Norm of Glucose Monitoring Machines
Whole-blood glucose values are about 15% less than serum glucose values as a result of greater dilution.
|Newborn to 24 hours
|Newborn >24 hours
Usage of Glucose Monitoring Machines
Chronic glucose monitoring for diabetes mellitus, monitoring for hypoglycemia in newborn, and bedside whole-blood glucose analysis.
Description of Glucose Monitoring Machines
Blood glucose monitoring is generally considered to be more reliable for diabetic glucose monitoring than urine glucose levels. This is particularly true for clients with an abnormally low renal threshold for glucose reabsorption after glomerular filtration. The term “glucose monitoring machines” encompasses a variety of reflectance meters (including voice-activated machines) that can be used to quickly quantitate whole-blood glucose levels. In general, the technique involves applying a drop of capillary or venous blood to a reagent strip, blotting the drop after a specific time period, inserting the strip into the reflectance meter, and then following the manufacturer's recommended steps for processing. The result is generally obtained within 2 to 3 minutes and has been estimated to cost as little as one twentieth of a “stat.” laboratory glucose measurement. Home meters need to be verified at regular intervals, as one third of readings deviated significantly in one study (Henry et al, 2001).
Professional Considerations of Glucose Monitoring Machines
Consent form NOT required.
- Verify that the client's hematocrit level is within the range for which the specific brand of machine is designed to be accurate. If the hematocrit is outside the required range, perform the glucose blood test instead of this test.
- Verify that the machine has been calibrated within the time requirements specified by the manufacturer.
- Obtain an alcohol wipe, a 2.5-mm lancet (or a needle and a syringe), a reagent strip, a cotton ball, a reflectance meter, sterile gauze, and a capillary tube if heelstick blood will be used.
- Read the instructions for the specific reflectance meter to be used.
- Fingerstick capillary method:
- a. Cleanse the lateral aspect of the pad of the finger with an alcohol wipe and allow the area to dry.
- b. Using a 2.5-mm lancet, puncture the lateral aspect of the pad of the finger. Wipe the first drop of blood away with sterile gauze.
- c. Holding the puncture site dependent, allow a second, large drop of blood to accumulate and drop onto the reagent strip, making sure there is enough blood to completely cover the pad of the reagent strip. The pad of the finger may be very gently and repeatedly pressed to encourage blood flow, but avoid milking the finger.
- d. Follow directions for the specific reflectance meter being used.
- Heelstick capillary method:
- a. Prewarming the heel is not necessary.
- b. Avoid puncturing over previous puncture sites or puncturing the posterior curvature of the heel.
- c. Cleanse an area on the medial or lateral plantar surface of the heel with 70% alcohol and allow the area to dry.
- d. Using a 2.5-mm lancet, puncture the heel until a free flow of blood is obtained. Wipe the first drop of blood away with sterile gauze.
- e. Holding the puncture site dependent, allow a second, large drop of blood to accumulate and drop onto the reagent strip, making sure that there is enough blood to completely cover the pad of the reagent strip. Avoid milking the heel.
- f. Follow the directions for the specific reflectance meter being used.
- Venous method:
- a. Obtain a 4-mL venous blood sample in a syringe or green-topped tube.
- b. Completely cover the pad of the reagent strip with a drop of the blood specimen.
- c. Follow the directions for the specific reflectance meter being used.
- Hold pressure to the site until the bleeding stops. Leave puncture sites open to the air to heal.
Client and Family Teaching
- Teach the newly diagnosed client with diabetes how to perform a fingerstick and use a reflectance meter.
- Watch for signs of hyperglycemia and hypoglycemia (see Glucose—Blood for symptoms and treatment).
- Bring a home reflectance meter to office appointments with the physician so that technique and machine calibration may be assessed.
Factors That Affect Results
- After the skin is cleansed with alcohol, the skin must be allowed to dry completely before the puncture is performed.
- Failure to completely cover the reagent area with blood may cause inaccurate results.
- Using too little or too much blood may cause inaccurate results. Cotton, rather than gauze, should be used for blotting the strip.
- Failure to follow timing instructions exactly as recommended by the manufacturer may cause inaccurate results.
- The most accurate and reliable results are obtained when the reflectance meter is calibrated according to the schedule recommended by the manufacturer.
- Instruments used for monitoring of hypoglycemia in newborns must have the calibration adjusted for this purpose.
- For glucose levels >400 mL/dL, accuracy of Chemstrip bG and the Accu-Chek reflectance meter has been shown to improve when a 4-mL specimen of heparinized blood is diluted with 2 mL of 0.9% saline and the corresponding result is multiplied by 3 to correct for dilution.
- Vigorous milking of the heel or finger may cause falsely low results because of dilution of the specimen with interstitial fluid.
- Many conditions and drugs affect glucose levels (see Glucose—Blood ).
- In normal clients, blood glucose levels return to fasting levels within 2 hours postprandially.
- Glucose monitoring machine: competency of the operator may be evaluated by assessment of results of control solutions.
- Incidence of significant error ranges from 6% to 76%.