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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 26, No 6, November/December 2015
AFRICA
205
H-FABP is released from the myocardium into the circulation
within one to three hours of myocardial injury. Its concentration
in the blood peaks within six to eight hours and decreases within
24 to 30 hours.
10
Its properties of being abundantly available
in myocardial tissue, intra-cytosolic dominancy, relative tissue
specificity, and early elevation in blood and urine after AMI
suggest that H-FABP may be used in the early diagnosis of
ACS.
11,12
Its plasma kinetics and secretion are similar to that
of myoglobin, therefore, it is used as a marker for the early
diagnosis of ACS.
13
There are few studies on this topic and the results of previous
studies are controversial.
14-19
In our study, we aimed to evaluate
the diagnostic effectiveness of H-FABP in the early diagnosis
of NSTEMI and to compare it with other cardiac markers,
including CK-MB and troponin I (TnI) levels.
Methods
Forty-eight patients who were admitted to the emergency
department within the first 12 hours of onset of ischaemic-type
chest pain lasting for longer than 30 minutes, and who did not
have ST-segment elevation on ECG, were included in the study.
The patients who had newly developed left bundle branch block,
who were admitted more than 12 hours after the onset of chest
pain, who had chronic renal failure, chronic muscular diseases
or heart failure, or who had recently experienced trauma,
musculoskeletal injury or shock, were excluded from the study.
A detailed medical history was obtained from each patient
and a physical examination was performed. Twelve-lead ECGs
were obtained and the changes were recorded. A complete
blood count, biochemical tests and urgent cardiac profiles
(CK-MB mass, myoglobin and TnI levels) were obtained from
venous blood. Bedside H-FABP level was also determined
from the same blood sample. The patients were monitored for
24 hours, and urgent cardiac profiles and ECG monitoring
were performed every six hours. NSTEMI was diagnosed in 24
patients as the result of 24-hour follow up, and the remaining 24
patients did not develop MI.
The blood samples were immediately sent to the biochemistry
laboratory of our hospital to measure TnI and CK-MB levels.
Blood was taken in a 5-cm
3
plain tube and centrifuged at
3 000 rpm for 10 minutes. The serum was separated and loaded
into a Beckman Coulter Access II device and analysed with
chemiluminescence. Measurement of the cardiac markers in each
sample was completed within 30 to 45 minutes. The reference
values of the cardiac markers were
<
0.04 ng/ml for TnI (
<
0.04
μ
g/l) and 0.6–6.3 ng/ml for CK-MB (0.6–6.3
μ
g/l).
All patients were also tested with the CardioDetect
®
(Med-Rennessens, Niemcy, Poland) H-FABP immunotest. It
is a rapid chromatographic immunoassay method designed for
qualitative determination of H-FABP levels in blood samples.
Three to four drops of capillary blood were dropped onto a
CardioDetect kit and left on a flat surface for 15 minutes. Double
lines were interpreted as positive, a single line was negative, and
no lines was interpreted as inadequate material. H-FABP
>
7
μ
g/l
was seen as positive in this test.
20
H-FABP was tested only once
in each patient, as the number of kits was limited.
TnI and/or CK-MB elevation (verified with at least two
different measurements) associated with ischaemic-type chest
pain for over 30 minutes and without persistent ST-segment
elevation was accepted as NSTEMI, regardless of ECG change,
as recommended by the ESC/ACC committee.
6
Statistical analysis
All data were transferred to the SPSS 10.0 statistics program.
The Student’s
t
-test was used for a comparison of the groups
when parametric assumptions were realised, and the chi-square
and Fisher’s exact tests were used as a comparison and an
association of the categorical data, respectively. Screening test
results are also given. A
p
-value of
<
0.05 was considered
statistically significant.
For calculation of sample size, as a guideline we used the
results of a study conducted by Ruzgar
et al
.,
21
in which a
sensitivity of tnI and H-FABP was 0.38 and 0.95, respectively.
However, in order to be more conservative, sample size was
calculated based on a sensitivity of tnI of 0.38, sensitivity of
H-FABP of 0.8, pre-test probability of 0.6, power of 0.8, and
type 1 error rate of 0.05 (with 95% confidence). We found the
required sample size to be 43, and our study group consisted of
48 people.
For an assessment of the diagnostic performance of cardiac
markers in the diagnosis of NSTEMI, sensitivity, specificity,
negative predictive value (NPV), positive predictive value
(PPV) and the accuracy index (AI) of each marker were
calculated according to admission times. Diagnostic sensitivity
was calculated by dividing the number of patients who were
diagnosed with NSTEMI using H-FABP, CK-MB or TnI levels
by the number of patients who were diagnosed with NSTEMI,
as recommended by the ESC/ACC committee.
6
Diagnostic
specificity was calculated by dividing the number of patients
who were diagnosed without NSTEMI using H-FABP, CKMB
or TnI levels by the number of the patients who were diagnosed
without NSTEMI, as recommended by ESC/ACC committee.
6
PPV was calculated as the ratio of the number of patients
with NSTEMI with positive test results to the number of all
patients with positive test results. NPV was calculated as the ratio
of the number of patients without NSTEMI with negative test
results to the number of all patients with negative test results.
Accuracy index was the ratio of the sum of the true-positive
(positive marker and NSTEMI) and true-negative (negative
marker and no NSTEMI) patients to the number of all patients.
The accuracy shows that a cardiac marker can be used as the
criterion for an acceptable diagnostic marker for diagnosis of
MI.
NSTEMI +
NSTEMI –
Test +
a
b
Test –
c
d
Sensitivity
=
a
______
(a + c)
Specificity
=
d
______
(b + d)
PPV
=
a
______
(a + b)
NPV
=
d
______
(c + d)
Accuracy
=
(a + d)
____________
(a + b + c + d)
.