Acute-care testing at the point of care: now and in the future

Aug. 1, 2009

The field of point-of-care testing (POCT) is entering
a period of rapid expansion. This expansion is being driven by new
evidence for clinical effectiveness of POCT and new technologies that
allow consolidation of testing onto smaller platforms. Technological
improvements will also lead to increased accuracy for point-of-care
tests, which will facilitate the transition of more central-lab testing
to the bedside.

Adoption of POCT as a patient-care solution has been
hampered by concerns over cost of testing, analytical accuracy of POCT
solutions, data management, and evidence for improved patient-care
outcomes when POCT is employed. While cost and data management will not
be covered in this review, there has been significant progress on both
fronts. The focus of this article is on advances in defining the
evidence for improved outcome with POCT, and advances in analytical
accuracy driven by platform consolidation and new technologies.

NACB practice guidelines

In 2007, the National Academy of Clinical
Biochemistry (NACB) released the final version of the practice guideline
“Evidence-based Practice for Point-of-Care Testing.”1 The
document is broken down into 13 chapters, with each chapter reviewing
evidence for the use of point of care in a given clinical area or for a
given set of analytes (i.e., critical-care testing, infectious-disease
testing, coagulation). The strength of evidence for improved patient
outcome was graded from A to C.

A grade of “A” indicates that point-of-care (POC) experts
reviewed the available evidence and concluded that the use of POC testing
improves important health outcomes. Thus, “A” is the strongest
recommendation given by the committee. A grade of “B” indicates that use
should outweigh harm, or that there was at least fair evidence that
important health outcomes could be improved through the use of POCT. A grade
of “C” indicates that harm outweighs use; that is a recommendation against
the adoption of POCT. A grade of “I” indicates that there is currently
insufficient evidence to make a recommendation.

The chapter on critical care (Chapter 5) may be of most
interest. The chapter evaluates evidence for POCT for arterial blood-gas
(ABG) analysis, glucose, lactate, magnesium, CO-oximetry, electrolytes, and
ionized calcium. The clinical benefits of POCT ABG were evaluated in three
different settings: the intensive care unit (ICU), emergency department
(ED), and cardiac surgery.

The authors found fair evidence (grade of “B”) for POCT
ABG when used in the ICU. The most compelling data on patient outcome with
ABG testing in the ICU occurred in the setting of goal-directed therapy for
the early detection and treatment of sepsis and shock.1 POCT ABG
was effective in a randomized trial of patients presenting to an urban ED
and admitted to the ICU with either sepsis or shock. The study found that
using POC methods to monitor blood gas and lactate reduced mortality
compared to patients receiving conventional treatment.2

Regarding POC relative to laboratory blood-gas testing,
the guidelines state that in some facilities POC blood-gas analysis may
offer little time savings compared to central-lab analysis of ABG. In
addition, there was no consensus reached on the cost-effectiveness of POC
ABG testing (grade of “I”).1 The cost-effectiveness of POC
blood-gas testing is likely dependent upon the existing laboratory structure
and turnaround time (TAT) within the facility. Specifically, a significant
reduction in TAT3 and elimination of laboratory staff4
may be necessary to show the cost effectiveness of POC blood-gas analysis.
In facilities with STAT laboratories dedicated only to blood-gas analysis,
elimination of STAT laboratories in favor of POCT approaches may be cost
effective.4 If ABG samples are currently analyzed in STAT or
central labs that offer rapid TAT and perform many different tests (some not
available on POCT platforms), then cost effectiveness may be more difficult
to demonstrate.

The guidelines conclude that evidence was only fair
(grade of “B”) for use of POC ABG in other patient-care areas such as the ED
and cardiac surgery. In the ED, the best evidence for improved patient
outcomes with POC blood-gas use was related to the early recognition of
shock or metabolic acidosis using pCO2 at the bedside. Some
institutions, however, have found that lactate — discussed here under
“Lactate measurements” — may be as or more valuable for this purpose.

Glucose measurements

Glucose testing by POC received a grade of “A” because
the use of POCT has been associated with improved patient outcomes. For
glucose, it was noted that the implementation of tight glycemic-control
protocols that rely on POC glucose testing improves outcome for critically
ill patients. POC glucose testing also allows the rapid detection of
hypoglycemia in patients on insulin therapy and, thus, can reduce harm.
Glucose testing by POC was strongly endorsed by the guideline’s authors
because there was a demonstrated reduction in TAT for results; and, in
addition, there was evidence that the reduced TAT led to improved patient

Although glucose measurement at the point of care was
strongly endorsed by the NACB guidance document, glucose POCT for critically
ill patients is not without controversy. Two recent editorials raised
questions about whether the current generation of hand-held glucose meters
is accurate enough for use in managing critically ill patients on tight
glycemic-control protocols.5,6 Studies examining the accuracy of
POCT glucose measurement in this population have found that the use of
blood-gas analyzers results in improved accuracy compared to hand-held
glucose meters,7,8 but the use of larger devices, such as
critical-care or blood-gas analyzers, may not be feasible in all

Newer glucose-meter devices with improved accuracy have
recently become available that may close the gap between the analytic
performance of blood-gas analyzers and hand-held glucose meters.9
The appropriate manner in which to monitor glucose concentrations for
critically ill patients and the degree of accuracy required for this patient
population will continue to be debated and studied in the coming years. In
the meantime, institutions must weigh convenience, workflow, cost, and
quality considerations carefully when considering a POCT solution for
glucose monitoring of critically ill patients.

Lactate measurements

Lactate was the other critical-care analyte to receive an
“A” recommendation based upon evidence of improved TAT and improved patient
outcome. The most compelling data supporting the use of point-of-care
lactate again comes out of studies examining the rapid detection and
treatment of sepsis and shock.1 Recognition and treatment of
sepsis has become both a priority and a quality indicator for some
healthcare systems.

One recent study found that patient outcomes were
improved when POC lactate measurement was used to support goal-directed
therapy to keep lactate levels below set thresholds, compared to historical
controls that did not use POC lactate or goal-directed therapy.10
Because many laboratories struggle with rapid TAT for lactate measurement
and because more institutions are focusing on sepsis outcomes, demand for
POC lactate measurement is likely to increase.

In contrast to glucose measurement, analysis of lactate
at the point of care is less problematic. One recent study compared two
central-laboratory (plasma-based) lactate assays to three whole-blood
lactate assays. Most whole-blood lactate assays agree well with the
laboratory reference method up to ~6 mmol/L, and this allowed the correct
clinical classification of almost all patients with most devices.11
The methods studied included both blood-gas analyzers and hand-held devices;
thus, there does not appear to be an analytic limitation to the use of
lactate at the point of care for clinical decision making.

Creatinine measurements

Although the NACB guidelines found that evidence for
improved outcomes in critical-care settings was not good for POC creatinine
testing (grade of “C”), the authors of this section also note that evidence
is fair (grade of “B”) for the use of POC creatinine tests in settings
(mostly procedural areas) where rapid therapeutic decisions about dosing of
contrast agents or other drugs must be made. Many medical centers are now
focusing on preventing contrast-induced nephropathy (CIN), temporary or
permanent kidney damage caused by contrast agents in patients at risk of
renal damage. For this reason, rapid TAT for creatinine measurement may be
desired in hospital procedural areas.

Accuracy of creatinine assays used at the point of care,
however, is another area where more data is needed. Most radiology
guidelines recommend screening patients for CIN risk using the estimated
glomerular filtration rate (eGFR). Because small changes in creatinine can
result in significant changes to eGFR, some laboratory experts have
cautioned that bias and interference in current laboratory creatinine test
methods may limit the ability to accurately report eGFR.12 The
problem is further compounded with point-of-care creatinine measurement,
which is subject to even greater amounts of bias than central-laboratory
measurement.13 Close examination of the accuracy and precision of
POC creatinine testing methods, along with studies examining the efficacy of
screening for CIN risk using point-of-care creatinine/eGFR, are needed in
order to understand the utility of POC creatinine tests for risk evaluation
of CIN. One such study comparing multiple whole-blood creatinine devices for
CIN-risk prediction has recently been completed but has not yet been
published. This study found significant differences between different
whole-blood creatinine devices used for CIN-risk prediction.14
Similar to glucose and lactate, the combination of improved analytic
accuracy and evidence for improved outcome will drive the transition from
central laboratory to POC creatinine.

Consolidation of testing platforms

Consolidation of testing platforms, driven by increasing
evidence for improved patient-care outcomes for analytes, such as glucose,
lactate, and creatinine, and the desire to use a single platform in multiple
patient-care settings, is another important trend in POCT. In general,
platform consolidation has occurred in one of two ways: the conversion of
central-laboratory blood-gas analyzers into POC critical-care devices
through the use of disposable multitest, multiassay cartridges, and, in
contrast, the addition of more tests to hand-held devices that rely on
single-use cartridges.

Multiple vendors have introduced devices that can perform
tests such as ABG, CO-oximetry, and critical-care analytes on a single
platform. These devices generally perform multiple tests on a multiuse
disposable cartridge, which must be changed every few days or weeks. As a
class of devices, these offer blood gas with CO-oximetry, and along with CO-oximetry
an optically measured hemoglobin. Depending on the particular device,
glucose, lactate, and/or creatinine may also be available. Some also offer a
total bilirubin measurement for neonatal testing. These devices may also
offer onboard quality control (QC) and various forms of automated function
checks and QC tracking to simplify regulatory compliance and, potentially,
improve the testing quality. The disadvantage of these devices is that they
are not as portable as hand-held single-use devices, and operation may be
more complicated compared to hand-held devices.

The other trend has been the addition of more analytes to
hand-held devices that rely on a single-use cartridge, meaning that each
cartridge, reagent, or strip is used one time and discarded. Some of these
offer basic blood-gas analysis with a subset of critical-care analytes —
most often creatinine and lactate — or less commonly offer CO-oximetry using
a hand-held device. Those devices that do not perform CO-oximetry (most in
this class) rely on a conductivity-based hematocrit measurement rather than
an optical hemoglobin measurement for the measurement of the hemoglobin
content of whole blood.

This distinction is important mainly for one patient
population: patients on cardiopulmonary-bypass procedures. In patients with
low hematocrit who have received prime fluids used for cardiac-bypass
circuits, conductivity-based measurement of hematocrit may produce
clinically unacceptable results. This was observed in one recent study15
and is likely a limitation of most technologies that use conductivity to
measure hematocrit. The use of an optically measured hemoglobin (CO-oximetry)
may be a better option for measuring hemoglobin content during bypass.

In the near future, POCT for critically ill patients will
likely continue to evolve around consolidation of testing platforms,
concentrating on analytes that have been shown to improve outcome in
critically ill patients. Technical advances will allow more accurate
measurement of analytes that have traditionally challenged POCT platforms,
such as glucose, hemoglobin/hematocrit, cardiac markers, and creatinine.

Brad S. Karon, MD, PhD, is assistant professor of
laboratory medicine and pathology, and director of the Hospital Clinical
Laboratories, POCT, and phlebotomy services at Mayo Clinic in Rochester, MN.


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