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Introduction ⬇

Glucose is formed from carbohydrate digestion and conversion of glycogen to glucose by the liver. The two hormones that directly regulate blood glucose are glucagon and insulin. Glucagon accelerates glycogen breakdown in the liver and causes the blood glucose level to rise. Insulin increases cell membrane permeability to glucose, transports glucose into cells (for metabolism), stimulates glycogen formation, and reduces blood glucose levels. Driving insulin into the cells requires insulin production and insulin receptors. For example, after a meal, the pancreas releases insulin for glucose metabolism, provided there are enough insulin receptors. Insulin binds to these receptors on the surface of target cells such as are found in fat and muscle. This opens the channels so that glucose can pass into cells, where it can be converted into energy. As cellular glucose metabolism occurs, blood glucose levels fall. Adrenocorticotropic hormone (ACTH), adrenocorticosteroids, epinephrine, and thyroxine also play key roles in glucose metabolism.

Categories of diabetes:

  1. Type 1 diabetes (T1D), formerly known as insulin-dependent diabetes or juvenile-onset diabetes, is due to destruction of pancreatic β cells, which leads to deficiency in insulin; it accounts for about 5%–10% of individuals diagnosed with diabetes.

  2. Type 2 diabetes (T2D), formerly known as non–insulin-dependent diabetes or adult-onset diabetes, is a progressive form of insulin deficiency concomitant with insulin resistance that accounts for 90%–95% of individuals diagnosed with diabetes.

  3. Gestational diabetes (GD) is due to a hormone produced by the placenta that makes insulin less effective (known as insulin resistance) and is usually temporary to other causes (e.g., genetic defects [see Chapter 11 for genetic causes]), disease of the pancreas, drug or chemical induced, and so forth.

  4. Due to other causes (e.g., genetic defects [see Chapter 11 for genetic causes]), disease of the pancreas, drug or chemical induced, and so forth.

Prediabetes, also known as impaired glucose tolerance (IGT) or impaired fasting glucose (IFG), is blood glucose levels that are elevated, but not high enough to be termed T2D but, if left untreated, may develop into T2D within 10 years.

Considered a hybrid form of diabetes with features of both T1D and T2D, latent autoimmune diabetes in adults (LADA) is a type of diabetes that is best if diagnosed early in the course of the disease process because of the high risk for developing insulin dependency. It has been found that patients with LADA have adult onset autoimmune activity and decreased insulin secretion that progresses to insulin dependence.

Fasting blood glucose (FBG) is a vital component of diabetes management. The term random/casual is defined as any time of day without regard to time since the last meal. Fasting is defined as no caloric intake for at least 8 hours. Abnormal glucose metabolism may be caused by inability of pancreatic islet β cells to produce insulin, reduced numbers of insulin receptors, faulty intestinal glucose absorption, inability of the liver to metabolize glycogen, or altered levels of hormones (e.g., ACTH) that play a role in glucose metabolism.

In most cases, significantly elevated fasting plasma glucose (FPG) levels are, in themselves, usually diagnostic of diabetes. However, mild, borderline cases may present with normal fasting glucose values. If diabetes is suspected, a glucose tolerance test (GTT) or A1C criteria can confirm the diagnosis. Occasionally, other diseases may produce elevated plasma glucose (PG) levels; therefore, a comprehensive history, physical examination, and workup should be done before a definitive diagnosis of diabetes is established.

Clinical Alert

  1. The National Institutes of Health guidelines endorse diabetic testing of all adults aged 45 years and older every 3 years. The American Diabetes Association (ADA) recommends the following guidelines for testing:

    • Should be considered for all patients at 45 years of age and every 3 years afterward (if results are normal)

    • Should be considered for patients who are overweight or obese (≥25 kg/m2 or ≥23 kg/m2 in patients of Asian descent)

    • Should be considered for women planning pregnancy who are overweight or obese or have one or more risk factors for diabetes

    • Women with GD should have testing every 3 years (lifelong)

    • Patients identified as prediabetic should have testing annually

  2. Diabetes, a group of metabolic disorders, is characterized by hyperglycemia and abnormal protein, fat, and carbohydrate metabolism due to defects in insulin secretions—that is, inadequate and deficient insulin action (insulin resistance) on target organs.

  3. Criteria for diagnosing diabetes:

    1. Symptoms of diabetes plus random/casual PG concentration of ≥200 mg/dL (≥11.1 mmol/L). Random/casual PG is defined as any time of day without regard to time since last meal. The classic symptoms of diabetes include polyuria, polydipsia, and unexplained weight loss, or

    2. FPG ≥126 mg/dL (≥7.0 mmol/L) on at least two occasions (fasting is defined as no caloric intake for at least 8 hours), or

    3. Two-hour PG ≥ 200 mg/dL (≥11.1 mmol/L) during an oral glucose tolerance test (OGTT). The test should be performed as described by the World Health Organization (WHO), using a glucose load containing the equivalent of 75 g of anhydrous glucose dissolved in water, or

    4. Hemoglobin A1c (HbA1c) ≥6.5% (48 mmol/mol). Method used for testing should be National Glycohemoglobin Standardization Program certified and standardized to Diabetes Control and Complications Trial assay.

      1. In the absence of unequivocal hyperglycemia with acute metabolic decompensation, these criteria should be confirmed by repeat testing of b through d on a different day. OGTT is not recommended for routine clinical use.


Source: American Diabetes Association. (2020). Standards of medical care in diabetes—2020. Diabetes Care, 43(suppl 1), S89–S212. http://care.diabetesjournals.org/content/diacare/suppl/2019/12/20/43.Supplement_1.DC1/Standards_of_Care_2020.pdf

Normal Findings ⬆ ⬇

FPG, adults: ≤100 mg/dL or ≤5.6 mmol/L

Fasting, children (2–18 years): 60–100 mg/dL or 3.3–5.6 mmol/L

Fasting, young children (0–2 years): 60–110 mg/dL or 3.3–6.1 mmol/L

Fasting, premature infants: 40–65 mg/dL or 2.2–3.6 mmol/L

Clinical Alert

Critical values for fasting blood glucose (FBG): 40 mg/dL (2.22 mmol/L) may cause brain damage (women and children), 50 mg/dL (2.77 mmol/L) (men); >400 mg/dL (>22.2 mmol/L) may cause coma

Procedure ⬆ ⬇

  1. Draw a 5-mL venous blood sample from a fasting person or a random PG (FPG) (any time of day). In known cases of diabetes, blood drawing should precede administration of insulin or oral hypoglycemic agent. Observe standard precautions. Serum is acceptable if separated from red cells within an hour. A gray-topped tube, which contains sodium fluoride, is acceptable for 24 hours without separation.

  2. Self-monitoring of capillary glucose by the person (or healthcare provider) with diabetes can be done by finger stick blood drop sampling several times per day if necessary. Several devices are commercially available for this procedure; they are relatively easy to use and have been established as a major component in satisfactory diabetes control. Calibration of monitoring devices should be done on a regular basis (Figure 6.1).

  3. Noninvasive methods using skin pads and a smart phone application to check blood glucose level are now available for self-monitoring that eliminate the dreaded finger-prick test. Other options include a watch-like device that provides glucose measurements while wearing it and sensor device that is clipped to the ear to obtain a glucose measurement.

Patient Checklist for Self-Monitoring of Capillary Glucose Testing

This list is a general outline. Each brand of meter has its own instructions. Read the instructions on each new meter carefully to get accurate results. Know whether the monitor and strips give whole blood or plasma equivalent results.

  1. General instructions:

    1. Make sure hands are clean, dry, and warm.

    2. Clean your finger with an alcohol pad and prick the finger with the lancet when the area is dry.

    3. Squeeze out a drop of capillary blood and wipe with gauze.

    4. Apply SECOND drop of blood onto the test strip or sensor.

    5. Wait for the test strip or sensor to develop.

    6. Compare the test strip to the chart or insert it into the meter.

    7. Safely dispose of the lancet in an approved sharps container.

    8. Record results with date and time.

  2. If T1D is present, also monitor urine for ketones or blood β-hydroxybutyrate for possible dangerous complications such as diabetic ketoacidosis (e.g., during stress or acute illness).

  3. Test more often on days when illness occurs, when the reading is too high, when meal or exercise plans change, when traveling, or if it feels as though the blood glucose level is low.

  4. If concerned about getting accurate results, consult with the diabetes educator or contact the manufacturer to ensure proper use of the monitor.

  5. Several blood glucose meters currently available are approved by the U.S. Food and Drug Administration (FDA), the agency that approves medical devices, for what is called alternate site testing.

  6. Alternate sites (other than fingertips) include forearm, bicep area, palm of hand, between fingers, and sometimes the calf.

  7. Tips for using alternate sites:

    1. Rub the site to be used to check blood glucose vigorously before pricking skin. This increases blood flow to the site.

    2. Use one type of monitor; do not alternate between different monitors. This will help to obtain consistent results.

    3. Consistently use the same alternate site. For example, always use forearms. This will also help to obtain consistent results.

Clinical Alert

A recent warning was published by the FDA, alerting users of portable glucose monitors to be cognizant of the units of measurement displayed; that is, mg/dL or mmol/L. Reporting a glucose value without reporting the unit of measurement could result in an adverse event

Clinical Implications ⬆ ⬇

  1. Elevated blood glucose (hyperglycemia) occurs in the following conditions:

    1. Diabetes: a fasting glucose ≥126 mg/dL (>7.0 mmol/L) or a 2-hour postprandial load PG ≥200 mg/dL (>11.1 mmol/L) during an oral GTT.

    2. Other conditions that produce elevated PG glucose levels include the following:

      1. Cushing disease (increased glucocorticoids cause elevated blood sugar levels)

      2. Acute emotional or physical stress situations (e.g., myocardial infarction [MI], stroke, convulsions)

      3. Pheochromocytoma, acromegaly, gigantism

      4. Pituitary adenoma (increased secretion of growth hormone (GH) causes elevated blood glucose levels)

      5. Hemochromatosis

      6. Pancreatitis (acute and chronic), neoplasms of pancreas

      7. Glucagonoma

      8. Advanced liver disease

      9. Chronic kidney disease (CKD)

      10. Vitamin B deficiency: Wernicke encephalopathy

      11. Pregnancy (may signal potential for onset of diabetes later in life)

  2. Decreased blood PG (hypoglycemia) occurs in the following conditions:

    1. Pancreatic islet cell carcinoma (insulinomas)

    2. Extrapancreatic stomach tumors (carcinoma)

    3. Addison disease (adrenal insufficiency), carcinoma of adrenal gland

    4. Hypopituitarism, hypothyroidism, ACTH deficiency

    5. Starvation, malabsorption (starvation does not cause hypoglycemia in normal persons)

    6. Liver damage (alcoholism, chloroform poisoning, arsenic poisoning)

    7. Premature infant; infant delivered to a mother with diabetes

    8. Enzyme deficiency diseases (e.g., galactosemia, inherited maple syrup urine disease, von Gierke syndrome)

    9. Insulin overdose (unintentional or deliberate)

    10. Reactive hypoglycemia, including alimentary hyperinsulinism, prediabetes, endocrine deficiency

    11. Postprandial hypoglycemia may occur after gastrointestinal (GI) surgery and is described with hereditary fructose intolerance, galactosemia, and leucine sensitivity

  3. According to the ADA criteria, there are four definitive tests for diabetes:

    1. Symptoms of diabetes plus a random/casual PG ≥200 mg/dL (>11.1 mmol/L), or

    2. An FPG ≥126 mg/dL (>6.99 mmol/L; in the absence of unequivocal hyperglycemia, criteria b to d should be confirmed by repeat testing), or

    3. An OGTT with a 2-hour postload (75-g glucose load) level ≥200 mg/dL (>11.1 mmol/L; in the absence of unequivocal hyperglycemia, criteria b to d should be confirmed by repeat testing), or

    4. HbA1c ≥6.5% (in the absence of unequivocal hyperglycemia, criteria b to d should be confirmed by repeat testing)

  4. The classification of diabetes diagnosis reflects a shift to the etiology or pathology of the disease from a classification based on pharmacologic treatment.

  5. IFG or IGT is referred to as prediabetes.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and blood-drawing procedure. Note time.

  2. Tell patient that the test requires at least an overnight fast; water is permitted. Instruct the patient to defer insulin or oral hypoglycemic agents until after blood is drawn, unless specifically instructed to do otherwise.

  3. Note the last time the patient ate in the record and on the laboratory requisition.

  4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have the patient resume a normal diet (as prescribed).

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Monitor appropriately for hyperglycemia and hypoglycemia and provide treatment as ordered. Counsel regarding necessary lifestyle changes (e.g., diet, exercise, glycemic control, medication). Explain target blood glucose levels: before meals or upon waking, 80–120 mg/dL (4.4–6.6 mmol/L); and at bedtime, 100–140 mg/dL (5.5–7.7 mmol/L).

  3. Persons with glucose levels >200 mg/dL (>11.1 mmol/L) should be placed on a strict intake and output program.

  4. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Clinical Alert

  1. If a person with known or suspected diabetes experiences headaches, irritability, dizziness, weakness, fainting, or impaired cognition, a blood glucose test or finger stick test must be done before giving insulin. Similar symptoms may be present for both hypoglycemia and hyperglycemia. If a blood glucose level cannot be obtained and one is uncertain regarding the situation, glucose may be given in the form of orange juice, sugar-containing soda, or candy (e.g., hard candy, jelly beans). Make certain the person is sufficiently conscious to manage eating or swallowing. In the acute care setting, IV glucose may be given in the event of severe hypoglycemia. A glucose gel is also commercially available and may be rubbed on the inside of the mouth by another person if the person with diabetes is unable to swallow or to respond properly. Instruct persons prone to hypoglycemia to carry sugar-type items on their person and to wear a necklace or bracelet that identifies the person as with diabetes.

  2. Frequent blood glucose monitoring, including self-monitoring, allows better control and management of diabetes than urine glucose monitoring.

  3. When blood glucose values are >300 mg/dL (>16.6 mmol/L), urine output increases, as does the risk for dehydration.

  4. Diabetes is a “disease of the moment”: Persons living with diabetes are continually affected by fluctuations in blood glucose levels and must learn to manage and adapt their lifestyle within this framework. For some, adaptation is relatively straightforward; for others, especially those identified as being “brittle,” lifestyle changes and management are more complicated, and these patients require constant vigilance, attention, encouragement, and support.

  5. Each person with diabetes may experience certain symptoms in their own unique way and in a unique pattern.

Clinical Alert

  1. Infants with tremor, convulsion, or respiratory distress should have STAT glucose done, particularly in the presence of maternal diabetes or with hemolytic disease of the newborn.

  2. Newborns who are too small or too large for gestational age should have a glucose level measured in the first day of life.

  3. Diseases related to neonatal hypoglycemia:

    1. Glycogen storage diseases

    2. Galactosemia

    3. Hereditary fructose intolerance

    4. Ketogenic hypoglycemia of infancy

    5. Carnitine deficiency (Reye syndrome)

Interfering Factors ⬆

  1. Elevated glucose:

    1. Steroids, diuretic agents, other drugs (see Appendix E)

    2. Pregnancy (a slight blood glucose elevation normally occurs)

    3. Surgical procedures, anesthesia, and hospitalization in intensive care unit (ICU)

    4. Obesity or sedentary lifestyle

    5. Parenteral glucose administration (e.g., from total parenteral nutrition)

    6. IV glucose (recent or current)

    7. Heavy smoking

    8. The dawn phenomenon occurs in both T1D and T2D. There is an increase in blood glucose, typically between 4:00 a.m. and 8:00 a.m., due to counter-regulatory hormones, including GH, cortisol, and glucagon

  2. Decreased glucose:

    1. Hematocrit >55%

    2. Intense exercise

    3. Toxic doses of aspirin, salicylates, and acetaminophen

    4. Other drugs (see Appendix E), including ethanol, quinine, and haloperidol