HomeThe 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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