Investigations
1st investigations to order
FBC with differential
Test
To screen for aneamia or lymphocytopenia. Common finding in disseminated Mycobacterium avium complex.[18]
Result
low Hb; reduced CD4+ count
LFT
Test
To screen for elevated liver enzymes. Common finding in disseminated Mycobacterium avium complex.[18]
Result
elevated alkaline phosphatase
chest x-ray
Test
Should be compared with baseline x-rays (if available) to document progression.
Result
thin-walled cavitary lesions primarily in the upper lobes; or nodules and bronchiectasis in the middle or lower lobes
sputum culture
Test
Positive sputum cultures do not necessarily indicate Mycobacterium avium complex (MAC) pulmonary disease. Are confirmatory following clinical assessment and radiographs.
Could reflect colonisation only.
Result
positive for growth of MAC
blood culture
Test
In HIV-related disseminated Mycobacterium avium complex (MAC), blood cultures are very helpful in establishing the diagnosis. The sensitivity of a single blood culture to yield the diagnosis is 90% to 95%; two blood cultures have a sensitivity of 99%.[38]
Result
positive for growth of MAC
Investigations to consider
high-resolution CT (HRCT) scanning
Test
Abnormal chest x-ray but without cavitations should prompt HRCT.
Result
thin-walled upper lobe cavities; multiple, peripheral nodules centred on the bronchovascular tree ('tree-in-bud'); cylindrical bronchiectasis
bone marrow aspirate for culture
Test
May be required in cases of suspected disseminated Mycobacterium avium complex (MAC) if blood cultures are non-diagnostic.
Result
positive for growth of MAC
bronchoscopy/bronchial lavage
Test
May be required in patients with radiographical changes if sputum cultures are non-diagnostic.
Result
positive for growth of Mycobacterium avium complex
lung biopsy
Test
May be required in patients with radiographical changes if sputum cultures are non-diagnostic.
Result
granulomas; centrilobular and bronchiolocentric distribution in cases of hypersensitivity pneumonitis; culture positive for growth of Mycobacterium avium complex
lymph node biopsy
Test
May be required in children presenting with cervical lymphadenopathy.
Result
granulomas; culture positive for growth of Mycobacterium avium complex
Emerging tests
polymerase chain reaction
Test
A promising test to detect Mycobacterium avium complex (MAC) directly in the blood in cases of disseminated MAC.
Result
detection of DNA
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