GlycoMark Test: How it Works, Reference Range, Advantages and Limitations
The GlycoMark test is a simple, non-fasting blood test that measures blood glucose control over a 1 to 2 week period in people with diabetes. 1,5-anhydroglucitol (1,5-AG) is a particular type of glucose-like sugar in your blood which is measured in this test. The higher your blood glucose levels, the lower the amount of 1,5-AG in your blood resulting in lower GlycoMark test value.
With A1C, your score increases when your blood glucose increases, where as your GlycoMark result actually decreases when your blood glucose increases. So, a higher GlycoMark score means better control of diabetes.
Hyperglycemia is a condition where your blood sugar is at levels higher than your body can handle. Spikes in glucose levels followed by drops in glucose levels can occur in this condition.
The goal of diabetes management is to maintain your blood glucose levels by reducing major swings, such as high blood glucose after you eat or low blood glucose after you take your diabetes medication.
The major complications of high glucose levels include kidney disease, retinopathy and cardiovascular diseases. In addition, it can decrease energy, alter your moods, and compromise brain function. Therefore, effective management of diabetes should be done as soon as possible. As GlycoMark test is the only specific indicator of recent hyperglycemic spikes, it can help you in this case.
The GlycoMark test can be used in addition to traditional blood glucose tests, like hemoglobin A1C or fasting blood sugar. A1C scores are inaccurate due to red blood cell anomalies in few cases. Patients whose A1C scores indicate good control of diabetes may suffer significant glucose fluctuations that don't show up in an A1C average. In such cases 1,5 AG can identify specific hyperglycemic peaks, providing detailed, accurate information that can be masked by an average value.
The GlycoMark test works by monitoring 1,5-AG. In diabetes, glucose levels can be persistently high, or they can fluctuate over time. Depending on the level of glycemic control these fluctuations can occur over weeks, days, or hours.
At times the fasting glucose is being well managed, but the patient may still be having episodes of hyperglycemia, referred to as glucose spikes or hyperglycemic excursions, following meals.
HbA1C cannot distinguish between stable glucose levels and glycemic variability characterized by high glucose levels balanced by low levels. The offsetting effect of glucose highs and lows produces an A1C level that could be a wrong assumption of a patient with a stable glucose level.
The GlycoMark test works by monitoring levels of the 1,5-anhydroglucitol (1,5-AG) molecule in the blood. 1,5-AG is stored at a steady state in the tissues and the bloodstream, keeping blood levels high and producing a high GlycoMark score in people who do not have diabetes, and those with diabetes who have well-controlled blood sugars.
1,5-AG is structurally similar to glucose, and it is filtered in the kidneys like glucose. 1,5-AG is filtered through the kidneys and nearly all of it is reabsorbed back into the blood stream in the renal proximal tubules in people who do not have diabetes, and with diabetes with well-controlled blood glucose levels. So, 1,5- AG is kept in the body at high levels when blood glucose is well-controlled.
There is too much glucose in the kidneys in people who have high blood sugars, exceeding approximately 180 mg/dL. The excess glucose is reabsorbed in the renal proximal tubules, blocking 1,5-AG from being reabsorbed. This is because 1,5-AG levels are much lower than glucose levels. Therefore, 1,5-AG is excreted in the urine and decreases in the bloodstream resulting in a lower GlycoMark test result.
The GlycoMark can provide an estimate of the average daily peak glucose level as the test is linked to the renal threshold and is affected by periods of hyperglycemia exceeding the renal threshold.
When 1,5-AG levels are below the reference range, the average daily peak glucose levels can exceed the renal threshold. A large difference between the estimated average daily peak glucose level and the estimated average glucose level may indicate glycemic variability. Glycemic variability is glucose highs balanced by lows which can only be detected by this test.
Lower values indicate a poor glucose control, with more frequent and prolonged glucose values over 180 mg/dL. 10 mcg/mL of 1,5-AG correlates to an average post meal glucose of 185 mg/dL. Values more then 10 mcg/mL indicate glucose on average is below 180 mg/dL.
Greater then 12 indicate glucose on average is below 180 mg/dL. Value of 8 indicate glucose on average is 190 mg/dL. 6 indicate glucose on average is below 200 mg/dL. 4 indicate glucose on average is 225 mg/dL where as value less then 2 indicate glucose on average is greater then 290 mg/dL.
The GlycoMark test is not affected by hemoglobinopathies, such as anemias, sickle cell disease or malaria because it is not a hemoglobin glycosylation marker like HbA1c. The GlycoMark test can also be used as a short term marker of glucose control at all levels of A1C, and can identify the frequency of hyperglycemic excursions.
The GlycoMark test has been tested and found to be unaffected by hemoglobin, triglycerides, bilirubin, glucose, maltose, ascorbic acid, uric acid, urea and creatinine.