Keep it Under Control

To improve the health of those with, or at risk for, diabetes, and to reduce costs for patients and health care providers, it is imperative to use an accurate, efficient, and reliable diagnostic that provides stellar glycemic control.

CONTROL OF BLOOD GLUCOSE

From 1983 to 1993, the National Institute of Diabetes and Digestive and Kidney Disease conducted the Diabetes Control and Complications Trial (DCCT) across North America and Canada. This major clinical study included more than 1,400 participants with diabetes and showed that aggressively regulating blood glucose levels slows the onset and progression of diabetic retinopathy, nephropathy, and neuropathy more than the standard method of care.¹ DCCT researchers defined intensive control as keeping glycated hemoglobin (HbA1c) levels at 7% or less.¹

HBA1C

HbA1c levels represent a person’s average blood glucose concentration history. In the 120-day life cycle of a normal red blood cell (RBC), glucose will bind with hemoglobin to form HbA1c. Therefore, HbA1c levels serve as a marker for average blood glucose concentration for a period of time (2 to 3 months) immediately prior to the measurement. In people with diabetes, the level of HbA1c is much higher than in people without the disease. The DCCT named HbA1c measurement as the gold-standard index of glycemic control for diabetics in a clinical setting.^2,3

More than 20 years after the DCCT, the market now contains a large number of assays and methods to measure HbA1c. When choosing an HbA1c assay for your clinic or laboratory, you must first consider your patient population and understand the assay’s strengths and weaknesses in relation to your population. For example, HbA1c may not be the ideal assay if a number of your patients have abnormal hemoglobin or RBC life spans (such as B12, folate deficiency, or sickle cell disease).

The National Glycohemoglobin Standardization Program’s (NGSP) Web site (www.ngsp.org) can be a valuable resource for choosing the right HbA1c diagnostic. The site lists all certified tests for HbA1c and identifies which tests do not work for variants in hemoglobin.

HBA1C ASSAYS

If a patient does not have RBC or hemoglobin anomalies (such as gestational diabetes and diabetes while on dialysis), HbA1c monitoring is more accurate and potentially a more cost-effective way to measure diabetes risk versus traditional blood glucose measurements, such as urine dip sticks. HbA1c can be monitored using a number of techniques: high-performance liquid chromatography (HPLC), immunoassay, enzymatic assay, and point of care (POC) immunoassay devices. Calibration standards and linearity controls are available for these products to assure accurate results. Several HbA1c monitoring formats and accessories will be described in this article.

DIAZYME DIRECT ENZYMATIC HBA1C ASSAY

The NSGP-certified Direct Enzymatic HbA1c Assay from Diazyme Laboratories, Poway, Calif, has no interference from hemoglobin variants including HbC, HbS, HbE, and caramylated acetylated Hb or labile HbA1c. This unique freedom from interference combined with precision provides for performance advantages over conventional assays. Diazyme’s patented enzymatic method measures HbA1c using only a single instrument channel and completely eliminates the latex particles cuvette contamination often seen in HbA1c immunoassay methods. This reduces instrument maintenance. The assay correlates well with conventional testing methods such as the Tosoh HPLC method described below.

The enzymatic assay uses lysed whole blood samples that are subjected to extensive digestion with proteases. No separate measurement for total hemoglobin is needed. The HbA1c concentration is expressed directly as %HbA1c by use of a suitable calibration curve. This enzymatic assay is intended for use in the quantitative determination of stable HbA1c in human whole blood samples and is intended for in vitro diagnostics use only.

SIEMENS DCA VANTAGE ANALYZER

The DCA Vantage analyzer from Siemens Healthcare Diagnostics, Deerfield, Ill, is primarily used by health care professionals managing patients with diabetes in a physician’s office, freestanding diabetes clinic, hospital clinic, or endocrinology department. The DCA Vantage analyzer is an easy-to-use POC analyzer that delivers HbA1c test results for managing patients’ glycemic control at the time of visit, as well as urinary microalbumin creatinine to test for early detection of nephropathy—one of the major complications of diabetes. The benefit of using a POC analyzer is that results are delivered at the time of visit, where the health care professionals can immediately make necessary adjustments to the patient’s treatment regimen.

The technology in the DCA analyzer provides laboratory-like precision and accuracy. It is one of only two POC HbA1c analyzers that passed the NGSP criteria in 2010 and is also mentioned in more than 100 clinical articles.⁴ “With multiple published studies, the DCA technology has proven that HbA1c testing at the point of care can have a positive impact on improving glycemic control. This is extremely important in a disease where even a 1% drop in HbA1c can minimize the risks of diabetes complications,” says David Stein, PhD, CEO, Point of Care Business Unit, Siemens Healthcare Diagnostics.

It is also a potential source of cost savings for the office. “The DCA HbA1c test eliminates the need for a phlebotomist to draw a sample; eliminates the transportation costs associated with sending samples to a laboratory, eliminates cost associated with patients not being compliant by not getting blood test draws prior to the doctor visit, and minimizes costs associated with nurses or physicians calling the patient with a result weeks after sample draw to discuss results,” Stein says.

TOSOH HLC-723G8 ANALYZER

The HLC-723G8 (G8) is an automated, HPLC system designed to measure HbA1c accurately and rapidly. The DCCT used a HPLC system to measure HbA1c. Therefore, it is considered the gold-standard method of measuring the protein.

To achieve the ever-narrowing accuracy and precision requirements for measuring HbA1c, analyzers should have low CVs and little to no bias. The G8 analyzer from Tosoh Bioscience, South San Francisco, Calif, leads the industry in precision with CVs of less than 2%, and is used by physicians to monitor the long-term efficacy of glycemic control. A high-quality HbA1c result is essential because it ultimately decides the course of treatment for a diabetic patient.

The variability of the HbA1c on different instrumentation is monitored through the results of the College of American Pathologists (CAP) Glycohemoglobin (GH2) proficiency surveys that are performed twice per year. “When laboratories participate in CAP surveys, they are comparing the results obtained on their system to a target value,” says Ranka Milojkovic, HPLC product manager, Tosoh Bioscience Inc. “Since grading criteria is dropping each year, it will be more difficult for laboratories to pass their CAP survey if they are using an analyzer that gives them results outside of the acceptable grading limit. Tosoh is already ahead of the accuracy grading curve, as demonstrated by current and future pass rates.”

To help improve the quality of the HbA1c testing, the CAP will further tighten its proficiency grading criteria to ±6% in 2012. The NGSP has also tightened manufacturer certification criteria to ±8%. With an instrument that provides a high level of precision, such as the G8 analyzer, users know that their results are reproducible and fluctuations are readily apparent. Also, with the G8, the ease of use allows for more time focused on patient care and less time doing equipment maintenance. These are a few examples of how the Tosoh G8 lowers the indirect costs of diabetes.

BLOCK SCIENTIFIC HBA1C LINEARITY CONTROLS

Block Scientific, Bohemia, NY, offers Phoenix Diagnostics’ HbA1c Linearity Controls. The test kit can be used as part of clinic or laboratory inspection to determine linearity, calibration verification, and verification of linear range among automated, semiautomated, and manual chemistry systems used to measure HbA1c. Unlike lyophilized alternatives, the Phoenix Diagnostic controls are ready to use and do not need reconstitution.

The linearity control line also includes a multianalyte allowing the user to test up to eight analytes (HbA1c, albumin, cholesterol, triglycerides, calcium, chloride, creatine, lactate) with one linearity control. “This allows the user to consolidate more analytes in fewer products, which offers laboratories savings of up to 30% annually,” says Danielle Nicholas, sales manager for Block Scientific.

The company’s biggest consumer for the HbA1c linearity controls includes physicians/offices/laboratories (POL) that serve populations at higher risk for diabetes, such as Hispanics and African Americans.⁵ “The HbA1c test kits stand out for two reasons: accuracy and speed,” Nicholas says. “With other kits, the user has to send the test results out to be read. This can take up to 7 days. With Phoenix Diagnostics’ linearity controls, users can access an online database that connects with the POL server and can download linearity results in less than an hour. This function is particularly useful to doctors because it gives them the ability to do linearity testing themselves without substantial time or cost.”

QUANTIMETRIX DROPPER A1C DIABETES CONTROL

The Dropper A1c Diabetes Control from Quantimetrix, Redondo Beach, Calif, offers a number of enhanced performance features, including 3 years frozen closed-vial, 6 months refrigerated, and 21 days of room temperature open-vial stability in a dropper-style format. The control is made with a whole human blood matrix so users can be sure that they will behave like the patient material.

HbA1c testing has in the past been performed in central laboratories using high-throughput immunoassay systems. However, hospitals and smaller clinical settings are increasingly regarding HbA1c as a POC test. This changes the instrumentation needs, regulatory requirements, and staff training levels. “The HbA1c control’s 21 days of room-temperature stability should encourage the introduction of point-of-care testing of HbA1c, just as the introduction of the Dropper Plus product encouraged point-of-care urine dipstick testing nearly 20 years ago,” says Andrew Schaeffer, R&D scientist, Quantimetrix Corp.

Schaeffer describes the enhanced open-vial stability as the control’s best feature. The control’s open-vile stability means less expired control material discarded, resulting in lower laboratory costs.

THE FUTURE OF DIABETES TESTING: GLYCATED ALBUMIN?

Although HbA1c monitoring has been proven a very accurate and efficient way of measuring blood glucose levels, there are incidences in which it is not the ideal assay to use. Measured HbA1c levels may inaccurately show blood glucose concentration when including patient variables such as race,⁶ abnormal hemoglobin, blood transfusions, hemodialysis, kidney failure, anemia, gestational diabetes, and others. What other options are there for measuring the blood glucose for these populations?

Blood serum albumin, like hemoglobin, is a protein that can be glycated. Unlike HbA1c assays, glycated albumin (GA) is in the blood serum and therefore does not require lysing RBCs. This dramatically reduces the complexity of the assay, since only the blood serum is needed. GA has a shorter half-life than HbA1c—14 to 48 days, compared to about 120 days for RBCs. Therefore, GA gives a more recent “picture” of a patient’s blood glucose level history. Depending on the data needed, this can be a benefit for the health care provider and the patient.

GA can also be used alongside standard HbA1c testing to determine the glycation gap: the difference between the predicted average blood glucose by the two assays. A wide glycation gap indicates that the patient is at greater risk of kidney or coronary artery disease.

The initial test for GA was called fructosamine—it was a nonstandardized and historically problematic assay. The new generation of GA tests is far more specific than the old fructosamine assay.⁷ In May 2011, Diazyme received FDA approval for its Enzymatic Glycated Serum Protein Assay Kit. The assay is a two-part liquid-stable reagent that can be used with various types of automated clinical chemistry analyzers. The enzymatic assay is more specific and accurate in comparison to the current nonenzymatic NBT-based fructosamine test. “Technology has vastly improved with glycated albumin testing,” says Douglas Borses, director of sales and marketing, Diazyme. “Glycated albumin testing in some countries is more common than HbA1c. Japan and China are leading the charge. I’m sure we will start seeing it here as well.”

GA testing also has its limitations. Unlike HbA1c, there is no universally accepted standard reference material. It is therefore essential that laboratories communicate to their clinicians that results for GA assays will be different and more specific than older fructosamine methods.

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Sarah Michaud is a contributing writer for CLP.

REFERENCES

1. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. The Diabetes Control and Complications Trial Research Group. N Engl J Med. 1993;329:977-986.
2. Koenig RJ, Peterson CM, Jones RL, Saudek C, Lehrman M, Cerami A. Correlation of glucose regulation and hemoglobin AIc in diabetes mellitus. N Engl J Med. 1976;295:417-420.
3. Bunn HF, Gabbay KH, Gallop PM. The glycosylation of hemoglobin: relevance to diabetes mellitus. Science. 1978;200:21-27.
4. Lenters-Westra E, Slingerland RJ. Six of eight hemoglobin A1c point-of-care instruments do not meet the general accepted analytical performance criteria. Clin Chem. 2010;56:44-52.
5. National diabetes fact sheet: National estimates and general information on diabetes and prediabetes in the United States, 2011. In: U.S. Department of Health and Human Services CfDCaP, ed. Atlanta; 2011.
6. Selvin E, Steffes MW, Ballantyne CM, Hoogeveen RC, Coresh J, Brancati FL. Racial differences in glycemic markers: a cross-sectional analysis of community-based data. Ann Intern Med. 2011;154:303-309.
7. Shima K, Abe F, Chikakiyo H, Ito N. The relative value of glycated albumin, hemoglobin A1c and fructosamine when screening for diabetes mellitus. Diabetes Res Clin Pract. 1989;7:243-250.