Diagnostic accuracy of a point-of-care urine test for tuberculosis screening among newly-diagnosed hiv-infected adults: a prospective, clinic-based study
BMC Infectious Diseases
Diagnostic accuracy of a point-of-care urine test for tuberculosis screening among newly-diagnosed hiv-infected adults: a prospective, clinic-based study
Paul K Drain 0 1 4 5
Elena Losina 0 1 2 4
Sharon M Coleman 2
Janet Giddy 7
Douglas Ross 6
Jeffrey N Katz 0 4
Rochelle P Walensky 0 1 4
Kenneth A Freedberg 0 1 4
Ingrid V Bassett 1
0 Brigham and Women's Hospital , Boston , USA
1 Division of Infectious Diseases and Medical Practice Evaluation Center, Massachusetts General Hospital , Boston , USA
2 Boston University School of Public Health , Boston , USA
3 943 , Boston, MA 02114 , USA
4 Brigham and Women's Hospital , Boston , USA
5 Medical Practice Evaluation Center, Department of Medicine, Massachusetts General Hospital , 50 Staniford St
6 St. Mary's Hospital , Durban , South Africa
7 McCord Hospital , Durban , South Africa
Background: A rapid diagnostic test for active tuberculosis (TB) at the clinical point-of-care could expedite case detection and accelerate TB treatment initiation. We assessed the diagnostic accuracy of a rapid urine lipoarabinomannan (LAM) test for TB screening among HIV-infected adults in a TB-endemic setting. Methods: We prospectively enrolled newly-diagnosed HIV-infected adults (18 years) at 4 outpatient clinics in Durban from Oct 2011-May 2012, excluding those on TB therapy. A physician evaluated all participants and offered CD4 cell count testing. Trained study nurses collected a sputum sample for acid-fast bacilli smear microscopy (AFB) and mycobacterial culture, and performed urine LAM testing using Determine TB LAM in the clinic. The presence of a band regardless of intensity on the urine LAM test was considered positive. We defined as the gold standard for active pulmonary TB a positive sputum culture for Mycobacterium tuberculosis. Diagnostic accuracy of urine LAM was assessed, alone and in combination with smear microscopy, and stratified by CD4 cell count. Results: Among 342 newly-diagnosed HIV-infected participants, 190 (56%) were male, mean age was 35.6 years, and median CD4 was 182/mm3. Sixty participants had culture-positive pulmonary TB, resulting in an estimated prevalence of 17.5% (95% CI 13.7-22.0%). Forty-five (13.2%) participants were urine LAM positive. Mean time from urine specimen collection to LAM test result was 40 minutes (95% CI 34-46 minutes). Urine LAM test sensitivity was 28.3% (95% CI 17.5-41.4) overall, and 37.5% (95% CI 21.1-56.3) for those with CD4 count <100/mm3, while specificity was 90.1% (95% CI 86.0-93.3) overall, and 86.9% (95% CI 75.8-94.2) for those with CD4 < 100/mm3. When combined with sputum AFB (either test positive), sensitivity increased to 38.3% (95% CI 26.0-51.8), but specificity decreased to 85.8% (95% CI 81.1-89.7). Conclusions: In this prospective, clinic-based study with trained nurses, a rapid urine LAM test had low sensitivity for TB screening among newly-diagnosed HIV-infected adults, but improved sensitivity when combined with sputum smear microscopy.
Tuberculosis; HIV/AIDS; Lipoarabinomannan (LAM); Urine; Diagnostic testing; Screening; South Africa
Mycobacterium tuberculosis accounts for 25% of the 2
million AIDS-related deaths annually, and global health
leaders have set a target of detecting the vast majority of
infectious tuberculosis cases by 2015 [1,2]. However, given
the existing diagnostic tests, implementing a sensitive,
costeffective screening strategy among HIV-infected adults will
be challenging . Sputum smear microscopy has poor
diagnostic sensitivity among HIV-infected South African
adults with culture-confirmed pulmonary tuberculosis
[4-6]. Mycobacterial sputum culture, the de facto gold
standard diagnostic test, is not widely available in
resourcelimited settings due to its time- and laborintensive nature,
and is only available at 53% of health facilities in
subSaharan Africa [7,8]. The Xpert MTB/RIF assay is a
substantial advancement in tuberculosis diagnostics, but the
assays high costs, operator time, and reliance on electricity
may render it impractical at the clinical point-of-care in
many settings [9,10]. The World Health Organizations
Stop TB Department still identifies research and
development of novel diagnostics as a research priority [11,12].
Lipoarabinomannan (LAM), a lipopolysaccharide that
forms a major component of the cell wall of tuberculosis, is
released from metabolically active or degrading organisms,
and is filtered by the kidneys and excreted in urine . A
laboratory-based urine LAM ELISA test had varying levels
of test sensitivity, but high specificity, for detecting active
tuberculosis [4,14-17]. A lateral flow assay for urinary LAM
(Determine TB LAM; Alere, Waltham, USA) was
developed to return results in less than 30 minutes and without
reliance on laboratory equipment or reagents. We sought
to prospectively assess the diagnostic accuracy of the rapid
urine LAM test when used by trained nurses in a
clinicalsetting for tuberculosis screening among newly-diagnosed
Study sites and participants
We conducted a prospective clinic-based study of
newlydiagnosed HIV-infected adults who presented for voluntary
HIV counseling and testing from October 2010 to May
2011. Enrollment, specimen collection, and urine LAM
testing were conducted in outpatient clinical areas of
McCord Hospital, St. Marys Hospital, and two municipal
health clinics in KwaZulu-Natal, South Africa. McCord
Hospital is an urban, state-aided general hospital that serves
the greater Durban area. St. Marys Hospital in Mariannhill
is a state-aided general hospital that serves a
resourcelimited population in a peri-urban area of Durban. Both
McCord Hospital and St. Marys Hospital operate
highvolume outpatient HIV clinics that had been providing
ART since 2001 and 2003, respectively, and receiving
Presidents Emergency Plan for AIDS Relief (PEPFAR) support
since 2004. The two municipal primary health clinics,
Tshelimnyama and Mariannridge, are primary health care
clinics located within the catchment area of St. Marys
Hospital. Throughout the course of the study, all four
clinical sites offered free HIV counseling and rapid testing
during normal business hours.
We offered enrollment to adults (18 years) newly
diagnosed with HIV on the same day. We excluded those
already known to be HIV-infected, pregnant, or unwilling
to share their HIV test results with the research team. All
participants provided written informed consent either in
English or Zulu. The ethics committees of McCord
Hospital [IRB00005803] and St. Marys Hospital in
Durban, and Partners HealthCare in Boston [Protocol #:
2006-P-001379/40] approved the study.
Prior to study commencement, a representative from Alere
Inc. conducted a training session for 3 study nurses, each of
whom had previously received training in the diagnosis,
treatment, and care of tuberculosis-infected patients. The
training session reviewed the function, procedure, and
interpretation of the Determine TB LAM test (Alere Inc.,
Waltham, USA). Each nurse practiced performing and
interpreting the urine LAM test with direct supervision
from the representative, and became comfortable
conducting clinic-based urine LAM testing using the provided
reference scale card.
Upon enrollment, study nurses collected demographic
details, self-reported history of prior tuberculosis care and
treatment, signs and symptoms of tuberculosis using a
standardized questionnaire, and current use of diuretic
medications that may alter urine LAM results . Study
nurses obtained a respiratory sputum sample and a urine
specimen in a sterile container. Participants unable to
provide an expectorated respiratory sputum sample received
sputum induction with nebulized 3% hypertonic saline
using a portable machine (WH-802, Yuehua Medical
Instrument Factory Co.; Guangdong, China).
Study nurses performed urine LAM testing in
accordance with the manufacturers specifications at the clinical
point-of-care. LAM test results were not used to guide
therapeutic decisions. All LAM tests used were from
Manufacturer Lot Numbers 110512, 120215, or 120222.
The LAM test kits were maintained in a sealed pouch at
room temperature (15 26C), and always within the
manufacturers required range of 2 30C. All urine samples
were tested immediately after urine collection. If there was
an interruption in LAM test supply and the sample could
not be tested within 8 hours of specimen collection, urine
samples were stored in a 20C frost-free freezer (actual
temperature ranged from 18 to 22C). When frozen
urine samples were tested, each specimen was brought to
room temperature for at least one hour prior to testing,
and thawed samples were centrifuged at 10,000 G for
5 minutes at room temperature. For all tests, 60 microliters
of urine or clear supernatant was pipetted to the LAM test
strip, and the nurse from the respective clinic of the
participant interpreted test results.
Due to prior concerns of poor test sensitivity, each nurse
conducted two urine LAM tests on one urine sample from
each participant. One nurse at each site interpreted test
results within 2535 minutes, and recorded the time to
test result based on a portable timer, under ambient
lighting conditions. Participants were considered urine LAM
positive if either urine LAM test was positive by the
appearance of a color band, as defined by the manufacturer,
and tests were not scored. Nurses had access to a small
reference card supplied by the manufacturer. If either
urine LAM test result was not interpretable, the study
nurse repeated the test using the same urine sample. The
urine samples were then labeled and transported to a
laboratory at the University of KwaZulu-Natal for storage in
a -20C freezer.
Respiratory sputum samples were transported to a
reference laboratory at the University of KwaZulu-Natal for
smear microscopy (AFB) and mycobacterial culture.
Certified technologists at a reference laboratory performed
smear microscopy using both Ziehl-Neelsen and Auramine
stains. Before staining for AFB, sputum samples were
decontaminated with N-acetyl L Cysteine and NaOH to a
final concentration of 1.25% before being centrifuged at
3,000 revs for 20 minutes and resuspended in 1 ml of 7H9
broth. Sputum samples were inoculated onto Middlebrook
7H11 solid agar medium and 0.5 ml of sample were used
for liquid mycobacterial growth indicator (MGIT) tubes
(automated Bactec 960 instrument). Culture plates were
read at 3 and 6 weeks. We identified positive MGIT or solid
agar cultures as Mycobacterium tuberculosis using niacin
and nitrate testing, and all isolates from positive cultures
underwent drug susceptibility testing.
All participants were evaluated by a non-study clinician
as part of their usual care, offered CD4 count testing, and
received additional diagnostic evaluations, such as a chest
X-ray or abdominal ultrasound, when indicated. All HIV
testing, care, and treatment were provided in accordance
with current South African Department of Health HIV
testing and treatment guidelines . All participants were
followed for 9 months for assessment of anti-tubercular
We analyzed and reported the study results in accordance
with the STAndards for Reporting of Diagnostic accuracy
studies (STARD) . We excluded participants taking
anti-tubercular therapy at the time of LAM testing, as well
as those unable to produce a sputum or urine sample,
from all analyses. The AFB was recorded as positive if
either the Ziehl-Neelsen or Auramine stain was positive.
We compared urine LAM results to culture-confirmed
pulmonary tuberculosis, which we defined as positive
sputum culture for M. tuberculosis, the accepted gold standard.
Because mycobacterial culture is an imperfect gold
standard test for active tuberculosis , we also compared urine
LAM results to clinically suspected tuberculosis, which
we defined as having either culture-confirmed pulmonary
tuberculosis, a diagnosis of extrapulmonary tuberculosis,
or having been initiated on anti-tubercular therapy by a
The study population was characterized with simple
descriptive statistics. We calculated LAM test
sensitivity, specificity, likelihood ratios (positive and negative),
and predictive values for urine LAM and sputum AFB
for sputum culture-confirmed pulmonary tuberculosis.
We repeated the same analyses when using a combined
screening strategy with both urine LAM and sputum
AFB testing. For this combined analysis, a screening test
was considered positive if either the urine LAM or
sputum AFB results were positive. We conducted overall
analysis and also assessed LAM test accuracy
characteristics, stratified by CD4 cell count, and calculated exact
95% confidence intervals (CI) for estimates of prevalence
and diagnostic accuracy. We also evaluated the diagnostic
test performance characteristics of urine LAM using the
secondary outcome, clinically suspected tuberculosis. We
did not assess diagnostic accuracy of sputum AFB for
clinically suspected tuberculosis, since AFB test result
was used to guide anti-tubercular therapy initiation. We
assessed whether the primary or the secondary case
definition of tuberculosis were associated with gender, prior
tuberculosis infection, or diuretic use. Sensitivity and
specificity were defined as the true positive and true negative
rates, respectively. Likelihood ratio positive (and negative)
was the probability of a person who has the disease testing
positive (negative) divided by the probability of a person
who does not have the disease testing positive (negative).
We calculated the change in clinical pre-test probability,
by multiplying the pre-test odds by the positive or negative
likelihood ratio and then converting back to a post-test
probability, when using a combined screening strategy
with both urine LAM and sputum AFB testing. All
reported p-values were two-tailed, and a p-value <0.05 was
considered statistically significant. We conducted analyses
using SAS software (version 9.2; SAS Institute, Cary, NC).
Role of the funding source
The sponsor of the study had no role in study design,
data collection, data analysis, data interpretation or
writing of the manuscript. The corresponding and
senior authors had full access to all the data in the study
and had final responsibility for the decision to submit
Among the 411 newly-diagnosed HIV-infected adults
enrolled, 342 (83.2%) participants completed urine LAM and
sputum culture testing, and were not receiving
antitubercular therapy (Figure 1). Forty-five (13.2%) were urine
LAM positive, with an estimated population prevalence of
9.8-17.0%. Based on this sample, the estimated sputum
culture-positive tuberculosis prevalence was 17.5% (95% CI
13.7-22.0%). The mean age was 35.6 years (S.D. 9.8 years),
and 190 (55.6%) participants were male (Table 1).
Twenty-nine (8.5%) participants reported a history of
previous tuberculosis disease. Three (0.9%)
participants were taking diuretic medications at the time of
LAM testing. Two hundred-eighty (81.9%) underwent
CD4 testing; the median CD4 cell count was 182/mm3
(IQR 70-298/mm3). Among the entire cohort, 44 people
(11%) were unable to provide an expectorated or induced
sputum sample, while 13 people (3%) were unable to
provide a urine sample.
Among this cohort, 24 (7.0%) participants were
sputum smear microscopy (AFB) positive, with an
estimated population prevalence of 4.6-10.3%. Sixty-three
(18.4%) participants had either a positive sputum AFB
or urine LAM test, with an estimated population
prevalence of 14.5-22.9% (Table 1). Among urine LAM
positive participants, 36 (80.0%) had two positive urine
LAM tests, and 9 (20.0%) had one positive urine LAM
test. We performed urine LAM testing on the same day
as specimen collection for 294 (86.0%) participants. We
performed urine LAM testing on frozen samples for 48
(14.0%) participants, as a result of an interruption in
LAM test supply. Among the samples tested in the
clinic, the mean time from urine specimen collection to
obtaining a LAM test result was 40.0 minutes (95% CI
Figure 1 Participant flow diagram.
Mean S.D. or N (%)
Received treatment for prior TB
CD4 cell count (median/IQR)/mm3*
Sputum smear microscopy (AFB) positive
Sputum AFB or urine LAM positive
Culture-confirmed pulmonary TB
*N = 280.
Diagnostic accuracy of LAM for culture-confirmed
Urine LAM test estimated sensitivity and specificity
for diagnosing culture-confirmed pulmonary
tuberculosis were 28.3% (95% CI 17.5-41.4%) and 90.1% (95%
CI 86.0-93.3%), respectively (Table 2). Urine LAM test
Table 2 Diagnostic accuracy of urine LAM and/or sputum smear microscopy (AFB) testing for culture-confirmed
CD4 100 cells/mm3
CD4 < 100 cells/mm3
CD4 100 cells/mm3
CD4 < 100 cells/mm3
CD4 100 cells/mm3
CD4 < 100 cells/mm3
17/60 28.3 (17.5-41.4) 254/282 90.1 (86.0-93.3) 2.85 (1.67-4.87)
0.80 (0.68-0.94) 37.8 (23.8-53.5) 85.5 (81.0-89.3)
25.0 (9.0-49.0) 153/167 91.6 (86.3-95.3) 2.98 (1.20-7.41)
26.3 (9.0-51.2) 91.1 (85.7-94.9)
12/32 37.5 (21.1-56.3)
86.9 (75.8-94.2) 2.86 (1.30-6.27)
0.72 (0.54-0.96) 60.0 (36.1-80.9) 72.6 (60.9-82.4)
18.3 (9.5-30.4) 269/282 95.4 (92.3-97.5) 3.98 (1.87-8.44)
0.86 (0.76-0.97) 45.8 (25.6-67.2) 85.6 (80.2-88.4)
20.0 (5.7-43.7) 158/167 94.6 (90.0-97.5) 3.68 (1.25-10.89) 0.85 (0.68-1.06)
30.8 (9.0-61.4) 90.8 (85.4-94.6)
98.4 (91.2-99.9) 7.63 (0.89-65.40) 0.89 (0.78-1.02) 80.0 (28.4-99.5) 68.2 (57.4-77.7)
23/60 38.3 (26.0-51.8) 242/282 85.8 (81.1-89.7) 2.70 (1.76-4.16)
0.72 (0.59-0.88) 36.5 (24.7-49.6) 86.7 (82.2-90.5)
35.0 (15.4-59.2) 145/167 86.8 (80.6-91.5) 2.64 (1.29-5.39)
0.75 (0.54-1.04) 24.1 (10.3-43.5) 91.7 (86.3-95.5)
13/32 40.6 (23.7-59.4)
85.3 (73.8-93.0) 2.75 (1.32-5.74)
0.70 (0.51-0.94) 59.1 (36.4-79.3) 73.2 (61.4-83.1)
*Test considered positive if either Urine LAM or sputum AFB were positive.
LR = likelihood ratio; PV = predictive value; CI = confidence interval.
sensitivity was 37.5% (95% CI 21.1-56.3%) for those
with CD4 cell count <100/mm3, which did not differ
significantly from those with a CD4 count > l00/mm3
(sensitivity =25.0%, 95% CI 9.0-49.0%; p = 0.38). In
addition, a test for trend did not find significantly
greater sensitivity at lower CD4 count strata (p = 0.46).
Estimated test sensitivity and specificity for sputum
AFB were 18.3% (95% CI 9.5-30.4%) and 95.4% (95% CI
92.3-97.5%), respectively. The urine LAM test identified
10% more cases of culture-positive pulmonary
tuberculosis than sputum AFB. Likelihood ratio (LR) positive and
LR negative values for urinary LAM testing were 2.85
(95% CI - 1.67-4.87) and 0.80 (95% CI - 0.68-0.94),
respectively. The LR positive and negative for sputum AFB
were 3.98 (95% CI 1.87-8.44) and 0.86 (95% CI 0.76-0.97),
respectively. Among the 9 LAM discordant results, 2
people were culture-positive for tuberculosis and 1
additional person was clinically suspected of having active
tuberculosis. There were no significant differences in
baseline characteristics or urine LAM test results among the
48 frozen urine samples compared to those with a fresh
urine sample, or participants without a CD4 result
compared to those with a CD4 result.
When using a combined screening strategy of either urine
LAM or sputum AFB positive, test sensitivity and specificity
were 38.3% (95% CI 26.0-51.8%) and 85.8% (95% CI
81.189.7%). The addition of urine LAM to sputum AFB
testing detected an additional 20% of culture-positive
pulmonary tuberculosis cases, which was a statistically
significant improvement (p = 0.02). With this combined
screening strategy, the LR positive and negative values
were 2.70 (95% CI 1.76-4.16) and 0.72 (95% CI 0.59-0.88).
Diagnostic accuracy of LAM for clinically suspected
Within our cohort, 92 (26.9%) participants met our
definition of clinically suspected tuberculosis, which
gives an estimated population prevalence of
22.331.9%. Nine (2.6%) participants were diagnosed with
extrapulmonary TB, which gives an estimated
population prevalence of 1.2-4.9%. Among those 32
participants started on therapy with a negative sputum
culture, 9 (28.1%) had positive AFB testing, 6 (18.8%)
were diagnosed with extrapulmonary tuberculosis, and
16 (50.0%) were diagnosed based on clinical signs,
symptoms, and/or chest radiography. In addition, 1
(3.1%) participant was diagnosed as sputum
culturepositive on a sputum sample sent through the hospitals
clinical laboratory, and was started on anti-tubercular
therapy, but the sputum culture at our reference
laboratory remained negative.
We assessed diagnostic performance characteristics of
the urine LAM test using our secondary case definition of
clinically-suspected active tuberculosis (Table 3). In these
analyses, urine LAM test sensitivity and specificity were
25.0% (95% CI - 16.6-35.1%) and 91.2% (95% CI -
87.094.4%), respectively. The LR positive and negative were
2.84 (95% CI - 1.67-4.48) and 0.82 (95% CI - 0.73-0.93).
These results were almost identical to the
cultureconfirmed pulmonary tuberculosis, and CD4 strata had
little impact on test characteristics. In addition,
diagnostic accuracy of the urine LAM test was not
associated with gender, prior tuberculosis infection, or
diuretic use for both culture-confirmed and clinical
Table 3 Diagnostic accuracy of urine LAM testing for clinically suspected active tuberculosis
CD4 100 cells/mm3
CD4 < 100 cells/mm3
LR = likelihood ratio; PV = predictive value; CI = confidence interval.
Comparison between sputum AFB and urine LAM testing
Among the 24 sputum AFB positive participants, 6
(25%) were urine LAM positive and 18 (75%) were urine
LAM negative. Among the 60 participants with
cultureconfirmed pulmonary tuberculosis, urine LAM testing
identified 12 (20%) participants more than sputum AFB,
and sputum AFB testing identified 6 (10%) participants
more than urine LAM (Figure 2a). Only 5 of 60 (8%)
sputum culture-positive participants were identified by
both sputum AFB and urine LAM testing.
Among the 92 participants with clinically suspected
tuberculosis, urine LAM testing identified 17 (18%)
participants more than sputum AFB, and sputum AFB testing
identified 11 (12%) participants more than urine LAM
(Figure 2b). Only 6 of 92 (7%) participants with clinically
suspected tuberculosis were identified by both sputum
AFB and urine LAM testing.
Post-test Probability of Tuberculosis
A representation of post-test probability of tuberculosis
when using a combined screening strategy of sputum
AFB and urine LAM testing is shown in Figure 3. If the
baseline prevalence of tuberculosis is 10% (column A),
negative sputum AFB and urine LAM decreased the
post-test probability to 7.4%, while either positive test
increased the post-test probability to 23.1%. When assuming
a prevalence of tuberculosis of 17.5% (column B), as
observed for culture-positive pulmonary tuberculosis in our
cohort, positive sputum AFB or urine LAM increased
post-test probability to 36.4%. When assuming a
prevalence of tuberculosis of 26.9% (column C), as observed for
clinically suspected tuberculosis in our cohort, positive
sputum AFB or urine LAM increased post-test probability
to 49.8%. When assuming a higher pre-test probability of
tuberculosis (40%; column D), negative sputum AFB and
urine LAM decreased the post-test probability of
tuberculosis to 32.4%, while either positive test increased post-test
probability to 64.3%.
In this prospective, clinic-based study, the Determine
TB LAM urine test had low sensitivity, or a high false
negative rate, as a screening test for tuberculosis among
newly-diagnosed HIV-infected adults in a
tuberculosisFigure 2 Urine LAM and sputum smear microscopy (AFB)
to diagnose tuberculosis among those who were either
culture-confirmed (Figure 2a) or diagnosed with clinically
suspected (Figure 2b) tuberculosis. a. Culture-confirmed
Pulmonary Tuberculosis (N = 60). b. Clinically Suspected Tuberculosis
(N = 92). Any participant who were LAM + but not diagnosed with
culture-confirmed or clinically suspected tuberculosis are not
depicted in these figures.
Figure 3 Post-test probability of tuberculosis when using a combined screening strategy of sputum AFB and urine LAM testing for
various pre-test probabilities. Column A represents a cohort with 10% prevalence of tuberculosis; columns B and C represent the baseline
prevalence of culture-positive pulmonary tuberculosis (17.5%) and clinically suspected tuberculosis (26.9%) that we observed in our cohort. Column D
represents a cohort with a 40% prevalence of tuberculosis, which might occur among tuberculosis suspects in a highly endemic region.
endemic region. However, the urine LAM test had
comparable test sensitivity to sputum AFB, and, when
combined with sputum AFB testing, added 20% to the true
positive rate, though at the expense of identifying an
additional 9.6% as false positives. Urine LAM testing
was easily performed by trained nurses in an outpatient
clinic, returned results within an hour of sample
collection, and did not require electricity, reagents, specimen
transport, or a highly-trained laboratory microscopist.
Our data support a recent suggestion that the urine
LAM test be used in conjunction with, and not in place
of, current diagnostic tests for active tuberculosis .
Diagnostic accuracy of the Determine TB LAM test
has been reported in laboratory- and hospital-based
studies. In a retrospective, laboratory-based study using frozen
urine samples, Lawn et al. found nearly identical test
sensitivity (28.2%) for detecting culture-positive pulmonary
tuberculosis, but a higher test specificity (98.6%), when
using urine LAM as a screening test among HIV-infected
adults in Cape Town . Their higher test sensitivity
may be a result of performing two sputum cultures for
most (94.6%) participants, as well as performing urine
LAM testing on frozen samples in a controlled
laboratoryenvironment. In a study of HIV-infected TB suspects, 34%
of whom were receiving antiretroviral therapy, a urine
LAM testing had a sensitivity of 44.8% and specificity of
90.1% . While the test specificity was similar to our
findings, the higher test sensitivity was likely due to
inclusion of patients with higher bacillary loads, as 34% of their
participants had mycobacterium detected in blood
cultures, as well as sicker hospitalized patients. We
performed 2 urine LAM tests per sample, which improved
sensitivity, but reduced overall test specificity. A second
study of hospitalized HIV-infected patients reported test
specificity of 90% when using the manufacturers threshold
of positive versus negative, which was similar to our
findings . In contrast to these study, our results
represent diagnostic accuracy when trained nurses use
Determine TB LAM testing as a screening test in
newlydiagnosed HIV-infected adults in a real-world outpatient
clinical setting, where patients generally have less
advanced disease compared to hospitalized patients.
Although the rapid urine LAM test was comparable to
sputum AFB for detecting active tuberculosis, when
combined the two tests improved detection of tuberculosis. In
a retrospective study by Lawn et al., adding urine LAM
testing to sputum AFB testing increased overall sensitivity
from 28.2% to 43.5%, while having minimal impact on test
specificity . While the change in sensitivity was similar
to our study results, we found a large decrease in test
specificity, or a higher false negative rate. Other studies have
found the laboratory-based ELISA urinary LAM test
capable of detecting extra-pulmonary tuberculosis . The
addition of urine LAM to existing screening strategies
would be relatively inexpensive, and the rapid urine LAM
test has been reported to be cost-effective when used to
diagnose HIV-infected adults with CD4 < 100/mm3 and
symptoms of tuberculosis . In our cohort, urine LAM
detected one-third of participants with extrapulmonary
TB. The price for one LAM test, including a disposable
pipette, was US $3.05, or $6.10 for our two-test screening
Utilizing rapid urine testing for active tuberculosis is
appealing for several reasons. First, as we demonstrated in
this study, the Determine TB LAM urine test is a true
clinic-based, point-of-care test that can be used by trained
nurses in peripheral clinics or remote settings without
electricity or reliance on laboratory infrastructure. Second,
participants were 3 times more likely to produce a urine
sample than a sputum sample, which has been similarly
reported in another study . This difference could have
additional clinical benefit for urine LAM testing, but would
need to be evaluated in an operational study . Third,
obtaining urine samples from tuberculosis-infected patients
carries a lower risk of transmission to health care workers
than sputum specimens containing live, active bacilli.
Finally, urine LAM has the potential for detection of
extrapulmonary tuberculosis and may be a valuable biomarker
of tuberculosis resolution during anti-tubercular therapy.
Our study had several limitations and strengths.
Trained nurses performed specimen collection and urine
LAM testing in an outpatient clinic to assess diagnostic
accuracy when used at the clinical, not hospital,
pointof-care in a real-world setting. While trained nurses may
not interpret test results as accurately as a certified
laboratory technicians, these results are more consistent
with the intended use of the rapid, point-of-care test. If
nurses had interpreted the appearance of a weak, faint
test line as positive, this could have resulted in reduced
test specificity. We obtained one sputum sample for the
gold standard test of mycobacterial culture, while some
studies of diagnostic accuracy included two or three
specimens [23,24]. Sputum culture is an imperfect gold
standard test and non-differential misclassification could
lead to reduced diagnostic accuracy. We did not perform
Xpert MTB/RIF testing, obtain mycobacterial blood
cultures, perform testing on those unwilling to share their
HIV status, score the positive urine LAM tests, obtain
user performance evaluation data, obtain data on clinical
reasons for initiating TB treatment, evaluate causes of
extrapulmonary tuberculosis, measure inter-observer
variability, or measure the bacillary burden of tuberculosis.
Finally, we evaluated urine LAM as an outpatient screening
test among HIV-infected adults with and without
tuberculosis symptoms in a tuberculosis-endemic region, and these
results may not be generalizable to other populations or
areas with low tuberculosis rates.
In conclusion, although a generalized role for urine LAM
testing may be limited by poor test sensitivity, the rapid
urine LAM test added important diagnostic case detection
when combined with sputum AFB as a screening test for
tuberculosis among newly-diagnosed HIV-infected adults
in a tuberculosis-endemic region. In the absence of a
highly accurate clinic-based, point-of-care test for active
tuberculosis, clinic-based urine LAM testing offers a rapid,
inexpensive option with diagnostic yield that is similar,
but complementary, to sputum smear microscopy. Urine
LAM testing may be beneficial in settings with limited
capacity for sputum smear microscopy or when a timely
diagnosis of TB is paramount, but would greatly benefit by
yielding a higher test sensitivity. Since urine LAM testing
has several appealing point-of-care properties, clinical
studies are warranted to determine whether urine LAM
testing influences patient outcomes.
We declare that we have no conflicts of interest.
PKD, EL, and IVB designed the study. PKD, SMC, JG, DR, and IVB collected
and assembled data. EL and SMC performed statistical analysis. PKD wrote
the report with input from EL, SMC, JG, DR, JNK, RPW, KAF, and IVB. All
authors approved the final version of the article.
We would like to acknowledge the excellent work and valuable
contributions of our research staff and nurses. We thank each of the clinical
sites for sharing their enthusiasm and space. Finally, we graciously thank all
of the men and women who participated in this study.
This research was supported by the Harvard Global Health Institute, the
Fogarty International Clinical Research Scholars and Fellows Program at
Vanderbilt University (R24 TW007988), The Program in AIDS Clinical Research
Training Grant (T32 AI007433) (PKD); the National Institute of Mental Health
R01 MH090326 (IVB) and R01 MH073445 (RPW); the National Institute of
Allergy and Infectious Disease R01 AI058736 (KAF); the Harvard University
Center for AIDS Research P30 AI060354; the National Institute of Arthritis and
Musculoskeletal and Skin Diseases K24 AR057827 (EL); the National Center for
Research Resources (the Harvard Catalyst UL1 RR 025758); and the Claflin
Distinguished Scholar Award (IVB).
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