With the availability of POC A1c tests, physicians can get results and adjust treatment regimens during patient visits.
Point-of-care A1c analyzers provide immediate results, facilitating patient education and consultation, and improving patient compliance.
With a worldwide annual growth rate of approximately 15%, point-of-care (POC) testing is one of the fastest-growing segments of the IVD market. Advances in technology have resulted in fast, easy-to-use assays that offer laboratory-quality results in minutes. The number of POC tests continues to grow as IVD manufacturers develop additional assays to better serve this market. This article presents an overview of diagnostic tests for glycated hemoglobin (HbA1c or A1c), one of the major assays currently found in POC settings. The article also examines POC testing environments and methodologies, and future trends in this area.
Diabetes mellitus is a chronic disease caused either by a lack of insulin, or by insufficient production or utilization of insulin, resulting in elevated blood glucose levels. Accounting for approximately 5–10% of diabetics, type 1 diabetes develops when the insulin-producing pancreatic beta cells are destroyed by the body's immune system. No insulin is produced, and insulin injections are required to stay alive. Type 2 diabetes results when insufficient levels of insulin are produced or the body's cells become less sensitive to the hormone. Blood glucose levels may be controlled by diet, exercise, and oral medications. Diabetes-related complications include diabetic retinopathy, renal failure, diabetic neuropathy, foot ulceration, lower-limb amputation, and heart disease.
By 2025, approximately 300 million individuals worldwide will be afflicted with diabetes mellitus.1 India, China, and the United States are expected to be the most affected, with estimates of 57, 38, and 22 million diabetics, respectively. Pakistan, Indonesia, Russia, Mexico, and Brazil are also projected to have diabetic populations greater than 10 million each. In addition, the impact will be significant in developing countries where the majority of diabetics in 2025 will be 45–64 years old, typically a person's most productive working years.
Figure 1. (click to enlarge) Percentage of U.S. adults (ages 18 and over) who were diagnosed with diabetes between 1980 and 2000. The percentages are adjusted according to pre-1997 NHIS reports.
In fact, the United States may currently be experiencing a diabetes epidemic.2 Figure 1 presents the percentage of U.S. adults (ages 18 and over) who were diagnosed with diabetes between 1980 and 2000. The acceleration in the diabetic rate began in the early 1990s and has continued into the 2000s. The National Diabetes Information Clearinghouse statistics for 2005 revealed that 9.6% of Americans over the age of 20 are afflicted with the disease.
The societal and individual burdens of diabetes are significant and continue to grow as the diagnosed diabetic population increases. In 2007, the financial cost of diabetes in the United States alone was estimated at $174 billion.3 Disease-related medical expenditures accounted for $116 billion, while reduced national productivity represented $58 billion. On average, at the individual level, a diagnosed diabetic can incur annual medical expenses approximating $12,000, which is 230% higher than the costs incurred without the disease.
Two commonly tested markers for monitoring diabetes are glucose and A1c. The blood glucose test measures the level of glucose in the patient's blood at the time the sample is obtained. As such, this test provides useful, although limited, information on the diabetic's glycemic condition. POC glucose monitoring is widespread in the professional and home environments. This article will focus on the A1c test and its utilization in the POC testing environment.
Hemoglobin A1c is an indicator of long-term glycemic control that healthcare professionals use to make treatment decisions in order to maintain or improve a diabetic's glycemic level. A1c is formed by nonenzymatic glycation of the N-terminal valine of the ß-chain of hemoglobin in red blood cells. The amount of glycated hemoglobin is directly related to the average level of glucose in the blood. As blood glucose concentrations rise over time, the percent of glycated hemoglobin rises proportionally. Since circulating erythrocytes have an average half-life of 60–90 days, A1c can indicate glycemic control over a 2–3-month period. While 4–6% of the hemoglobin is glycated in nondiabetics, uncontrolled diabetics may exhibit levels in excess of 15%.
In 1993, the Diabetes Control and Complications Trial (DCCT) established that the development and progression of complications of type 1 diabetes is closely related to A1c levels.4 Similarly, the United Kingdom Prospective Diabetes Study demonstrated that lowering blood glucose levels in type 2 diabetics reduced the incidence of microvascular complications. Supported by these landmark studies, the American Diabetes Association (Alexandria, VA) recommends at least two A1c tests per year for patients who are meeting treatment goals, and quarterly tests for patients whose therapy has changed or individuals who are not meeting glycemic goals.5 In addition, the ADA recommends the use of POC testing for A1c to allow for timely decisions on therapy changes.
Table I. (click to enlarge) Analysis of Medicare claims for the top 10 tests performed in U.S. physician office laboratories.
An analysis of Medicare claims shows the significance and magnitude of POC A1c testing (see Table I).6 In 2003, A1c assays represented 2.3% of total physician office laboratory (POL) testing. Only complete blood count, prothrombin time, comprehensive metabolic panel, lipid panel, basic metabolic panel, and thyroid-stimulating hormone were more commonly tested in POL settings. In addition to accounting for 2.3% of total POL testing, A1c experienced double-digit growth from 2001 to 2003.
A1c Test Availability
The majority of A1c tests are performed in hospital and reference laboratories, using either high-performance liquid chromatography (HPLC), which is often considered the gold standard, or immunoassay methods. However, with off-site testing and long turnaround times, A1c test results are provided to physicians after the patient visits, and are not available when treatment decisions are considered.
POC A1c Testing
A lack of immediate A1c test results can affect the clinical decision-making process and lead to delays in adjusting treatment regimens. Failure to adjust treatments properly may lead to decreased patient compliance and an increased risk of complications from the disease. With a desire to improve patient care, physicians are embracing POC A1c testing to ensure the availability of A1c results during the patient visit. Advances in technology have enabled IVD manufacturers to develop POC A1c testing platforms that provide the following benefits to physicians and patients.
Improved Patient Care. The rapid processing time of POC A1c assays generates A1c results in minutes and provides test results during patient visits. Evidence supports that POC A1c testing improves glycemic control in not only the short term (less than 1.5 years) but also the long term (3.5 years), potentially delaying the onset and magnitude of complications from the disease.7 In addition to improving glycemic control, studies have shown that POC A1c helps improve communication and collaborative efforts between physicians and patients in managing the disease.8
Standardized Results. All POC A1c assays in the United States are certified annually by the National Glycohemoglobin Standardization Program (NGSP). The purpose of NGSP certification is to standardize glycated hemoglobin test results so that they are comparable to results reported by DCCT. Certification requires analyzing 40 samples and having an assessment of agreement analysis of 95% confidence interval of differences within ±0.85% glycohemoglobin. POC A1c analyzers are required to comply with the same rigorous standards that laboratory HPLC systems must meet. This certification assures that POC A1c test results are anchored to a reference standard and will be similar to results from hospital laboratories.
Laboratory-Quality Results. Having accurate A1c test results is crucial to effectively treating diabetics. Physicians must be confident that the results accurately reflect the patient's glycemic status. Data from the 2007 GH2-B survey by the College of American Pathologists (CAP; Northfield, IL) demonstrated the laboratory-level accuracy and precision of most POC A1c assays. The survey also demonstrated strong POC A1c test result agreement with laboratory-based HPLC and immunoassay systems.
For the three survey samples (6.2%, 9.2%, and 11.1% A1c), automated POC analyzer means differed by 0.1%, 0.4%, and 0.1% A1c, respectively, from the known reference value. In the clinically significant range of 6–9% A1c, automated POC A1c analyzers were precise and reproducible with coefficients of variation (CV) of 2.9–3.0% for reference samples of 6.2% and 9.2% A1c. Such precision levels were better than many laboratory-based immunoassay systems with reported CVs of 3.6–5.7%.
Compact Size. POC A1c analyzers are smaller than HPLC or immunoassay analyzers used in laboratories. The small footprint allows the POC A1c analyzers to be used in environments where testing space is limited. Portability also allows multiple site testing or the option of professional in-home or field testing.
Easy-to-Use Assays. POC testing environments span a large range of testing locations: physician offices, pharmacies, clinics, small hospitals, health fairs, and other nonclinical settings. Operator skills and training will vary greatly in these market segments. POC A1c assays overcome this obstacle with analyzers providing full automation, self-calibration, and firmware that identifies and reduces potential operator errors. In the United States, most POC A1c assays are CLIA-waived, enabling existing physician office staff to perform the tests.
Patient Comfort. A common complaint from physicians and diabetes educators is that patients often fail to report to the lab for their A1c test. The inconvenience of traveling to another location and the discomfort of providing a venous sample have been noted as the primary reasons. POC A1c testing overcomes these obstacles. Fingerstick samples eliminate the emotional fears of providing venous samples and are collected with less discomfort to the patient.
Revenue Potential. Private insurance and Medicare reimbursement for in-office POC testing can provide increased revenues and profits for POLs. As reported in an analysis by the Medicare Payment Advisory Commission (MedPAC; Washington, DC) in 2006, A1c assays represented 3.3% of total Medicare payments for POL testing. With a projected average annual growth rate of 13%, A1c testing will remain an important marker on the POL testing menu.
As with centralized laboratory systems, POC A1c testing platforms utilize various technologies. Current assays use boronate affinity chromatography, immunoassays, or micro-optical detection methods (MODM). Since HPLC, cation exchange chromatography, and many other immunoassay methods are typically cleared by FDA as moderately complex devices that require skilled technicians to operate, they are seldom used in POC testing.
Boronate Affinity Chromatography
Affinity chromatography utilizes boronic acid to separate glycated and nonglycated hemoglobin. Studies from 1981 support this methodology for the quantization of glycated hemoglobins.9 Sample reagent lyses the red blood cells, and after mixing and incubation, the glycated hemoglobin binds to the boronate affinity resin. After separation, the nonglycated hemoglobin is photometrically measured. After a brief wash step, elution buffer using sorbitol elutes the glycated hemoglobin off the boronate affinity resin. The glycated hemoglobin is released from the boronic acid sites on the resin as sorbitol more effectively competes with the gylcated hemoglobin for these sites. The concentration of glycated hemoglobin is measured, and the %A1c is calculated from the absorbance measurements using a simple algorithm.
Affinity chromatography is not significantly affected by most hemoglobin variants, fetal hemoglobin, or labile Schiff base.10
Figure 2. The in2it analyzer by Bio-Rad Laboratories Inc. (Hercules, CA).
An example of a fully automated boronate affinity assay is the in2it POC analyzer by Bio-Rad Laboratories Inc. (Hercules, CA) (see Figure 2).
Immunoassay tests measure the concentrations of A1c and total hemoglobin, and report the ratio as a percentage of hemoglobin A1c. Specific A1c is measured by using inhibition of latex agglutination. Assay reagents contain latex particles coated with A1c-specific antibodies and an agglutinator with numerous copies of the immunoreactive portion of A1c. The A1c in the patient sample competes for antibody binding sites on the latex particles, resulting in an inhibition of agglutination. The agglutination process causes increased light scatter and a corresponding increase in absorbance when the measurement is taken. As agglutination is inhibited, the scattering of light is decreased, resulting in decreased absorbance. A calibration curve of absorbance and corresponding A1c concentration quantifies the A1c percentage from the absorbance readings.
The DCA2000 by Siemens Healthcare Diagnostics (Deerfield, IL) is an example of a POC A1c analyzer utilizing immunoassays. Launched in 1992, the DCA2000 was the first clinic-based analyzer for measuring A1c. The automated procedure delivers results using venous or capillary samples. Studies have indicated potential interference from hemoglobin F and C. Artificially low A1c results may be reported in the presence of high levels of HbF, and a significant positive bias in patients with an HbC trait has been observed.11,12
Micro-Optical Detection Methods
The MODM technology incorporates immunoassays and chemistry technology to report A1c test results by using a handheld monitor and single-use test cartridges. The assay measures both A1c and total hemoglobin. Developed by Metrika Inc. (Tarrytown, NY), the semimanual procedure is used in the A1cNow+ device and includes various pipetting, mixing, and timing steps.
According to CAP's 2007 GH2-B survey, the Metrika A1cNow+ test was the only assay reporting between-laboratory CVs greater than 5% on all three samples. The assay also showed a significantly large negative bias on two of the three samples. Biases of –1% A1c and –0.9% A1c were reported for these samples with reference values of 9.2% and 11.1%, respectively.
However, the assay has several limitations noted in the product insert that potentially affect test result accuracy. One primary concern is HbS interference due to the frequency of this hemoglobin variant in African-Americans.
Studies have cautioned against using this assay methodology for children with type 1 diabetes because a large percentage of patient results differed from reference values by more than 0.5% A1c.13 Previous studies have also demonstrated similar inaccuracies against laboratory reference methods. A1cNow+ test results from 6231 patients reported that 32% differed from an HPLC reference method by more than 0.75%, and 20% varied by more than 1.0%.14
Trends in POC A1c Testing
POC A1c testing has emerged as a major factor in diagnostics testing. Fast, accurate results are now available for many analytes, enhancing physicians' abilities to treat their patients effectively. Further growth in POC A1c testing will be fueled by the rapidly rising diagnosed diabetic population. Other future market drivers will enhance test availability, provide assurances of result quality, and enable electronic connectivity.
Multianalyte Menus. Test menus may include disease states (e.g., A1c), glucose, and microalbumin for diabetes monitoring, or they may be broad based to cover commonly tested analytes. Such expanded menus will provide work flow efficiencies as operator training requirements are minimized.
Shift to CLIA-Waived Tests. The increased difficulty in performing nonwaived tests on patients is causing POLs to shift to CLIA-waived tests. In 2003, CLIA regulations required validation of assays prior to using the methods for testing patients. Such validation involves additional time and expense to train operators in validation and procedural guideline development.
There are also financial incentives to move away from nonwaived tests. Unlike nonwaived laboratories, CLIA-waived laboratories are not subject to inspections or proficiency testing. While a CLIA certificate costs $150 every two years, nonwaived facilities may incur volume-related fees of up to several thousand dollars for the same time period. Currently, the in2it analyzer, the Micromat II by Bio-Rad Laboratories, the Bayer Metrika A1cNow+, the Siemens DCA2000, and the Afinion by Axis-Shield plc (Dundee, Scotland) are CLIA waived.
Quality Control Assurance. Centralized POC testing coordinators will strive to ensure that results are generated by trained operators using analyzers and reagents that are performing correctly. In addition, sample traceability will ensure that test results are properly assigned to the correct patients. The firmware will need the ability to enforce compliance in such areas, and the hardware must allow entry of patient and operator identification information.
Barry Plant is senior product manager, clinical systems division, at Bio-Rad Laboratories Inc. (Hercules, CA). He can be reached at barry_plant@
Electronic Connectivity. With the emergence of electronic medical records, POC analyzers will need to provide seamless connection to patient records. Such connectivity will ensure that potential transcription errors are eliminated and patient records are automatically updated.
Although well established, POC testing in general and POC A1c testing in particular are still young markets that will continue to mature over time. MedPAC estimates that POLs currently account for 17% of existing laboratory testing. This percentage will grow as IVD companies develop tests and analyzers that address the future trends and needs of the POL market. As this market matures and test offerings expand, POLs will compete with centralized laboratories for testing volumes.
POC A1c testing is rapidly becoming a key tool for physicians to monitor and effectively treat their diabetic patients. Same-visit test results provide vital information in making treatment decisions during the patient's visit. This benefit will continue to drive POC A1c testing expansion.
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8. J Brown et al., “Point-of-Care Testing in Diabetes Management: What Role Does It Play?” Diabetes Spectrum 17 (November 4, 2004).
9. AK Mallia et al., “Preparation and Use of a Boronic Acid Affinity Support for Separation and Quantitation of Glycosylated Hemoglobins,” Analytical Letters 14 (1981): 649–61.
10. WG John, “Glycated Haemoglobin Analysis,” Annals of Clinical Biochemistry 34 (1997): 17–31.
11. D Sabath, “Case Study: Artifiactually Low Hemoglobin A1c in a Patient with High Hemoglobin F,” Clinical Diabetes 18, no. 4 (Fall 2000).
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13. L Fox et al., “The DirecNet Study Group: Relative Inaccuracy of the A1cNow in Children with Type 1 Diabetes,” Diabetes Care 30, no. 1 (January 2007).
14. L Kennedy and WH Herman, “Glycated Hemoglobin Assessment in Clinical Practice: Comparison of the A1cNow Point-of-Care Device with Central Laboratory Testing (Goal A1c Study),” Diabetes Technology & Therapeutics 7 (2005): 907–912.