Hemoglobin (Hb) A_1c With GlycoMark® Reflex

Serum or plasma and whole blood, refrigerated

1 mL serum or plasma and 3 mL whole blood

0.75 mL serum or plasma and 1 mL whole blood (Note: This volume does not allow for repeat testing.)

Red-top tube or gel-barrier tube or EDTA plasma tube and lavender-top (EDTA) tube or green-top (lithium heparin) tube or gray-top (sodium fluoride) tube or tan-top (K2 EDTA) tube

GlycoMark® testing provides an estimate of the patient's postmeal glucose over a one- to two-week period, making it ideal for intermediate term monitoring of glycemic control in diabetic patients. GlycoMark® testing can also help monitor the effectiveness of therapeutics targeting postprandial glucose (PPG),^1,2 and it is a useful adjunct to routine A1c testing because it responds more rapidly and sensitively to hyperglycemia than A_1c.^1,2

Hb A_1c testing provides an estimate of the patient's average blood glucose over a period of two to three months. Hb A_1c testing helps assess the long term diabetic control for individuals with diabetes mellitus.

Individuals using INVOKANA® may demonstrate low levels of 1,5-AG. 1,5-AG blood levels are falsely lowered by the diabetes drug INVOKANA® which prevents reabsorption of 1,5-AG in the kidneys. INVOKANA® belongs to new class of diabetes medication known as sodium-glucose cotransporter 2 (SGLT2) inhibitors, which block reabsorption of glucose in the kidneys, and other SGLT2 inhibitors may have the same effect. INVOKANA® is a trademark of Janssen Pharmaceuticals Inc.

Persistently positive urinary glucose levels, or oxyhyperglycemia after gastrectomy, may result in a low 1,5-AG value. Low values have also been observed in pregnancy, terminal stage renal failure, dialysis patients, advanced cirrhosis, and prolonged incapability of oral ingestion of food. Abnormal values have also been noted in individuals with abnormal glomerular filtration rates.^3,4

For some patients with severe hyperglycemia, the internal pool of 1,5-AG may tend to remain depleted as a result of persistent glucosuria. In these cases, measurements of 1,5-AG may be less indicative of initial recovery following initiation of antidiabetic treatment.

1,5-AG values may be increased when some Chinese medicines, such as Polygala Tenuifolia and Senega syrup, are administered. Values may also be increased during intravenous hyperalimentation. 1,5-AG values may be lower in patients undergoing therapy with steroids.⁵

Some alpha-glucosidase inhibitors, such as Acarbose, may potentially reduce 1,5-AG levels due to interference with intestinal absorption of 1,5-AG.

As with all diagnostic tests, GlycoMark® results should be interpreted along with clinical findings and results from other diagnostic methods.

See individual assays. GlycoMark® is a registered trademark of GlycoMark Inc, New York, NY.

GlycoMark®:

• <18 years: Not established

• Adult males: 10.7−32.0 μg/mL

• Adult females: 6.8−29.3 μg/mL

• Glycemic control goal for diabetic patients: >10

Hemoglobin A_1c (percent):

• Normal: <5.7

• Increased risk for diabetes: 5.7−6.4

• Ongoing hyperglycemia: >6.4

• Estimated average glucose:

− Glycemic control for adults with diabetes: <7.0 (ADA)

Note: If A_1c results are between 6.0 and 8.0 (including 6.0 and 8.0), GlycoMark® testing is performed. GlycoMark® reflects postprandial glucose spikes from the previous two weeks, whereas A_1c reflects average glycemic control during the previous three months.

1,5 Anhydroglucitol (1,5-AG) is a naturally occurring monosaccharide found in nearly all foods. Individuals without diabetes and those with diabetes but have well-controlled blood glucose levels <180 mg/dL have detectably high levels of 1,5-AG. When a individual's glucose levels are in a normal range, 1,5-AG is naturally processed by the kidneys and nearly all of it is reabsorbed back into the blood stream by the renal proximal tubules. Individuals with diabetes that have blood glucose level excursion in excess >180 mg/dL can be expected to have low levels of 1,5-AG. In these individuals, excess glucose in the body is reabsorbed first by the kidneys, blocking 1,5-AG reabsorption. The body is unable to maintain a high steady state level of 1,5-AG in blood and tissues.

• Normal or high GlycoMark® values = Normal blood glucose levels

• Low GlycoMark® values = Elevated blood glucose levels or high blood glucose spikes

• Normal levels of glucose produce a normal amount of Hb A_1c. As the average amount of plasma glucose increases, the fraction of Hb A_1c increases in a predictable way. This test serves as an indicator for average blood glucose levels over the previous two to three months prior to the measurement.

• Normal Hb A_1c values = Normal blood glucose

• Higher Hb A_1c values = Elevated blood glucose levels