Most nurses, or even lay individuals with a family history of diabetes, consider themselves experts on blood glucose monitoring. Although the procedure is quite simple, there are nuances and intricacies involved in the process. This article is designed to break down the complexities of the blood glucose testing procedure by reviewing terminology, alternate testing sites, and limitations, and providing educational pearls.
Defining the terms
Finger-stick blood glucose monitoring is one of the most common point-of-care orders in the hospital setting and one of the few quantitative tests a patient can perform on his or her own. First, let's start with the terminology related to blood glucose testing.
The finger-stick blood glucose test, point-of-care blood glucose monitoring, capillary blood glucose, and bedside blood glucose are terms used to describe the act of using a portable device called a glucose meter or glucometer. Patients with dysglycemia disorders, such as diabetes, are often required to monitor their blood glucose multiple times per day. When a patient performs all of the testing steps, this act is referred to as self-monitoring of blood glucose (SMBG). If the glucose test is performed by a family member or caregiver, the act is referred to as assisted monitoring of blood glucose.
Changes in endogenous hormone concentrations and postmeal carbohydrate breakdown influence blood glucose values. For these reasons, a glucose value needs to be recorded with time and relationship to oral intake.
Fasting blood glucose is a measurement of blood glucose when the patient hasn't consumed caloric intake for at least 8 hours. It's a useful measurement for diagnosis of prediabetes or diabetes, monitoring dosages of basal insulin, and as a baseline for insulin correction. It's also the most appropriate time for alternate site testing, which we'll cover later in this article.
Two-hour postprandial blood glucose, as the name implies, is a blood glucose value collected exactly 2 hours after starting a meal. This value is extremely important in the management of diabetes and indicates if the appropriate type and quantity of insulin was administered before the meal.
Random blood glucose is a measurement of blood glucose without regard to caloric intake and refers to a value that can be taken at any time. This value is useful if a patient isn't feeling well and will provide feedback for hyper- or hypoglycemia. In patients without diagnosed dysglycemia, abnormal random blood glucose values indicate the need for further glucose testing. Random blood glucose testing shouldn't be used as a guide for administering ordered insulin unless a patient is using an insulin pump.
Alternate testing sites
Essentially, a superficial glucose test can be performed anywhere blood can be obtained from a capillary site. The finger is the most common site because of the concentration of capillaries and the accuracy of the sample. However, finger-stick blood glucose checks can become painful when testing is required multiple times a day.
To ease testing discomfort, numerous manufacturers offer an alternate testing site lancet attachment with their standard meter. Alternate testing sites refer to any place on the body other than the fingertips. The most common sites are the forearm, palm, and thigh. The upper arm and calf have also been studied as alternate testing sites.
Often, little education is provided about alternate testing sites, but it's important for us to provide this education to our patients. Always instruct the patient that the palm of the hand and fingertips provide the most accurate and current snapshot of blood glucose. Explain that if the patient isn't feeling well or may be dosing insulin based on the glucose value, the finger-stick site is the best choice.
The forearm and thigh are appropriate alternate sites; however, there is a lag time of 20 to 35 minutes. This means that if the patient tests his or her blood glucose using blood from the forearm, the value obtained isn't current and reflects the blood glucose 20 to 35 minutes in the past.
When a patient is taking oral diabetes medications and generally has well-controlled blood glucose, alternate testing sites may be used to replace some finger-stick testing. Instruct the patient that the best time of day to use alternate site testing is first thing in the morning when blood glucose levels are generally stable.
Alternate site testing isn't recommended for patients with hypoglycemia unawareness. Also, teach patients to avoid alternate testing sites when they've just exercised, taken insulin, feel like they may have a low blood glucose level, have been ill, or are about to drive.
Blood glucose testing procedures vary per hospital protocol and equipment. The procedure described in this article is a reference for patient education in the clinic or upon discharge from the hospital. Additional steps for calibration and sanitation may be required.
First, instruct the patient to wash and dry his or her hands. This author recommends that patients use soap and water instead of alcohol swabs when possible. This is because the alcohol can dry out fingertips, delay healing of the puncture site, and increase the risk of infection. However, if a sink isn't available, an alcohol swab is acceptable.
Cleansing the site is necessary for two reasons: to remove any substance that might be on the finger to prevent an inaccurate reading and to prevent infection. It's important to have a dry surface because if fluid is present, the sample may be diluted and provide a false low reading.
The rest of the procedure is highly individualized based on the meter and lancet device. Essentially, the next step is to prick the testing site with the lancing device and add a drop of blood to the testing strip. The meter will provide a value within seconds.
Know the limitations
Glucose monitoring is a valuable asset for patients striving for optimal glucose control. The practice is easy, portable, and nearly takes the guesswork out of diabetes management. However, we must remember that there are limitations.
Glucometer accuracy guidelines have been developed by the International Organization for Standardization. Its guidelines state that for glucose levels of less than 75 mg/dL, a meter should read within 15 mg/dL of a known sample; for glucose levels of greater than 75 mg/dL, the values should read within 20% of a reference sample. To be considered “accurate,” a meter should meet stated targets at least 95% of the time.
Erroneous glucose results actually occur quite often. The most common sources are due to operator error and involve the use of expired test strips, improper coding, and application of too little or too much blood. Another significant source of operator error is the use of testing strips exposed to changes in temperature, humidity, and altitude. Acetaminophen, ascorbic acid, and dopamine can also interfere with glucometer results. The FDA reported adverse events, including three deaths, caused by overtreatment of false hyperglycemia caused by an interaction between medications containing maltose and meter test strips.
Several medical conditions affect blood glucose monitoring. For example, severe hypotension causes decreased peripheral blood flow and may impair the quality of the capillary blood sample. Due to hematocrit abnormalities, some meters indicate false results with anemia and polycythemia. Other conditions, such as increased uric acid concentrations and high triglyceride levels, can also alter blood glucose results.
As with any invasive medical procedure, blood glucose monitoring has the potential to expose both the healthcare provider and patient to blood-borne pathogens. The CDC reports 15 known outbreaks of hepatitis B virus infections in the last 10 years directly due to inappropriate blood glucose testing.
To protect yourself and your patients, wash your hands and don gloves before every glucometer use. The CDC recommends one lancet device per person. In the hospital environment or community health fair setting, disposable lancet devices are required. The CDC also recommends one glucometer per person and disinfection if the same glucometer is used for multiple people.
The importance of education
Education is the most important medical intervention in the management of diabetes. When providing education on SMBG, it's important that the patient understands how his or her blood glucose readings are used.
This author had a patient with well-controlled diabetes who took only oral antiglycemic agents, ate healthy meals, and exercised regularly. His concern was that the only input he received from his SMBG was a sore finger. He explained that the reading didn't alter his behavior and had no benefit. It may be obvious what talking points are necessary for patients with uncontrolled diabetes, but what points can healthcare providers use to assist all patients with diabetes?
An excellent education starting point is to discuss how the act of checking blood glucose has demonstrated a reduction in A1C levels and increased medication adherence for noninsulin-dependent patients. Also, the blood glucose logbook serves as a valuable tool for the patient and the management team to personalize the care plan.
The symptoms of hypoglycemia, hyperglycemia, and euglycemia are highly individualized for each patient. Use of SMBG helps patients identify and recognize their glycemic state by allowing them to compare their specific symptoms with a glucose value.
With appropriate education, patients can use SMBG to self-implement interventions based on blood glucose values, such as increasing noncaloric beverage intake and physical activity for hyperglycemia or choosing the best treatment for hypoglycemia.
For example, a patient may eat a fun-size candy bar when his or her blood glucose nears 60 mg/dL. Teach this patient that although this treatment has the appropriate number of carbohydrates, it isn't the best choice due to the high fat content, which slows glucose absorption.
When providing diabetes education, take into consideration that some patients and family members may become offended when referred to as “diabetic.” There's an increasing trend in the literature to use “person with diabetes.” Leading diabetes forums indicate that some patients have a clear preference for the use of “person with diabetes” versus “diabetic” and other patients have no preference. Start out using “person with diabetes” and, as with other medical terminology, adjust to lay terms if it increases a patient's comfort or understanding.
Keep it simple
Although blood glucose testing may seem simple, there are always limitations, complications, or areas for improvement. As nurses, it's important to ensure that our patients are following the latest guidelines and receiving appropriate education for any and all procedures they may undergo. Remember, simple doesn't always mean uncomplicated!
Ms. E is an 87-year-old woman with type 2 diabetes and hypertension. She has become confused over the past few months and her concerned daughter brought her to the hospital after Ms. E fell down a few stairs. The ED physician diagnoses Ms. E with vertigo and recommends an observation admission.
Ms. E's daughter is her caregiver and stays with her at the hospital. Ms. E usually eats her lunch at home around 11 a.m., but when her food tray isn't delivered, her daughter gives her a leftover banana muffin from breakfast. Shortly after noon, the unlicensed assistive personnel (UAP) brings Ms. E her lunch tray and performs a bedside point-of-care finger-stick blood glucose test. The reading is 285 mg/dL, which the UAP promptly reports to Ms. E's clinical nurse. The nurse uses the prescribed correction scale and administers rapid-acting insulin based on the blood glucose test. Shortly after lunch, Ms. E becomes nauseated and gets up to use the restroom; she becomes dizzy and falls. The hospitalist team attributes her inpatient fall to the patient's history of vertigo.
As a nurse reading this scenario, it's easy to see that other factors may have contributed to Ms. E's fall. Perhaps her blood glucose was low after an insulin dose calculated on a postmeal reading and the episode of hypoglycemia then caused the nausea and underlying vertigo.
This scenario illustrates how the improper use of a finger-stick blood glucose test can complicate a patient's condition. If the nurse knew the blood glucose value reported was higher due to the patient eating, would her actions of administering insulin have been different?
The following is a clinical example of a patient who didn't wash his hands before checking his blood glucose.
Mr. J, who has type 1 diabetes and is on an insulin pump, is eating grapes when he suddenly feels tired and nauseated. He gets out his glucometer, quickly lances his finger, and obtains a blood glucose value of 350 mg/dL. Mr. J questions his results, decides to wash his hands, and retests before prompting his insulin pump to deliver. His actual value is 49 mg/dL. There was fructose on his fingers from the grapes that caused a false high blood glucose value. His symptoms were due to hypoglycemia, not hyperglycemia.
If Mr. J hadn't questioned his results, he could have experienced serious adverse reactions.
- Finger-stick blood glucose test, point-of-care blood glucose monitoring, capillary blood glucose, and bedside blood glucose are terms used to describe the act of checking blood glucose levels using a glucometer.
- Self-monitoring of blood glucose, or SMBG, is when a patient performs all of the steps of glucose testing him- or herself. If a family member helps the patient, this is called assisted monitoring of blood glucose.
- Fasting blood glucose is a blood glucose value taken when a patient hasn't consumed any calories for at least 8 hours.
- Two-hour postprandial blood glucose is a blood glucose value collected exactly 2 hours after starting a meal.
- Random blood glucose is a measurement of blood glucose without regard to caloric intake and refers to a value that can be taken at any time.
did you know?
The first glucometer was the Ames Reflectance Meter, which appeared in the late 1960s. It was a 3-lb device that performed merely an approximation of blood glucose levels by comparing variations of blue to a corresponding color chart. The early 1980s saw the evolution of the glucose meter, with changes in shape, size, and availability without a prescription. Over the past 2 decades, meters have become more accurate and smaller in size.