CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 10, November 2012
532
AFRICA
The 20% limit of defining a significant increase from the
time of first assessment if baseline values are above the URL
has been established within the National Academy of Clinical
Biochemistry laboratory medicine practice guidelines
30
and
represents a significant (
>
3)
standard deviation variation on the
basis of a 5–7% analytical imprecision (analytical CV).
12,31,32
This
increment of increase has been proven to be clinically useful
8,32-35
but is assay dependent,
16,17,36-38
and remains a challenge that
requires further clinical and prospective studies, as concluded by
Lippi
et al.
and others.
9,40
The 50% limit of defining a significant
increase if baseline values are below the URL does not appear
to be based on high-level evidence but purportedly optimises the
overall accuracy of MI diagnosis.
9,11,27
Other complexities of measurement, as eluded to byThygesen,
9
are the substantial differences between ‘high-sensitivity’ assays
and the concern that the manufacturers’ claims for assay
precision cannot be achieved in clinical laboratories. Relevant
analytical issues alluded to in the SA guidelines are falsely
high values because of heterophile antibodies and human auto-
antibodies interfering with the assay,
40-42
and falsely low levels
with haemolysis.
43,44
In addition, Lippi
et al
.
4
reported interferences being observed,
caused by rheumatoid factor, complement, presence of fibrin in
serum or plasma after centrifugation of the sample, unsuitable
samples (e.g. haemolysed, lipaemic, icteric), and analytical
errors (e.g. instrument malfunctioning). Of interest is a report
by Gould
et al
.
on carry-over to subsequent samples with certain
analysers, potentially leading to false-positive results.
45
Conclusion
The South African guidelines on the use of high-sensitivity
cardiac troponins as biomarkers are timely and of great value,
provided that clinicians take up the challenge of applying them
clinically.
RHENA DELPORT, PhD (Chem Path), MSc, MEd,
Department of Chemical Pathology, School of Medicine,
Faculty of Health Sciences, University of Pretoria, Pretoria,
South Africa
JAMES A KER, MB ChB, MMed (Int), MD,
Department of Internal Medicine, School of Medicine, Faculty
of Health Sciences, University of Pretoria, Pretoria, South
Africa
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