Prolonged hypoglycemia in newborn infants is
associated with adverse neurodevelopmental consequences. Therefore, in
1996, the American Academy of Pediatrics recommended routine screening
in newborn units which take care of infants at risk for hypoglycemia
[1]. The optimum method for measuring blood glucose is laboratory
estimation of plasma glucose. Laboratory analyzers use a number of
different enzymes to measure glucose eg, glucose oxidase, hexokinase or
glucose dehydrogenase. These measure plasma glucose and are less
affected by interference by metabolites, are not affected by hematocrit
and are considered the gold standard for clinical measurement of glucose
levels. The major issues with laboratory based testing are need of a
larger volume of blood, non availability of results quickly enough for
timely appropriate treatment and errors associated with delayed
estimation [2].
Therefore ‘point of care’ (POC) testing is often used
for measurement of whole blood glucose concentration in neonatal
intensive care units. Point of care testing is defined as any analytic
testing done outside a designated laboratory space. It has several
advantages like rapid turnaround time, reduced blood volume
requirements, and clinical utility over traditional laboratory-based
testing and is especially well suited for acute care settings such as
the neonatal intensive care unit. Accuracy studies have shown that their
results correlate well with laboratory measured plasma glucose in the
normoglycemic and hyperglycemic range, but are not satisfactory in the
lower range. This is understandable as the currently used glucometers
were initially developed for glucose monitoring in adult patients with
diabetes. However, our main concern in newborn babies is the low blood
glucose range [3].
As there are accuracy issues with the simple
convenient bedside POCT devices, many workers have tried to compare
these with the gold standard laboratory estimation. When analyzing the
performance of glucometers in the hypoglycemic range, glucometers are
required to perform to the standards of the US National Committee for
Clinical Laboratory Standards (NCCLS) or the American Diabetic
Association (ADA). In 1994, the ADA recommended that a glucometer should
achieve a total error (system + user) of less than 10% for the plasma
glucose concentration range 1.6–22.2 mmol/L (30–400 mg/dL). NCCLS in
1994 ascertained that for glucose concentrations less than 5.5 mmol/L
(100 mg/dL), discrepancies should be no more than 0.83 mmol/L (15 mg/dL)
[4].
In recent years, numerous studies have been published
analyzing the accuracy of glucometers specifically in the setting of
neonatal hypoglycemia. Ho, et al. [5] reported on the sensitivity
and negative predictive value of 5 glucometers in detecting neonatal
hypoglycemia. They found that not even 1 of the 5 was able to meet the
ADA standards, whereas 2 of the devices were able to meet the NCCLS
standards. Khan, et al. [6] compared 7 glucometers and reported
agreement between glucometer readings in the hypoglycemic range but
found wide discrepancy in the correlation between reference and POCT
devices both in the hypo and hyperglycemic range to the tune of 60%. The
study by Ngerncham, et al. [7] appearing in this volume of the
journal too has used an elegant split sample design and meticulously
compared OneTouch SureStep Hospital Test Strips (photometric glucose
oxidase system) with a Nova StatStrip (modified glucose oxidase based
amperometric system) using Roche Modular P 800 for the reference
laboratory measurement. Another recent study reported good correlation
as well as recommended their use in neonatal clinical practice [8]. All
these studies highlight that POC devices may be used as screening
devices for neonatal hypoglycemia, but confirmation of hypoglycemia with
laboratory measurement of plasma glucose is still crucial.
It needs to be realized that laboratory estimation
too is fraught with preanalytical (sample collection, transport and
physiological factors) errors. POCT devices are prone for both
pre-analytical and analytical errors (precision of the device being
used). The comparison of POCT devices with laboratory sample which has
been poorly processed can lead to erroneous estimation of discrepancy
where little or none may exist. Any further studies on comparison of
POCT devices with reference standard should focus on comparing improved
second generation POCT devices with a reference laboratory device taking
utmost care to ensure precise laboratory estimation without any
processing delays and fall in glucose secondary to glycolysis.
Competing interests: None stated. Funding:
None.
References
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