oCtoBeR 2010 - American Association for Clinical Chemistry

detecting il-2 and ifn-γ
discriminates between active
and latent Tb infection
new research indicates that detecting
interleukin-2 (IL-2) in addition
to interferon-γ (IFN-γ) discriminates active
from latent Mycobacterium tuberculosis
infection (Clin Microbiol Infect
2010;16:1282-1284). The research builds
diagNostiC
22 CliniCal laboratory news oCtoBeR 2010
p r o f i L e s
p r o f i L e s
on recent studies demonstrating the utility
of assays that measure IFN-γ release in
blood cells stimulated with M. tuberculosis
antigens, according to the authors. IFN-γ
release assays accurately diagnose tuberculosis
(TB) infection, but do discriminate active
from latent TB.
The researchers stimulated whole blood
with M. tuberculosis-specific antigens and
used the QuantiFERON-TB Gold In Tube
test to measure IFN-γ release and a commercially
available ELISA assay to measure
IL-2 release after 18 and 72 hours of incubation.
The specimens came from patients
hospitalized in an infectious diseases unit
and from control subjects without known
exposure to TB. Participants also underwent
tuberculin skin testing (TST); those
with positive test results and positive M.
tuberculosis culture from sputum were considered
to have active TB. Latent infection
was defined as positive tests in exposed individuals
with no signs of active disease.
The investigators found that subjects
with either latent or active TB had significantly
higher levels of IFN-γ than controls.
However, IFN-γ levels between individuals
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with latent or active TB were not significantly
different at 18 or 72 hours after incubation.
In contrast, after 72 hours’ incubation,
IL-2 levels were significantly higher
in patients with latent TB infection than either
active TB or healthy controls. The area
under the receiver operator characteristic
curve was 0.99, and a threshold of 2.0 U/
mL yielded a sensitivity of 90% and specificity
of 97.5%.
The authors speculate that the increased
levels of IL-2 observed in latent TB infection
likely reflect more IL-2 secreting and
IL-2/IFN-γ-secreting central memory Tcells
along with fewer IFN-γ-secreting effector
memory T-cells in individuals with
latent as opposed to active TB.
bnp levels do not predict
intracranial hemorrhage in
pediatric Trauma patients
researchers at Children’s Hospital Los
Angeles found that B-type natriuretic
peptide (BNP) levels measured during an
emergency visit do not predict intracranial
hemorrhage (ICH) in pediatric trauma
patients (J Trauma 2010;68:1401–5). They
conducted the study to determine whether
BNP might help identify children most in
need of computed tomography (CT) scans.
Emerging evidence indicates there is a significantly
increased risk of cancer among
pediatric patients who have CTs, and protocols
to deploy CT more selectively have
been implemented. At the same time,
emerging evidence suggests that BNP levels
are elevated in adults with head injuries.
Since BNP tests are readily available and
can be performed quickly, the researchers
hypothesized that this analyte might predict
ICH and help guide physicians in determining
whether a CT would be needed.
They enrolled 100 consecutive pediatric
patients presenting at the emergency
department who were classified as Level I
trauma status with the most critical injuries
and physiologic parameters. However,
of 95 patients who remained in the study
for analysis, they did not find a relationship
between BNP levels and the presence
of various trauma injury measurements
such as injury severity score, Glasgow coma
scale, or loss of consciousness. In fact, BNP
levels for 57.9% of patients were below the
assay’s lower limit of detection, and mean
BNP levels among patients in the positive
ICH group were slightly less than those
who were negative for ICH.
While the researchers conclude that
based on their study, BNP levels are not
clinically relevant to predict CTs with positive
results for ICH, they underscored that
specimens drawn for the study were taken
only upon arrival at the emergency department.
However, evidence in adults indicates
that BNP levels in aneurysm and subarachnoid
hemorrhage did not rise significantly
until hours or days later. The authors suggest
that further investigation of pediatric
BNP levels outside the emergency setting is
warranted.
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