Are Those Glucometer Results Accurate?

VARIABLES AFFECTING GLUCOMETER ACCURACY
Patient and environmental factors
Both patient and environmental factors can interfere with obtaining accurate glucometer results. These include sampling errors, improper storage of test strips, inadequate amount of blood applied to the test strip, improper meter coding, and altitude.¹

Temperature extremes and humidity can denature, inactivate, or prematurely rehydrate enzymes and proteins within the test strip.¹ GO meters can overestimate glucose levels at low temperatures, while GDH meters can produce unpredictable results in increased humidity.¹ The detector portion of the meter is composed of electronics and should be protected from temperature extremes and excessive moisture as well.¹

In high altitude, both GO and GDH meters can produce unreliable results, with a tendency to overestimate blood glucose levels.⁸ Another variable confounding the accuracy of glucometer readings at high altitude is the potential for secondary polycythemia, which can result in underestimation of glucose levels.^8,9

Physiologic factors
Physiologic factors that can cause inaccurate glucometer results include hypoxia, abnormal pH, hyperuricemia, jaundice, polycythemia, anemia, peripheral vascular disease, and hypotension resulting in poor perfusion.^1,7,9

Elevated oxygen tension in patients receiving oxygen therapy can falsely lower glucometer results for GO meters, while hypoxia can falsely elevate glucose results for these meters.^1,3

Low pH (< 6.95), such as in diabetic ketoacidosis, falsely lowers glucose readings in GO meters, while a high pH falsely elevates glucose readings.^1,10 Elevated serum uric acid (> 10-16 mg/dL) and elevated total bilirubin concentration (> 20 mg/dL) can cause overestimation of blood glucose levels due to electrochemical interaction at the electrode site in GDH-PQQ meters.¹¹

Polycythemia can result in underestimation of glucose levels, and glucose levels can be overestimated in the setting of anemia.⁹ In anemia, the reduced red blood cell volume results in less displacement of plasma, causing more glucose molecules to be available to react with the enzyme contained in the test strip.¹²

Despite manufacturers’ claims that glucometers are reliable to a hematocrit range of 20% to 25%, clinically significant errors of greater than 20% were observed when the hematocrit level dropped below 34%, which can present challenges if glucometers are used in the ICU.¹³ Mathematical formulas to correct point-of-care glucometer measurements based on the hematocrit level have been proposed and have demonstrated effectiveness in decreasing the incidence of hypoglycemia in critically ill patients treated with insulin.¹²

Medications
Drugs that most commonly interfere with glucometer measurements include acetaminophen (especially at a serum concentration > 8 mg/dL), ascorbic acid, maltose, galactose, and xylose.^1,11 Acetaminophen and ascorbic acid consume peroxide, resulting in falsely lowered blood glucose readings in GO meters. In GDH meters, direct oxidation can occur at the electrode site in the presence of acetaminophen and ascorbic acid, resulting in falsely elevated glucose levels.^6,9,12

Maltose, galactose, and xylose are nonglucose sugars found in certain drug and biologic formulations, such as icodextrin peritoneal dialysis solution, certain immunoglobulins (Octagam 5%, WinRho SDF Liquid, Vaccinia Immune Globulin Intravenous [Human], and HepGamB), Orencia, and BEXXAR radioimmunotherapy agent.¹⁴

The GDH-PQQ meters cannot distinguish between glucose and nonglucose sugars, resulting in either undetected hypoglycemia or a falsely elevated glucose result (up to 3 to 15 times higher than corresponding laboratory results), which can lead to inappropriate medication dosing that results in potential hypoglycemia, coma, or death.¹⁴ Laboratory-based blood glucose assays, the GO, and most GDH-FAD, GDH-NAD, Mut Q-GDH, and hexokinase test strips do not have the potential for cross-reactivity from sugars other than glucose.^4,14

It should be noted that in the United States, most GDH-PQQ test strips are no longer manufactured for home glucose testing. However, it is important to review the product insert contained in the test strip box for verification of the specific enzymatic methodology used in the test strip.^4,5

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