Specimen Collection: Blood Glucose (Ambulatory)
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Failure to follow manufacturer guidelines pertaining to glucose meter use may cause inaccurate results.
Do not milk the patient’s finger or wick blood onto the reagent strips; this may cause inaccurate results.
Failure to recognize inaccurate results can lead to errors in management and death.
Take extra care with a patient who takes medications that increase the risk for bleeding.undefined#ref5">5
Blood glucose monitoring reveals individual patterns of blood glucose changes to aid with meal and activity planning and medication timing. Point-of-care capillary blood glucose testing also allows for a quick response to episodes of high blood glucose (hyperglycemia) or low blood glucose (hypoglycemia).
Obtaining capillary blood by skin puncture is an alternative when venipuncture cannot be performed to reduce the frequency of venous needlesticks and for self-management of diabetes mellitus. The procedure is less painful than venipuncture, and the ease of the skin puncture method makes it possible for patients and families to perform this procedure.
Point-of-care measurement of blood glucose requires obtaining a drop of capillary blood by skin puncture using a single-use, auto-disabling lancet and applying a drop of blood to a specially prepared chemical reagent strip. After the drop of blood is applied to the reagent strip, a reflectance meter provides a measurement of the blood glucose level.
Meters report a wide range of blood glucose values. If a value falls outside of a preset range, the meter reads "low" or "high." Because a low or high reading usually occurs only when blood glucose is in an extreme range, either of these readings must be treated as an emergency. Normal adult blood glucose levels (preprandial) typically fall in the 80 to 130 mg/dl range.2 Less than 70 mg/dl is hypoglycemic, and more than 130 mg/dl is hyperglycemic.1,2 Normal values may vary by age and may depend on the patient’s physical stressors and activity, mealtimes and foods consumed, insulin administration, and medications.
Meters may differ in several ways, including overall size, amount of blood needed for each test, testing speed, ability to store test results in memory, cost of the meter, and cost of reagent strips.6 Some meters recommend wiping away the first drop of blood with gauze and using the second drop for the test, whereas others recommend using the first drop of blood. For accurate results, the health care team member must follow the manufacturer’s instructions. Some meters are voice interactive, which is helpful for patients who have visual impairments. Some meters have memories that record multiple glucose readings for comparison over time.
Additionally, alternative blood glucose monitoring devices are available. Some meters allow for an alternative puncture site, including the forearm, palm, and thigh. Continuous interstitial glucose meters use a very small, fine biosensor inserted through the abdomen or the back of the arm that transmits continuous readings of interstitial glucose levels to a monitor or a computer (Figure 1). These systems support the patient with diabetes mellitus who requires assessment of glucose trends and patterns.6
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Rationale: Hand hygiene promotes skin cleansing and vasodilation at the selected puncture site. Handwashing establishes practice for the patient when the test is performed at home. A patient who has just eaten may have sugar on the hands, which would produce a false high reading.
Rationale: The code on the test strip vial must match the code entered into the glucose meter. Expired strips are not guaranteed to give an accurate reading. Tightly sealing the cap protects the strips from accidental discoloration from exposure to air or light.
Rationale: Some meters are activated when the reagent strip is inserted and therefore do not have an on-off switch.
Rationale: Some devices must be calibrated; others require the timer to be zeroed. Each meter is adjusted differently. Calibration ensures an accurate reading.
Rationale: Some devices communicate patient information into laboratory records or the electronic health record using a unique identifier.
Rationale: Alcohol from the swab may cause blood to hemolyze.
Rationale: Using a single-use, auto-disabling device reduces the possibility of accidental needlesticks, preventing exposure to blood-borne pathogens.
Rationale: The first drop of blood may be contaminated with the alcohol used for disinfection, which may provide an inaccurate result. Newer meters no longer require the first drop to be wiped away.
Always follow the manufacturer’s instructions for specific directions because all meters are slightly different.
Rationale: An adequate-size droplet is needed to activate the meter and obtain accurate results. Excessive squeezing of tissues during blood sample collection may contribute to pain, bruising, scarring, hematoma formation, or dilution of the sample with serous fluid.6 Reusing the same puncture site allows blood that is already clotting to interfere with results. Different meters require different amounts of blood. As blood enters the strip, the glucose device may signal if more blood is required or enough blood is obtained.
Rationale: The blood glucose test result appears on the screen in mg/dl. Some devices signal when the test is completed.
Abnormal values must be evaluated immediately and appropriate treatment initiated per the organization’s practice.
Rationale: The blood glucose test result assists with identifying trends and patterns in glucose levels and is useful for the management of insulin therapy and corrective management.4
Centers for Disease Control and Prevention (CDC). (2011). Injection safety: Infection prevention during blood glucose monitoring and insulin administration. Retrieved May 23, 2023, from https://www.cdc.gov/injectionsafety/blood-glucose-monitoring.html (classic reference)*
*In these skills, a “classic” reference is a widely cited, standard work of established excellence that significantly affects current practice and may also represent the foundational research for practice.
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