MONITORING GLUCOSE LEVELS AND KETONES
Blood glucose monitoring is a cornerstone of diabetes manage-ment, and self-monitoring of blood glucose (SMBG) levels by patients has dramatically altered diabetes care. Frequent SMBG enables people with diabetes to adjust the treatment regimen to obtain optimal blood glucose control. This allows for detection and prevention of hypoglycemia and hyperglycemia and plays a crucial role in normalizing blood glucose levels, which in turn may reduce the risk of long-term diabetic complications.
Various SMBG methods are available. Most involve obtain-ing a drop of blood from the fingertip, applying the blood to a special reagent strip, and allowing the blood to stay on the strip for the amount of time specified by the manufacturer (usually 5 to 30 seconds). The meter gives a digital readout of the blood glucose value.
The meters available for SMBG offer different features and benefits. Newer monitors have eliminated the step of blood re-moval from the strip. The strip is placed in the meter first, before blood is applied to it. Once the blood is placed on the strip, it remains there for the duration of the test. The meter automati-cally displays the blood glucose level after a short time (less than 1 minute). Some meters are biosensors that use blood obtained from alternate test sites, such as the forearm. They have a special lancing device that is useful for patients who have painful finger-tips or pain with finger sticks.
Some meters can be used by patients with visual impairments. They have audio components that assist the patient in perform-ing the test and obtaining the result. In addition, meters are avail-able to check both blood glucose and blood ketone levels by those who are particularly susceptible to development of DKA.
The monitoring method used by the patient must match his or her skill level. Factors affecting SMBG performance include visual acuity, fine motor coordination, cognitive ability, comfort with technology, willingness, and cost.
Visual methods are the least expensive and require less equip-ment. However, they require the ability to distinguish colors and to be exact in timing the procedures. Further, they involve sub-jective interpretation of results. Monitoring blood glucose using meters is recommended because meters have become much less expensive and less technique-dependent, making the results more accurate. Referral to a social worker may be warranted to assist in-dividuals without the financial means to purchase a meter.
Older meters that required removal of blood from the reagent strip are generally obsolete. These procedures have more steps that must be performed in an exact sequence. The newer meters that do not require removal of blood from the strip generally are easier to use. However, most do not provide a backup method for visually assessing the meter results. Figure 41-3 illustrates a system for glucose monitoring.
A potential hazard of all SMBG methods is that the patient may obtain and report erroneous blood glucose values as a result of using incorrect techniques. Some common sources of error include:
• Improper application of blood (eg, drop too small)
• Improper meter cleaning and maintenance (eg, allowing dust or blood to accumulate on the optic window). This is not an issue in the biosensor type of meter.
• Damage to the reagent strips by heat or humidity; use of outdated strips
The nurse plays an important role in providing initial teach-ing about SMBG techniques. Equally important is evaluating the techniques of patients who are experienced in self-monitoring. Patients should be discouraged from purchasing SMBG products from stores or catalogs that do not provide direct education. Every 6 to 12 months, patients should conduct a comparison of their meter with a simultaneous laboratory-measured blood glu-cose level in their physician’s office. The accuracy of the meter and strips should also be assessed with control solutions specific to that meter whenever a new vial of strips is used or whenever the validity of the reading is in doubt.
For everyone with diabetes, SMBG is useful for managing self-care. It is a key component of treatment for any intensive insulin therapy regimen (including two to four injections per day or in-sulin pumps) and for diabetes management during pregnancy. It is also recommended for patients with:
• Unstable diabetes
• A tendency for severe ketosis or hypoglycemia
• Hypoglycemia without warning symptoms
For patients not taking insulin, SMBG is helpful for moni-toring the effectiveness of exercise, diet, and oral antidiabetic agents. It can also help motivate patients to continue with treat-ment. For patients with type 2 diabetes, SMBG is recommended during periods of suspected hyperglycemia (eg, illness) or hypo-glycemia (eg, unusual increased activity levels) (ADA, Physical Activity/Exercise and Diabetes Mellitus, 2003).
For most patients who require insulin, SMBG is recommended two to four times daily (usually before meals and at bedtime). For patients who take insulin before each meal, SMBG is required at least three times daily before meals to determine each dose (ADA, Tests of Glycemia in Diabetes, 2002). Patients not receiving in-sulin may be instructed to assess their blood glucose levels at least two or three times per week, including a 2-hour postprandial test. For all patients, testing is recommended whenever hypoglycemia or hyperglycemia is suspected. The patient should increase the frequency of SMBG with changes in medications, activity, or diet and with stress or illness.
Patients are instructed to keep a record or logbook of blood glu-cose levels so that they can detect patterns. Testing is done at the peak action time of the medication to evaluate the need for dosage adjustments. To evaluate basal insulin and determine bolus insulin doses, testing is performed before meals. To titrate bolus insulin doses, regular or lispro, testing is done 2 hours after meals. Patients with type 2 diabetes are encouraged to test before and 2 hours after the largest meal of the day. Patients who take insulin at bedtime or who are on an insulin infusion pump must also test at 3 a.m. once a week to document that the blood glucose level is not decreasing during the night. If a patient is unwilling or can-not afford to test frequently, then once or twice a day may be suf-ficient if the patient varies the time of day to test (eg, before breakfast one day, before lunch the next day).
A tendency to discontinue SMBG is more likely to occur when patients do not receive instruction about using the results to alter their treatment regimen. Instructions vary according to the patient’s understanding and the physician’s philosophy of dia-betes management. At the very least, patients should be given parameters for calling the physician. Patients using intensive in-sulin therapy regimens may be instructed in the use of algorithms (rules or decision trees) for changing the insulin doses based on patterns of values greater or less than the target range and the amount of carbohydrate to be consumed. Baseline patterns should be established by SMBG for 1 to 2 weeks.
Glycosylated hemoglobin (referred to as HgbA1Cor A1C) is ablood test that reflects average blood glucose levels over a period of approximately 2 to 3 months (ADA, Tests of Glycemia in Diabetes, 2003). When blood glucose levels are elevated, glucose molecules attach to hemoglobin in the red blood cell. The longer the amount of glucose in the blood remains above normal, the more glucose binds to the red blood cell and the higher the gly-cosylated hemoglobin level. This complex (the hemoglobin at-tached to the glucose) is permanent and lasts for the life of the red blood cell, approximately 120 days. If near-normal blood glucose levels are maintained, with only occasional increases in blood glu-cose, the overall value will not be greatly elevated. However, if the blood glucose values are consistently high, then the test result will also be elevated. If patients report mostly normal SMBG results but the glycosylated hemoglobin is high, there may be errors in the methods used for glucose monitoring, errors in recording re-sults, or frequent elevations in glucose levels at times during the day when the patient is not usually monitoring the blood.
Various tests measure the same thing but have different names, including hemoglobin A1C and hemoglobin A1. The normal val-ues differ slightly from test to test and from laboratory to labo-ratory and normally range from 4% to 6%. Values within the normal range indicate consistently near-normal blood glucose levels, a goal made easier by SMBG.
Before SMBG methods were available, urine glucose testing was the only way to monitor diabetes on a daily basis. Today its use is limited to patients who cannot or will not perform SMBG. The advantages of urine glucose testing are that it is less expensive than SMBG and it is not invasive. The general procedure involves ap-plying urine to a reagent strip or tablet and matching colors on the strip with a color chart at the end of a specified period.
Disadvantages of urine testing include the following:
• Results do not accurately reflect the blood glucose level at the time of the test.
• The renal threshold for glucose is 180 to 200 mg/dL (9.9 to 11.1 mmol/L), far above target blood glucose levels.
• Hypoglycemia cannot be detected because a “negative” urine glucose result may occur when the blood glucose level ranges from 0 to 180 mg/dL (9.9 mmol/L) or higher.
• Patients may have a false sense of being in good control when results are always negative.
• Various medications (eg, aspirin, vitamin C, some anti-biotics) may interfere with test results.
• In elderly patients and patients with kidney disease, the renal threshold (the level of blood glucose at which glucose starts to appear in the urine) is raised; thus, false-negative readings may occur at dangerously elevated glucose levels.
Ketones (or ketone bodies) in the urine signal that control of type 1 diabetes is deteriorating, and the risk of DKA is high. When there is almost no effective insulin available, the body starts to break down stored fat for energy. Ketone bodies are byproducts of this fat breakdown, and they accumulate in the blood and urine. Urine testing is the most common method used for self-testing of ketone bodies by patients. A meter that enables testing of blood for ketones is available but not widely used.
Most commonly, patients use a urine dipstick (Ketostix or Chemstrip uK) to detect ketonuria. The reagent pad on the strip turns purplish when ketones are present. (One of the ketone bodies is called acetone, and this term is frequently used inter-changeably with the term “ketones.”) Other strips are available for measuring both urine glucose and ketones (Keto-Diastix or Chemstrip uGK). Large amounts of ketones may depress the color response of the glucose test area.
Urine ketone testing should be performed whenever patients with type 1 diabetes have glucosuria or persistently elevated blood glucose levels (more than 240 mg/dL or 13.2 mmol/L for two testing periods in a row) and during illness, in pregnancy with pre-existing diabetes, and in gestational diabetes (ADA, Tests of Glycemia in Diabetes, 2003).