerden
• Inspector of Microbiology and Infection Control,
• Department of Health

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TB diagnosis and management depend upon a
reliable and prompt laboratory service
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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

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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

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Standards to cover

• 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

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Samples

• Type of sample
• Sputum (resp. sample), CSF (spinal/para-spinal/int
  ra-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

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Transfer to laboratory

• Within 24h (or 1 working day, max 48h)
• Minimise overgrowth
• Maintain AFB character
• Potentially infected clinical sample
• Routine procedure

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Immunodiagnostic tests

• Interferon ? (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?

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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

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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

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Standards for Quality

• Only do what you can do properly!