Download The Use of the Unstimulated Nitroblue Tetra

The Use of the Unstimulated Nitroblue Tetrazolium Test as a Routine Screening Test for
Bacterial Infection in an Adult Population:
A Reassessment
STEPHEN J. BITTNER, M.D., ELLIOTT K I E F F , M.D.,
DOROTHY WINDHORST,
M.D.,
AND PAUL MEIER, P H . D .
University of Chicago, Departments of Medicine and Statistics, Chicago, Illinois
ABSTRACT
Bittner, Stephen J., Kieff, Elliott, Windhorst, Dorothy, and Meier, Paul:
The use of the unstimulated nitroblue tetrazolium test as a routine screening
test for bacterial infection in an adult population: A reassessment. Am. J. Clin.
Pathol. 60: 843-853, 1973. A simplified version of the unstimulated nitroblue
tetrazolium (NBT) test potentially adaptable for routine general hospital use
was devised and employed to study 141 subjects in four population groups:
healthy adults, patients with bacterial infection, patients with nonbacterial
infection, and patients with noninfectious illness. There was no distinct
segregation of patients with bacterial infections from patients with other
disease processes. The NBT test failed to correlate with the underlying
diagnosis in 27% of the subjects studied. T h e method of Park et al16 was
employed simultaneously in 45 subjects and the two methods were found
to have comparable accuracy of discrimination. T h e NBT test was also
compared with erythrocyte sedimentation rate, pyrexia, and neutrophilia
as indices for discriminating bacterial infection from other disease and found
to be the least discriminatory single test. T h e unstimulated NBT test may be
somewhat useful as an adjunct to other indices in diagnosing bacterial
infection, but it is not appropriate for the routine laboratories of acute
general hospitals.
PARK ET AL.16
first demonstrated that the
mean proportion of neutrophils capable
of spontaneous reduction of nitroblue
Received April 9, 1973; received revised manuscript June 1, 1973; accepted for publication June
4, 1973.
Supported in part by U. S. Public Health Training
Grant 1 T01 AI00449-01 from NIAID.
Presented in part at the November 1, 1972 meeting
of the Central Society for Clinical Research.
Address reprint requests to: Dr. Elliott Kieff,
Department of Medicine, Pritzker School of Medicine,
University of Chicago, Chicago, Illinois 60637.
843
tetrazolium dye in vitro was significantly
elevated in 25 pediatric patients with acute
bacterial infection and four with candidemia. T h e test clearly differentiated these
from 30 healthy controls and 65 patients
with other disease processes: rheumatoid
arthritis, systemic lupus erythematosus,
viral infections, mumps encephalitis, and
primary tuberculosis. Since the initial
study, prospective and retrospective series
have found it to be useful as an adjunct to
844
A.J.C.P.—Vol. 60
BITTNER ET AL.
Table 1. Patient Population Studied and Test Values
Condition
I. Bacterial infections
UTI with bacteremia
UTI without bacteremia
Pneumonia
No. of
Subjects
No. of
Tests
5
3
5
3
15
16
%NBT©PMN
8.5 13 13 3.75
4 12.25 5.25
6 0.25 9.25 2.5 7 3 1.75 42
10.25 22.5 6.5 0.5 19.5 10.25
10.25 15
Carcinomatosis with bacteremia
5
5
1
Intra-abdominal abscess
4
4
10.5
Osteomyelitis
2
2
12
Septic abortion
2
2
2.75
20
Suppurating leg ulcers
2
2
18.5
10.5
Intracranial abscess, endometritis, septic
thrombophlebitis, lung abscess, tertiary
syphilis, gastroenteritis secondary to
post-antibiotic overgrowth
1 each
(6)
9.25
0.75
0
3.75
0
0.75
12
13
0.5
1 each 32.25
(6)
16
53.5
4.5
Meningitis
3
3
5.5
Bacterial endocarditis
4
4
33.5
51
52
Infectious mononucleosis
Herpes zoster
Guillain-Barre syndrome
Viral URI
Viral gastroenteritis
Aseptic meningitis
Infectious hepatitis
1
2
2
2
1
1
1
2
2
2
2
Pneumocystis carinii pneumonia
1
5.25
Active pulmonary tuberculosis
1
7
Malaria
1
7.75
Systemic candidosis
1
2
Chronic mucocutaneous candidosis
1
2
15
17
5
7
7
Rule out immune deficiency
3
4
Psoriasis
5
5
Rheumatoid arthritis
4
4
0.5
Carcinomatosis
3
3
1
4.5
Systemic lupus erythematosus
3
3
7
7
Profound nutritional anemia
2
2
0
2.5
2
2
17
2.5
1.25
26
9.5
11.5
3.25
0.75
13.5
64
Non-bacterial infections
Viral:
III. Noninfectious illnesses
Ulcerative colitis
Fibrinous pericarditis
Asthmatic attack
Thrombophlebitis
1 each
(24)
7 4
2.5 2.75
4 3.75
7.5 7.5
1
1.75
2.75
4.5
7
6.25
21
3.5
12
4.5
8
6.5
2.5
1
12.5
1 each 9
(24) 7.5
1.5
4.5 3.5
17
6.5
1
4.25
1.75
16.75
December 1973
845
UNSTIMULATED NBT TEST
Table
Condition
1.—(Continued)
No. of
Subjects
No. of
Tests
%NBT0PMN
2.5
Cerebrovascular accident
Disseminated intravascular coagulation
2° to ruptured ectopic pregnancy
Congestive heart failure
Sarcoidosis
Erythema nodosum
Idiopathic thrombocytopenia
Penicillin drug reaction
Transfusion reaction
Myasthenia gravis
Mycosis fungoides
Eczema
Polymyalgia rheumatica
Scrotal dermatitis—aseptic
Allergic granulomatous vasculitis
Sickle-cell anemia crisis
Pleural effusion—aseptic
Brown-Sequard syndrome
Leg ulcer
Osteomalcia—vitamin D deficiency
Galactorrhea—? etiology
Cholelithiasis
Hypothyroidism
4
5.25
6.5
4.75
0.25
64
10
2.25
0.5
1.5
8.5
0
39.5
0
6
1
11.25
2
0
2.5
0.5
51
54
IV. Normal controls
24
29
the differentiation of bacterial infection from other febrile conditions and
infections in adults as well as children. 6 " 1 0 1 2 1 3 1 8 2 1 In the one evaluation
of the test in a large adult series, 12 94% of
the subjects with bacterial infection had
elevated proportions of NBT-positive neutrophils (NBTSPMN's), while in a group
of 18 controls and 84 patients with nonbacterial illness all but one had normal
NBT tests. As the result of this and other
studies, the NBT test has been recommended as a routine test for general service
laboratories. 11
There have, however, been many procedural modifications of the original test,
and the extent to which these modifications
affect the reliability of the test has not
been determined in comparative studies.
Furthermore, there is a growing number
of clinical situations in which the results
of the NBT test are not concordant with
the underlying diagnosis, and many of the
affirmative studies exaggerate the discriminatory ability of the test.6,8-21
We report here the results of a study
of the usefulness of the NBT test in deciding whether moderately to severely ill
adult patients admitted to an acute general
hospital have bacterial infection. Several
modifications of the Park method were
employed in an attempt to make the test
more adaptable to a routine clinical laboratory, and the reliability of the present
method was compared with that of the
Park method.
See histograms
Methods
One hundred and fifty-two tests were
carried out on 141 subjects, of whom 24
were healthy adult controls; 51 were consecutive patients with untreated bacterial
infections that were documented either
846
A.J.C.P. —Vol. 60
BITTNER ET AL.
before or after the NBT test was done;
15 were consecutive patients with nonbacterial infectious processes: viral, mycotic, mycobacterial or parasitic; 51 were
patients admitted to the University of
Chicago Hospitals with noninfectious diseases, most of whom were acutely ill (Table
1). Acute bacterial infections were documented by positive cultures of blood, urine,
sputum, spinal fluid or pus from patients
with appropriate clinical pictures.
In an attempt to adapt the NBT test
to a routine clinical laboratory, the Park
procedure 1 6 was modified as follows: 2 to
5 ml. of venous blood were collected in
8-ml. heparinized Vacutainer tubes (Becton-Dickinson). Within 40 minutes of
venipuncture, 0.8 ml. of blood was pipetted
into sterile polypropylene disposable tubes
(Falcon), and to this was added 0.2 ml of
0.02% nitroblue tetrazolium dye (Sigma)
in physiologic saline solution. The mixture
was incubated at 37 C. for 30 minutes
with continuous mixing on an oscillating
device. Cover-slip smears were then made
immediately, quickly air-dried, counterstained with Safranin O in 40% glycerin
for 4 minutes, and mounted on glass
slides with Permount (Fisher). All data are
given as % cells showing dye reduction
in 200 neutrophils counted under 400 X
power; the criteria for the determination
of the presence of reduced dye in cells
were those of Matula and Paterson. 12 Except for the heparinized tubes, plastic
tubes and pipettes were used throughout
to avoid stimulation of the leukocytes by
glass. Each sample was tested with simultaneous duplicates.
All determinations of NBTffiPMN's were
read blindly by a single observer.
In forty-five subjects the NBT©PMN's
were determined by both the Park method
and the above procedure. T h e only alteration in the use of the Park method was
to counterstain the cover-slip smears with
Safranin O instead of Wright's stain. Four
separate tests were done simultaneously
in the subgroup, two with each method.
Park method slides were coded and read
with the slides from the larger series.
Leukocyte count, differential, and sedimentation rate (Wintrobe method) were
performed on the same day for 103 of
the 152 test samples by regular technicians
in the hospital general service laboratory.
Results
Figure 1 shows the results of the 152
tests in the four clinical categories. For the
purposes of the between-population analyses, duplicate tests on single patients were
deleted; the 141 original tests on 141
patients were analyzed. T h e healthy adult
control population had a mean NBT©PMN count of 4.6%, with a standard
error of 4.3%; patients with bacterial infection had a mean count of 11.3% (SE
13.4%); patients with nonbacterial infection had a mean count of 4.4% (SE 2.4%);
patients with noninfectious illness had a
mean count of 7.1% (SE 10.6%). Eight
per cent N B T 0 P M N was arbitrarily selected as the boundary between normal
and elevated because it resulted in the
best concordance of NBT test results with
clinical diagnosis, i.e., the least number
of false positives plus false negatives. Fiftytwo per cent of tests on patients with bacterial infection were "abnormal," 28% of
tests on patients with noninfectious illness
were "abnormal," no test on any patient
with non-bacterial infection was "abnormal," 14% of tests done on normal
controls were "abnormal."
As can be seen from Figure 1, there
is a great deal of overlap in all four groups.
T h e NBT test does not appear to be an
effective discriminator between bacterial
and other illnesses. There are, however,
some average differences between groups
which are statistically significant. In particular, the average NBTffiPMN count for
the group with bacterial infections is
significantly higher than the average counts
for the population with non-bacterial infec-
December 1973
847
UNSTIMULATED NBT TEST
don and the normal controls (p < .05).
It is not significantly different, however,
from the average of the population With
noninfectious illness (p < 0.07). (In view
of the skewness of the distributions, a
square-root transformation was employed
with the hope that it would provide
clearer discrimination between the groups.
However, the results of the analysis of
the transformed values were the same as
those just stated).
In 45 subjects the Park method was
directly compared with our modification
(see Fig. 2). The healthy adult control
population had a mean NBTffiPMN count
of 20.9% (SE 13.8%). Patients with bacterial
infection had a mean value of 36.4%
(SE 13.2%). Three patients with non-bacterial infection had a mean value of 17.8%
(SE 9.8%). Patients with noninfectious illness had a mean value of 2 3 . 1 % (SE
13.8%). In comparing the reliability of
the two methods, we arbitrarily chose
24% as the upper limit of normal for the
Park method because that boundary resulted in the best possible correlation of
NBT result with clinical diagnosis. Both
methods conflicted with the underlying
diagnosis in 24% of the 45 patients in whom
the two methods were compared. As with
the data derived using the modified
method employed for the present study,
the differences between population means
were significant when patients with bacterial infection were compared with patients with non-bacterial infection (p
< 0.005) and with controls (p < 0.01).
Comparison of average test results in the
patient populations with bacterial infection
and noninfectious illness indicated significant differences for both test methods
in this subgroup of 28 patients. The results after transformation by square-root
analysis were again identical to the above.
Graphs A, B, C, and D in Figure 3
compare the results of the first blindlyread test (abscissa) and the second (ordinate) for each sample done with the present
70
r
60
50
z
f 40
©
Im
30
20
I
10
:«:•
„
B
.
°c,e.n<"
l
ln,ec,lon
t*
NonNonBocterml Infectious
Infection
Illness
54
..
Nor mtl
,
r.
Con,rols
n
52
X
11.3
4.4
7.1
4.6
SE
13.4
2.4
10.6
4.3
17
29
FIG. 1. NBT test results in 152 tests on 141 patients
in 4 clinical categories.
method, and Graphs E, F and G do likewise for samples done with the Park
method. (The population of patients with
non-bacterial infections in whom the Park
method was done was not included in this
analysis because of its small size). For the
present method the standard deviation
of the laboratory error as estimated from
duplicate determinations in each of the
152 samples is 3.5, and each of the four
clinical categories by itself has a comparable
value. For the Park method the standard
deviation of the laboratory error as estimated from duplicate determinations of
the 42 samples is 8.8, and each of the
3 clinical categories analyzed was a comparable value. The laboratory error for
both methods is thus fairly large compared with the differences between the
mean N B T 0 P M N counts for each clinical
A.J.C.P.—Vol. 60
BITTNER ET AL.
848
70
•
60 •
:
50
•
i
z
1 40 -
©
•
'•
#
I 30
Present method (#1)
Park M e t h o d ! * 2 )
Compared in 4 5
patients in the 4
specified clinical
categories The
arbitrary c u t - o f f
points ( 8 % forrfM
and 2 4 % for # 2 )
are shown as dotted
lines.
•
##
•
•
'
. 1
FIG.
2. Comparison of present method
and Park method.
20 :
1
'•
t
10
!
I
•
•
:
J
•i
Nc
Bacter al „ „ „ . . „ . , „ , „ , „ . . .
. . ..
Hooter al Infect ous
.Illness
..„,.
Infection I. n„ f,e„c,t i o_n„
1
1
2
2
:
:
.:
.
!:
Normal
...iControls
r
1
'2F©
3F© = I I Misdiagnoses
IF©
5F©
5F0I
OF©
3F©
3F©
= 11 Misdiagnoses
x
15.2 36.4
3.9
SE
16.3 Il3.2
1.6
17.8
7.2 23.1
9.8 10.4 13.8
5.2 20.9
5.4 13.8
category, and repeat tests would have given
opposite results in 29% of the samples
done with the present method and 12%
of those done with the Park method if
the respective arbitrary cut-off points of
8% and 24% had been employed.
Graphs H, I and J in Figure 3 demonstrate the variability between the two test
methods on the same subject. (The population of non-bacterial infection is again
omitted because of its small size.) T h e
line indicates the regression of the Park
method on the present method in the
42 subjects in which the two methods were
done simultaneously. It is clear that there
is little agreement between the two test
methods and that the extent of the disagreement is greater than can be accounted
for by the laboratory error alone.
In an attempt to determine the extent
to which other readily available measures
of inflammation might be combined with
the NBT test to increase the ability of the
test to predict bacterial infection, erythrocyte
sedimentation
rate
(Wintrobe
method), neutrophil count, and temperature were determined simultaneously in
103 subjects. ESR's ^ 50 mm/hr., absolute
neutrophil counts ;> 9,000 cells/mm. 3 , and
temperatures ^ 37.7 C. were arbitrarily
designated "abnormal" (see Table 2). One
of the 36 patients with noninfectious illness, a woman with polymyalgia rheumatica, had all four indices positive, and
only 7 of 44 bacterially infected patients
had all four acute-phase indices positive.
Conversely, one patient with bacterial infection as a terminal complication of carcinomatosis had no index positive, while
36% of the patients with noninfectious
December 1973
UNSTIMULATED NBT TEST
illness had no index positive. Although
the four indices are strikingly similar in
that each is positive in approximately 60%
of patients with bacterial infection and
approximately 25% of patients with noninfectious illness, it can be seen that the
NBT as a single test is not as reliable
an indicator of bacterial infection as any
of the other three taken alone.
T h e best prediction obtainable was seen
when any two of the indices were positive.
We found that if one had available only
the three more common acute-phase indices, that is, ESR, neutrophil count, and
temperature, and if the criterion for strong
suspicion of bacterial infection was that
at least two of these must be positive,
then 75% of patients with bacterial infection meet the criterion and 17% of patients
with noninfectious illness have "false-positive" results. If, however, one had four
indices available (ESR, neutrophil count,
temperature, and NBT test) and the
criterion for strong suspicion of bacterial
infection was that at least two of these
four must be positive, then 89% of patients
with bacterial infection meet the criterion
and 25% of patients with noninfectious
illness have "false-positive" results. The patients with noninfectious illness who were
positive according to this combination of
indices had ulcerative colitis, fibrinous pericarditis, disseminated intravascular coagulation secondary to ruptured ectopic pregnancy, pancreatic carcinomatosis, polymyalgia rheumatica, psoriasis, and allergic
granulomatous vasculitis.
Discussion
The main goals of this investigation
were: (1) to adapt the unstimulated NBT
test for use in a general hospital laboratory
and to compare it with the original method
of Park et al.; (2) to examine the inherent
variability of this somewhat subjective procedure by performing simultaneous duplicate assays in a manner such that the
source of the cells was unknown at the
849
time of the evaluation; (3) to extend observations of the NBT test in an adult
patient population; (4) to compare the
NBT
test with other
indices
of
inflammation.
The Park method was modified to employ readily available materials and procedures for phlebotomy, and the number
of steps involved was decreased. Our
modified procedure and the Park method
appear to be comparable in discriminating
bacterial infection when done blindly, each
method failing to correlate NBT test result with underlying diagnosis 24% of the
time when the two methods were directly
compared on the same 45 subjects.
T h e laboratory error of the Park
method, however, was substantially greater
than that of the present method, although
the disagreement between the two test
methods was greater than the laboratory
error could account for by itself. But since
neither test reflects the true clinical state
to an adequate degree, neither test can
be incriminated as the one which upsets
the between-test correlation.
The results of this study stand in sharp
contrast to the results of two earlier studies
which found the NBT test to be a very
satisfactory index of bacterial infection. 1216
However, our data are in substantial agreement with other studies. In a study of
356 pediatric patients, Feigin et al.6 found
that 11% of patients with bacterial infection had false-negative tests and 20% of
a controlled population known not to have
bacterial infection had false positive tests.
In a series of 296 pediatric patients, Humbert et al.10 noted that the test was falsely
negative in 17% of patients with bacterial
infection and positive in 4% of their controlled population. Attempts to employ
the unstimulated NBT test in specific
clinical situations, i.e., monitoring of intravenous catheter infections and infection
in renal transplant patients, have yielded
inconclusive results. Only two of 15 patients
with intravenous catheter infection had
850
BITTNER ET AL.
B. POPULATION OF
NON-INFECTIOUS
ILLNESS
A. POPULATION OF
BACTERIAL INFECTION
20
40
40
60
1st T E S T
A.J.C.P. —Vol. 60
C. POPULATION OF
NON-BACTERIAL
INFECTION
0
20
40
0. CONTROL
POPULATION
20
60
%NBT©PMN
Grophs A,B,C and 0 demonstrating within-test correlation between simultaneous duplicates (present method 152 tests in 4
clinical categories). First slide read is on abscissa, second on ordinate.
F. P O P U L A T I O N OF
NON-INFECTIOUS
ILLNESS
E. POPULATION OF
BACTERIAL
INFECTION
G. CONTROL
POPULATION
z
2
a.
©
20
40
60
0
20
1st T E S T
40
60
%NBT©PMN
Graphs E, F and G demonstrating within-test correlation of simultaneous duplicates (Park Method
4 2 tests in 3 clinical categories). First slide reod is on abscissa, second on ordinate.
I. POPULATION
H. POPULATION OF
BACTERIAL INFECTION
OF
NON-INFECTIOUS
ILLNESS
J. CONTROL
POPULATION
60
a
o
I
£
a. 4 0
UJ
©
2
l-
c
z
CM
B*
20
r = -0.42
20
40
60
0
20
1st METHOD
40
60
0
%NBT©PMN
Graphs H, I, J demonstrating between-test correlation of two test methods ( 4 2 tests in 3 clinical categories) Present method on abscissa, Park Method on ordinate. Points represent the mean
of the simultaneous duplicate N B T © P M N counts for the two methods on a given patient.
FIG. 3. Within-test and between-test correlation: present method and Park method.
December 1973
851
UNSTIMULATED NBT TEST
Table 2. NBT Test Compared with Other Inflammatory Indices:
Subgroup of 103 Subjects
Pyoge nic
Infections
Total subjects
All four positive
None positive
Erythrocyte sedimentation rate
^ 50 mm./hr.
Polymorphonuclear leukocytes
^ 9,000 c/mm. 3
Temperature S 37.7 C.
NBT -2. 8%
Any two, NBT not available
Any two, NBT available
Any one index
Noninfectious
Illnesses
Non-bacterial
Infections
Not mal
Controls
Total
%
Total
%
Total
%
Total
%
44
7
1
36
1
13
0
54
10
0
8
—
3
36
13
0
7
—
16
2
29
66
9
25
3
23
0
0
24
34
25
33
39
43
55
77
57
75
89
98
7
9
11
6
9
21
19
25
31
17
25
58
1
6
0
4
4
6
8
46
0
31
31
46
0
0
2
0
0
2
0
0
20
0
0
20
0
80
Table 3. Accumulated Misdiagnoses by N B T Test
False Negatives
False Positives
From the literature*
Streptococcal cellulitis
Chronic granulomatous disease
Myeloperoxidase deficiency
G-6-PD deficiency of neutrophils
Congenital agammaglobulinemia
Mixed cryoglobulinemia
Lipochrome histiocytosis with rheumatoid arthritis
Nephrotic syndrome with pneumococcal peritonitis and
pneumococcal bacteremia
Sickle-cell anemia with pneumococcal meningitis or
salmonella osteomyelitis
Local infection
Histiocytosis X
Shunt infection
Alcoholism with abscesses
Burn infection
Pneumonia with influenza infection
Ineffective antibiotic therapy
Corticosteroid therapy (conflicting reports)
Phenylbutazone therapy (in guinea pigs)
Osteomyelitis in diabetes mellitus
Uncomplicated urinary tract infection
Malaria
Candidosis
Aseptic meningitis
ECHO virus infection
Herpes simplex and zoster infections
Non-bacterial pneumonitis
Acute rheumatic fever
Active juvenile rheumatoid arthritis
Neonates
Congestive heart failure
Chediak-Higashi syndrome
Osteogenesis imperfecta
Hemophilia
Multiple drug overdosage
Typhoid-paratyphoid vaccine
Hodgkin's disease
Oral contraceptive use
Loaiasis
Trichinosis
Amebic hepatic abscess
Normal controls
From the present study
Endometritis
Infection in debilitated persons:
Meningitis
Pneumonia
Abdominal abscess
Carcinomatosis with septicemia
Pseudomonas endocarditis
Tertiary syphilis
UTI and septicemia in patient with syringomyelia
Ulcerative colitis
Asthmatic attack
Psoriasis
Penicillin allergy
Transfusion reaction
Polymyalgia rheumatica
Allergic granulomatous vasculitis
Rheumatoid arthritis in an adult
* False negatives, references 3, 4, 10, 12, 15, 20. False positives, references 1, 2, 5, 9, 10, 12, 14, 17, 19.
852
BITTNER ET AL.
A.J.C.P. —Vol. 60
increases in their NBT counts associated values in the NBT test which were beyond
with acute infection. 8 Five of seven renal- the range of normal without any evidence
transplant patients subsequently proved for superimposed bacterial infection. Most
to have bacterial infection and had demon- of these patients with falsely positive tests
strable rises in % NBT-positive neutro- could be loosely classified as having been
phils. 21 All seven, however, developed immunologically challenged.
marked fever. Pyrexia was a more reliable
We found the N B T test to be no more
indicator of pyogenic infection in this concordant with bacterial infection than
series. A possible explanation for the con- the other common indices of inflammation
trasting findings concerning the test's (fever, neutrophilia, Wintrobe sedimentareliability is that the laboratory technics tion rate) and, in fact, it was less reliable
employed by us (and in studies with com- than any one of the other three alone.
parable results) were defective. On the When combined with the usual indices of
other hand, all histochemical versions of bacterial infection, the N B T test increased
the test involve subjective judgment, and the frequency with which bacterial infecwhen the diagnosis or clinical status of the tion was detected by 14%, but also inpatient is known, the possibility of in- creased the frequency with which patients
advertent bias may lead to a much greater with non-bacterial infections would have
agreement with the final diagnosis than been misdiagnosed by 8%.
is inherent in the test itself. There is no
We conclude, therefore, that the NBT
indication that the more positive studies
test
may possibly be useful as an adjunct
were done blindly.
to other indices of infection, but that in
In either case, a major objective of this a severely ill adult population it does not
study was to test the hypothesis that the discriminate well between a population of
NBT test would be useful in a general patients known to have bacterial infechospital in discriminating between severely tion and a population of patients who have
ill patients with bacterial and non-bacterial other illnesses.
illness. We find no evidence to support
this hypothesis.
References
Our data confirm previous observations
1. Anderson B: NBT test in malaria. Lancet 2:
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