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
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
Samples
Type of sample
– Sputum (resp. sample), CSF (spinal/paraspinal/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!