Blood glucose monitoring observes for patterns in the fluctuation of blood glucose (sugar) levels that occur in response to diet, exercise, medications, and or pathological processes associated with blood glucose fluctuations such as diabetes. Unusually high or low blood glucose levels can potentially lead to acute and or chronic, life-threatening conditions. Blood glucose level (BGL) or blood sugar level (BSL) monitoring undertaken in the home/community are often referred to as capillary blood glucose (CBG) tests, while blood glucose tests carried out at clinical facilities may include CBG, and (plasma glucose) venous blood tests.
Most food products contain complex carbohydrates which are broken down to supply energy to the cells in our body. Food containing carbohydrates once ingested is broken down in the gastrointestinal system into simpler sugars such as glucose. In the small intestine, glucose molecules are absorbed into the bloodstream and transported to cells across the body and to the liver. Insulin is produced by the beta cells in the pancreas in response to elevated blood glucose levels. In the postprandial phase, insulin facilitates the transportation of glucose from the bloodstream into cells. Further, insulin enables the liver to inhibit gluconeogenesis, and facilitates the storage of glucose in the form of glycogen (glycogenesis) and fats (de novo lipogenesis (DNL)) which serve as short- and long-term stores of energy respectively. The human body attempts to maintain homeostasis in blood glucose levels (4 to 6 mmol or about 72 to 108 mg/dL). This is influenced by the functional capacity of the beta-cells of the pancreas, cellular (skeletal muscles, liver, and adipose tissue) sensitivity to insulin.
In conditions like diabetes, there is either a lack of insulin or the body does not appropriately respond (otherwise called insulin resistance) to the actions of insulin (to facilitate cellular uptake of glucose or storage of excess glucose). Dysfunction in production or uptake of insulin can potentiate impaired blood glucose levels. Patients with impaired blood glucose levels and impaired fasting blood glucose are at high risk for developing diabetes. Patients diagnosed with diabetes if their BGL’s are high. Some organs such as the brain, kidneys, liver, and red blood cells do not have insulin receptors and do not require insulin for the uptake of glucose. These organs, especially the brain, are significantly affected by (acute, chronic, and/or recurrent) drops in blood glucose levels and are associated with significant morbidity.
Insulin is used in the management of type 1 diabetes and some cases of type 2 diabetes. Insulin therapy has a well-known adverse side effect of hypoglycemia if its administration is not managed effectively. Patients with insulin-dependent diabetes will benefit from regular blood glucose monitoring. Regular daily blood glucose monitoring is recommended for those with diabetes and insulin therapy.
Blood glucose monitoring may support the diagnosis and management of the client with impaired glucose metabolism or diabetes. Regular monitoring of blood glucose levels is not recommended for patients with type 2 diabetes on oral antidiabetic drugs and or dietary management. However, blood sugar monitoring may be warranted when the treating team is titrating oral hypoglycaemic medications to manage clients with medications (example: sulfonylureas) known to cause hypoglycemia.
Capillary Blood Glucose Test
A blood drop sample is usually collected from a fingertip prick.
Blood samples can also also be sourced from alternate sites such as the earlobe, heel, forearm, palm. Alternate site testing provides similar results to finger-prick testing, especially in the fasting and two-hour post meal times. Using alternate sites may be less painful but may need a deeper lance. Check with the manufacturer of the glucometer if the machine may be used for alternate site testing.
Equipment used includes a lancet used to prick the skin, a glucometer, and test strips. Glucometers have a range of features with modern smart machines requiring a very small sample of blood (from 0.3 to 1 microL), have Bluetooth capabilities that synchronize data with paired applications (apps) on smartphones. These machines and apps record data and provide trends in glucose measurements undertaken. Further, some apps also provide options to record diet and medications used, type of physical activity undertaken, which may be useful to the health care practitioner when managing the care plan for the client with diabetes.
Advantages: Small blood sample, range of alternate sites capable of testing, short testing time, large display on glucometer, less painful than venipuncture.
Disadvantages: Manufactures often provide low cost or subsidized glucometers but sell testing strips and accessories at a significant profit margin. The test strips are expensive, time-limited (short expiry dates), and are affected by a range of variables including temperature, humidity, size, and quality of blood sample. Accuracy of the results is dependent on the clinical presentation of the client and may not be very reliable in clients with hypoglycemia, anemia, altered hematocrit, hypotension, or those who are critically ill. Older machines may need calibration with test strips, and results could be compromised if the calibration is not undertaken appropriately.
Venous (Plasma) Blood Sample
Venous blood is collected via venipuncture, and the sample processed in a commercial-grade laboratory with appropriate sophisticated quality control checks.
Advantages: Accurate measurement of blood glucose is superior to the capillary blood glucose test. However, this is dependent on the laboratory meeting established industry standards.
Disadvantages: Painful procedure, risk of local tissue damage, unsuitable for frequent specimen collection.
Continuous Glucose Monitoring (CGM)
Flash blood glucose monitoring (continuous interstitial fluid glucose monitoring): This test involves applying a water-resistant disposable sensor on the back of the upper arm or abdomen. The sensor can remain on the patient for 3 to 14 days, depending on the product. The sensor can be scanned with a reader, which displays the patient's current and trends in the last 8 hours of interstitial fluid glucose levels. CGM machines can store 90 days of glucose data. Data from the CGM device could be shared with (family and care provider) via a smartphone device application, and these devices are often capable of sending alarms or messages of alerts, including hypoglycemia. Some CGM's can work with compatible insulin delivery devices and can stop insulin delivery if the machine predicts and or recognizes a drop in BSL. Some older CGM machines do require up to 2 finger-prick tests each day for purposes of calibration, however, the more recently introduced devices do not require this calibration.
Advantages: In patients requiring insulin therapy (both type 1 diabetes and in patients with type 2 diabetes requiring intensive insulin therapy and or sulfonylureas, flash monitoring has been demonstrated to be cost-effective when compared to CBG self-monitoring of blood glucose (SMBG). Interstitial glucose measurements are recorded as frequently as every 5 minutes every hour, which has the benefit of monitoring for hypoglycemia during sleep at night.
Disadvantages: Glucose is first seen in blood before it is seen in the interstitial fluid, which the CGM measures hence may not always be a reliable indicator in rapidly changing blood glucose levels. The high cost of sensors and machines (approximately $5000 per annum) may not make this a viable option in economically less advantaged clients and communities where health care is not subsidized by insurance or the government.
Capillary Blood Glucose (CBG) Testing
Steps in the procedure of undertaking a capillary blood glucose test with a glucometer.
Wash and dry hands and site (if the site is other than the hand) is to be tested.
Skin or site preparation, if required.
Note: The recommended site on palm: Side of distal ends of fingertips to minimize injury to the bone. Avoid the little finger as the tissue may not be deep enough to prevent injury to the bone. Avoid the index finger and thumb as these are highly sensitive areas compared to other fingers. Avoid the arm if an intravenous infusion is underway or is the side of the body where a recent mastectomy, if any, was performed. Heel stick stab, if done, can be more painful and may require resampling. Consider pain management in the neonate. The preferred site on the heel is the lateral or medial plantar surface for babies up to one year of age.
Prime the lancet to no more than 2.0 mm to minimize the risk of bone injury.
Remove the glucose testing strip without touching the sensor tip from the container. Insert glucose testing strip into the glucometer; this often leads to the glucometer turning itself on.
Firmly apply lancet to the site of sample collection.
Release the trigger on the lancet to pierce the skin.
Recommendations are to wipe away the first drop of blood with clean gauze or tissue as this drop of blood may contain intracellular or interstitial fluid, or is hemolyzed, both of which could affect the blood sample.
Gentle downward pressure applied close to the puncture site may facilitate blood flow and collection of the second drop of blood.
Collect the second drop of blood as it forms by touching the tip of the glucose testing strip.
Place glucometer down and cover the site of skin puncture with a clean tissue. Pressure may need to be applied to stop further bleeding from the puncture site.
The machine normally provides a result at this stage unless there have been errors in collection; for example, insufficient sample, low battery, wrong code, or the machine times itself out. If an error displays on the glucometer, troubleshoot as appropriate.
Wash hands and replace equipment in storage bag container.
Make a note of test results relative to diet, exercise, and/or medication use as appropriate.
Results, Reporting, Critical Findings
Blood glucose is measured in mmol/L (millimoles per liter) or mg/dL (milligrams per decilitre)
Normal range: 4 to 6 mmol or about 72 to 108 mg/dL.
Lab-based Blood Glucose Testing
Lab-based testing is required for the appropriate diagnosis of diabetes.
Impaired fasting glucose range: 5.6 to 6.9 mmol per L, or 100 to 125 mg/dL
Impaired (oral glucose tolerance test) glucose tolerance range at two hours post 75gram oral glucose ingestion: 7.8 to 11.0 mmol, or 140 to 199 mg/dL.
Further testing may involve an oral glucose tolerance test to confirm the diagnosis. Advice the client to eat and drink over 150 grams per day of carbohydrate foods for three days. The client will need to fast overnight for at least 8 to 16 hours before the test. A fasting blood sample is collected, and a sweet drink containing 75 grams of glucose is given to the client after the fasting blood sample collection. A further blood sample is collected at two hours following the consumption of the glucose drink.
Oral glucose tolerance test: Glucose tolerance range at two hours post 75-gram oral glucose ingestion: ≥11.1 mmol, or ≥200 mg/dL.
Random venous blood glucose of at or above 11.1mmol/L (≥200 mg/dL), or fasting blood glucose at or above 7 mmol/L (≥126 mg/dL) on two or more separate occasions indicates the client is likely to have diabetes.
HBA1c: Glucose molecules tend to attach to hemoglobin. This test interprets the percentage of glucose molecules that combine with hemoglobin to form glycated hemoglobin. Once glucose molecules combine with the hemoglobin, the merger (glycated hemoglobin) remains for the life of the red blood cell, which is, on average, around 60 to 120 days. Analyses of the red blood cell and its attached glycated hemoglobin reveals the average blood glucose levels in the client over those 2 to 4 months.
Normal HBA1c: 3.5 to 6 per cent (15 to 42 mmol/mol).
A result of glycosylated hemoglobin (HbA1c) >6.5% confirms the presence of diabetes. Pharmacological intervention is required in clients with HBA1c levels greater than 7.0%. This test is currently recommended to be undertaken to diagnose and provide appropriate ongoing management of the diabetic client.
Note: There is a small but significant difference between capillary blood glucose measurements undertaken at home and the venous or arterial blood sampling done in clinical facilities. Care must be taken when using the results from capillary tests and venous tests either exclusively or together.
Blood glucose monitoring is an essential part of case management in clients with diabetes. Having very high or very low levels of blood glucose could impair cellular function and may be lethal if not managed appropriately. Stress-related hyperglycemia may also be seen in clients who have experienced an acute medical and or surgical event.
Etiology of hyperglycemia includes:
- Inadequate insulin administration in clients with type 1 diabetes,
- Insulin resistance with type 2 diabetes which inhibits glucose metabolism
- Stress-related experiences (such as critical illness) inducing glycogenolysis and gluconeogenesis)
- Client experiences of the dawn phenomena where there is a surge in hormones between 0400 and 0500 that cause a spike in blood glucose levels.
Symptoms of hyperglycemia include polyuria (increased and frequent urination), polydipsia (increased thirst), blurred vision, headache and fatigue, and glucosuria. Acute symptoms of hyperglycemia are not usually seen at levels below 14 mmol/L or 250 mg/dl.
Episodes of hyperglycemia for an extended period leads to either diabetic ketoacidosis or hyperglycemic hyperosmolar state.
If left untreated hyperglycemia may cause the client to go into a state of ketoacidosis where the body begins to process fats (gluconeogenesis) to produce the energy required for cellular function. This could be as a result of a lack of insulin produced by the pancreas (as seen in type 1 diabetes).
Diabetic ketoacidosis is a life-threatening scenario where a client could potentially go into a state of coma from a lack of insulin production and clients may have symptoms of fruity odor (from the ketones being produced in the body as a result of fat metabolism), ketonuria, tachypnea and or shortness of breath, nausea, and vomiting.
In the hyperosmolar state, a rare condition is seen in clients with type 2 diabetes, the body in its attempt to get rid of the high glucose levels in the blood produces large amounts of urine causing life-threatening dehydration and potentially coma. Both diabetic ketoacidosis and hyperosmolar state require emergent management to reduce elevated blood glucose levels with insulin therapy.
Long term high blood glucose levels could potentially delay wound healing, damage nerves (peripheral neuropathy) and end-organs such as the eyes (diabetic retinopathy), kidneys (renal failure), the brain (stroke), and the heart (myocardial infarction).
Symptoms of hypoglycemia are seen when low blood glucose levels deprive the body of essential fuel to sustain life.
Causes of hypoglycemia include taking too much insulin, and or not enough carbohydrates or inappropriate exercise in relation to diet and or insulin intake.
Clients present with symptoms of confusion, sweating, tachycardia, blurred vision, feeling lightheaded, being clumsy, or may have seizures. Often clients do not recognize the onset of symptoms of hypoglycemia which may put them at high risk of injury either while undertaking regular activity (such as driving) or while asleep.
Emergent treatment to restore normal blood glucose levels is imperative as certain organs (e.g. brain) do not store glucose and need a constant supply of blood glucose to sustain life. Antidiabetic therapy needs re-evaluation when BSL falls below 5.6 mmol/liter (100 mg/dl) and modification of antidiabetic therapy is essential if BSL drops below 3.9 mmol/liter (70 mg/dl).
Clients across the life span with diabetes have varying clinical presentations (and underlying clinical pathologies linked to diabetes). They may not always report the effects of hypoglycemia or hyperglycemia which should involve monitoring for other signs and symptoms. Clients with renal insufficiency are at risk of hypoglycemia as the kidneys are primarily responsible for metabolizing exogenous insulin.
Glycemic care in the clinical setting
For appropriate glycemic control in clients with diabetes in non-critical care settings, capillary blood glucose testing is the recommended method of testing. In clients who are capable of eating, blood glucose testing is recommended before meals and at bedtime, and every 4-6 hours in clients receiving enteral feeds and or are nil by oris (NPO). All hospitalized patients will benefit from an initial screen for blood glucose irrespective of a history of diabetes. The use of glucose management protocols, with nurse-initiated treatment protocols, is ideal for the management of hypoglycemia in the hospital setting.
Community and rehabilitation setting based care.
Clients need education on the importance of regulating diet, exercise and medications to prevent acute and or chronic complications that were seen in extreme blood glucose fluctuations in conditions like diabetes. Further, clients need specific education to test for blood glucose, including handwashing before testing appropriately, calibrating glucometer if required, using the lancet, acquiring a blood sample, interpreting results, reporting and following up on results.
Enhancing Healthcare Team Outcomes
Managing diabetes to improve patient outcomes requires a complex multidisciplinary approach. Blood glucose monitoring is a critical measurement of ongoing diabetes management. However, these blood test results should be viewed considering the complex socioeconomic disease process impact diabetes has, including on the various body systems but not limited to metabolic syndrome, micro, and microangiopathies, adverse (acute and or chronic) effects of hypoglycemia and hyperglycemia. Implementation of a systematic process aimed at managing altered blood glucose levels (as in diabetes) requires input and active collaboration with the client as a consumer, endocrinologists, diabetes nurse educators, pharmacists, clinical nurse specialists, dieticians, and data analysts.