The following are suggested for each laboratory reporting system:
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Established turnaround times and reporting parameters for each testing methodology (Table 2) should be readily available in the laboratory standard operating procedures.
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Reports should be dated and indicate the laboratory microbiologist overseeing the analyses.
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Reported information should be disseminated by a digital laboratory information system that is accessible to the submitting clinician, via secure telephone, facsimile or e-mail, within 24 hours of test completion.
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Preliminary results (e.g., new AFB positive) and critical changes (eg, NTM reclassified as M. tuberculosis) should be communicated immediately to the submitting physician, ideally by phone.
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The submitting physician and public health should be notified as soon as suspected or confirmed resistant TB are detected.
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Reports on non-standardized testing (such as antimicrobials not recommended by the CLSI for susceptibility testing) should indicate these limitations.
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Turnaround times for microscopy and NAATs should be monitored periodically (monthly) to check compliance and evaluated annually.
Table 1. Number of bacteria seen on microscopy and laboratory interpretation.a
Number of AFB seen by staining methods | ||
---|---|---|
Fuchsin stain (Kinyoun) (1000x magnification)b | Fluorochrome (Auramine) (250x magnification) | Semi-quantitative grading system: Report |
0 in 300 fields | 0 in 30 fields | Negative |
1-2 per 300 fields | 1-2 per 30 fields | Inconclusive, repeat |
1-9 per 100 fields | 1-9 per 10 fields | 1+ (rare) |
1-9 per 10 fields | 1-9 per field | 2+ (few) |
1-9 per field | 10-90 per field | 3+ (moderate) |
>9 per field | >90 per field | 4+ (numerous) |
Abbreviation: AFB, acid-fast bacilli.
a From Canadian Tuberculosis Standards, 7th Edition. Public Health Agency of Canada.
b All reports should state staining method used and actual number of organisms observed.
Table 2. Summary of suggested turnaround times (refer to individual section for more information). 28
Procedure | Turnaround time to completion/report |
---|---|
Specimen collection and arrival at the first laboratory | 24 hours |
AFB smear microscopy | 24 hours from specimen receipt, where available |
Nucleic acid amplification testing (NAAT) for M. tuberculosis detection | <7 days from smear result or 24 hours from receipt of specimen if AFB smear is not locally available |
Identification of mycobacterial isolate as M. tuberculosis complex (or non-tuberculous mycobacteria) | 2 days from positive culture |
Primary phenotypic susceptibility testing | 3 weeks from a positive culture received in reference laboratories, depending on antibiotic |
Reporting of all test results | 24 hours from test completion |
Abbreviation: AFB, acid-fast bacilli.
Table 3. QuantiFERON®-TB Gold Plus interpretive criteria (manufacturer’s recommendations).
Nil (IU/mL) | TB1 and/or TB2 antigen minus nil (IU/mL) | Mitogen minus nil (IU/mL) | QuantiFERON®-TB (IU/mL) | Report/Interpretation |
---|---|---|---|---|
≤ 8.0 | <0.35 | ≥ 0.5 | Negative | M. tuberculosis infection not likely |
≥ 0.35 and < 25% of Nil value | ≥ 0.5 | |||
≥ 0.35 and ≥ 25% of Nil value | Any | Positive | M. tuberculosis infection likely | |
<0.35 | <0.5 | Indeterminate | Results are indeterminate for TB-Antigen responsiveness. Please repeat if clinically indicated. |
|
≥ 0.35 and < 25% of Nil value | <0.5 | |||
> 8.0 | Any | Any |
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