3.10 Biopsies, laboratory tests on body fluids and other biological tests
3.10.1 Biopsies and fine needle aspirate cytology (FNAC)
Biopsies of lymph nodes, bone and pleural lining are often not feasible in resourceconstrained settings given the technical skill and laboratory resources required. The cytology of the lymph nodes from FNAC is easier to perform. Specific granulomatous tissue, the presence of giant Langhans' cells, and/or caseous necrosis strongly correlate with TB. AFBs are not always present. For the procedure for FNAC, see Appendix 4.
Note: molecular tests can be used on the specimens obtained from FNAC of lymph nodes.
3.10.2 Laboratory tests on body fluids
The diagnosis of some EPTB localisations can be supported or confirmed by a combination of tests performed in respective body fluids.
Table 3.2 - Summary of findings suggestive of TB in body fluids
Fluids | Tests |
Ascitic fluid |
|
Pleural fluid |
|
Cerebrospinal fluid |
|
Urine |
|
3.10.3 Other biological examinations
New TB diagnostic tests are in development for point-of-care use. These antigen-detection assays are based on detecting liporabinomannan (LAM): a carbohydrate cell wall antigen that is excreted in the urine of TB patients. The performances of the LAM urine assay for most populations are poor. An exception is the sensitivity of the LAM assay in patients with CD4 counts < 20033,34,35. The test may have some utility where advanced HIV-associated immunodeficiency is common.
Sedimentation rate is almost always higher but this examination is very non-specific. A normal sedimentation rate makes TB less likely but still possible.
C-reactive protein is also generally increased but this test also is very non-specific.
There exist commercial rapid blood tests for “serological diagnosis of TB”, but they are so far not very reliable in diagnosing active TB and should not be used.