5.3 Considerations for use of all screening tools

All the screening tests described above, when positive or abnormal, identify adults and adolescents living with HIV who have a higher probability of TB disease and who are then to be referred for diagnostic evaluation. TB diagnosis among people living with HIV should include use of an mWRD as a diagnostic test (12), LF-LAM where indicated (12), and other clinical, radiological or laboratory procedures as necessary.

When a screening test or algorithm is used and the results are normal or negative, if the algorithm has sufficient negative predictive value in the setting, patients should be referred for evaluation for TPT. TPT is strongly recommended for people living with HIV in whom TB disease has been ruled out (4).

As part of scale-up, tools should be first be included in the guidelines of national TB and HIV programmes and in national and local algorithms for screening and diagnostic care for people living with HIV (see 5.4 and Annex 3 for further discussion of screening algorithms for people living with HIV). Health staff will require adequate training in use of each tool, and the results of each screening test conducted should be recorded in patient clinical records.

New screening tools should not replace W4SS, which should continue to be conducted at every encounter with a health-care worker or peer supporter, regardless of the inclusion of new screening tools in the algorithm. The W4SS strengthens interpretation of the results obtained with other screening tests and is also valuable for immediate infection control measures. W4SS is also critical for indicating eligibility for an LF-LAM test if a CD4 cell count is not available (12).

Countries should include new tools for screening people living with HIV in national TB screening algorithms according to feasibility, level of health facility and available resources. Lack of access to any of the tools described in this section should not be a barrier to TB screening or ruling out TB in order to allow initiation of TPT.

Implementation considerations for CXR

Interpretation of CXR images for people living with HIV

CXR requires interpretation by a radiologist, other trained health personnel or CAD software. CXR findings may differ widely in people with HIV-associated TB, from a completely normal picture to multiple radiological abnormalities typically associated with advanced TB disease (36).

Periodicity of CXR screening

Although no data are available on the optimal periodicity of CXR screening, a pragmatic approach would be to perform CXR annually among outpatients living with HIV at the time of viral load testing or other investigations, in addition to W4SS at every encounter with a health worker between annual screens. The frequency might be determined according to the regularity of ART, use of TPT and TB transmission setting. A baseline CXR and access to films taken previously are useful for comparing subsequent radiological changes. (See 3.1.2 for further considerations for screening with CXR).

Service delivery

HIV services should be integrated with TB and radiography services to maintain a “one-stop shop”. It is essential to engage with local civil society organizations, given that this screening approach is most relevant for people living with HIV who are stable, in care, immunocompetent and likely to be supported in the community. The risks of exposure to ionizing radiation, especially from non-compliant equipment, might be a greater concern for this group, who undergo CXR regularly and may also receive radiography to evaluate health problems between screenings.

Implementation considerations for CRP

Choice of cut-off value

CRP at cut-off values of either > 5 mg/L or > 10 mg/L is similarly or more accurate than W4SS. The cut-off of > 5 mg/L is recommended because it is the lowest threshold that indicates abnormality in many clinical settings and is more sensitive. The choice of cut-off value will, however, depend on the availability of CRP technology, the prevalence of other conditions that may increase CRP values and a preference for increased sensitivity or increased specificity.

Requirements and service delivery

Currently, many analysers are available for measuring CRP at points of care, with different levels of detection, although all can be used for TB screening with a CRP cut-off between 5 and 10 mg/L. The results obtained with most quantitative point-of-care analysers are strongly correlated with those of laboratory analysers.

Like finger-stick measurement of glucose with a glucometer, point-of-care CRP tests provide rapid (≤ 5 min) quantitative results from capillary blood (obviating the need for phlebotomy) and are simple enough to be performed by front-line health-care workers after minimal training. Containers for safe disposal of needles and other sharp tools for pricking the finger must be available, and other infection control measures in the collection of blood must be followed.

The overall laboratory requirements are minimal; however, most analysers require a continuous electricity source, and most CRP assays require cold storage and refrigeration (+2 to +8 °C). Some semi-quantitative test strips are available with operational characteristics ideal for use in remote settings (inexpensive, no analyser required); however, the agreement of results with those of laboratory analysers is moderate and may decrease further if time-to-test strip interpretation exceeds 5 min.

If point-of-care testing for CRP is not available, blood samples will have to be sent to the nearest laboratory, which will significantly undermine the utility of the test for on-the-spot decision-making and render it less useful for screening in outpatient settings.

Implementation considerations for mWRD

Resource requirements

Use of mWRDs for screening in addition to diagnostic testing represents a significant shift and requires significant resources. (See Annex 3 on modelled algorithms.) Providers and health staff require training in the proper use and interpretation of mWRDs when used for screening.

Service delivery

Depending on feasibility and available resources, countries may choose to prioritize TB screening with mWRDs in certain subpopulations other than those for whom it is generally recommended, such as medical inpatients in settings where the TB prevalence is < 10% or pregnant women living with HIV.

Use of mWRDs for screening among outpatients with HIV in regular ART care should be aligned with regular HIV services (e.g. viral load monitoring). Similarly, for pregnant women with HIV, it should be aligned with antenatal services.

To use of mWRDs to screen medical inpatients with HIV, the TB prevalence in medical wards may be calculated as the percentage of admissions that are diagnosed with TB during a recent 6–12- month period. Prevalence is calculated for all inpatients, not just those with HIV, to reflect the risk of transmission and the burden of disease in the community.

See 3.1.4 for further considerations on screening with mWRDs.

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