Clinical utility of a commercial LAM-ELISA assay for TB diagnosis in HIV-infected patients using urine and sputum samples.
BACKGROUND
The accurate diagnosis of TB in HIV-infected patients, particularly with advanced immunosuppression, is difficult. Recent studies indicate that a lipoarabinomannan (LAM) assay (Clearview-TB(R)-ELISA) may have some utility for the diagnosis of TB in HIV-infected patients; however, the precise subgroup that may benefit from this technology requires clarification. The utility of LAM in sputum samples has, hitherto, not been evaluated.


METHODS
LAM was measured in sputum and urine samples obtained from 500 consecutively recruited ambulant patients, with suspected TB, from 2 primary care clinics in South Africa. Culture positivity for M. tuberculosis was used as the reference standard for TB diagnosis.


RESULTS
Of 440 evaluable patients 120/387 (31%) were HIV-infected. Urine-LAM positivity was associated with HIV positivity (p = 0.007) and test sensitivity, although low, was significantly higher in HIV-infected compared to uninfected patients (21% versus 6%; p<0.001), and also in HIV-infected participants with a CD4 <200 versus >200 cells/mm(3) (37% versus 0%; p = 0.003). Urine-LAM remained highly specific in all 3 subgroups (95%-100%). 25% of smear-negative but culture-positive HIV-infected patients with a CD4 <200 cells/mm(3) were positive for urine-LAM. Sputum-LAM had good sensitivity (86%) but poor specificity (15%) likely due to test cross-reactivity with several mouth-residing organisms including actinomycetes and nocardia species.


CONCLUSIONS
These preliminary data indicate that in a high burden primary care setting the diagnostic usefulness of urine-LAM is limited, as a rule-in test, to a specific patient subgroup i.e. smear-negative HIV-infected TB patients with a CD4 count <200 cells/mm(3), who would otherwise have required further investigation. However, even in this group sensitivity was modest. Future and adequately powered studies in a primary care setting should now specifically target patients with suspected TB who have advanced HIV infection.
Dheda
Keertan
K
Lung Infection and Immunity Unit, Department of Medicine, Division of Pulmonology and Clinical Immunology, UCT Lung Institute, University of Cape Town, Cape Town, South Africa. keertan.dheda@uct.ac.za
Davids
Virginia
V
Lenders
Laura
L
Roberts
Teri
T
Meldau
Richard
R
Ling
Daphne
D
Brunet
Laurence
L
van Zyl Smit
Richard
R
Peter
Jonathan
J
Green
Clare
C
Badri
Motasim
M
Sechi
Leonardo
L
Sharma
Surendra
S
Hoelscher
Michael
M
Dawson
Rodney
R
Whitelaw
Andrew
A
Blackburn
Jonathan
J
Pai
Madhukar
M
Zumla
Alimuddin
A
D000328:Adult; D000465:Algorithms; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D015658:HIV Infections / Q000150:complications* / Q000378:metabolism / Q000652:urine / Q000821:virology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000378:metabolism; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013183:Sputum / Q000378:metabolism; D016896:Treatment Outcome; D014376:Tuberculosis / Q000150:complications* / Q000175:diagnosis* / Q000276:immunology* / Q000378:metabolism / Q000652:urine; D016482:Urinalysis