How to Use a Capillary Blood Glucose (CBG) Monitor
All patients with diabetes using their own blood glucose monitor must be instructed in the correct technique for sample collection, meter operation, and quality control procedures. 1
Essential Training Components
Initial Setup and Quality Control
- Verify meter accuracy standards: Only use FDA-approved meters with proven accuracy that meet current regulatory standards 1
- Use only unopened, unexpired test strips purchased from licensed pharmacies or distributors, as preowned or secondhand strips may give incorrect results 1
- Store strips properly according to manufacturer instructions to maintain accuracy 1
- Perform quality control checks as recommended by the device manufacturer 1
Proper Testing Technique (13-Point Critical Steps)
The following technique elements are essential for accurate readings 2:
- Wash hands thoroughly with soap and warm water before testing, or use an alcohol wipe and allow to dry completely 3, 4
- Check meter calibration and ensure it matches the test strip batch code (if required by your specific meter) 2
- Use the side of the fingertip rather than the pad, as this area is less sensitive and has adequate blood flow 3
- Obtain an adequate blood sample size as specified by your meter (insufficient sample is a common error) 2
- Apply blood to the test strip correctly according to manufacturer instructions—some require a hanging drop, others allow touching the strip to blood 3
- Wait for the full testing cycle to complete before reading results 2
- Record results immediately with date, time, and any relevant context (meals, exercise, symptoms) 4
When to Test
For Patients on Intensive Insulin Therapy (Multiple Daily Injections or Pump)
Test 6-10 times daily at the following times 5, 6:
- Before each meal and snack
- At bedtime
- Occasionally 2 hours after meals
- Before, during, and after exercise
- When hypoglycemia is suspected
- After treating low blood glucose until normalized
- Before and during critical tasks such as driving
For Patients on Basal Insulin Only
Prioritize fasting blood glucose measurement as this directly informs dose adjustment of long-acting insulin 5, 6
For Patients on Oral Agents Alone
Routine monitoring is NOT recommended once treatment goals are met, as evidence shows limited clinical benefit 1
Critical Safety Considerations
When CBG May Be Inaccurate
You MUST have access to CBG testing even if using continuous glucose monitoring (CGM) for the following situations 1:
- Whenever you suspect the CGM is inaccurate
- During CGM sensor warm-up periods
- For CGM calibration (if required by your device)
- When glucose levels are changing rapidly (>2 mg/dL/min)
- If a CGM warning message appears
Interfering Substances
Be aware that certain medications can affect glucose readings 1:
- Glucose oxidase meters can be affected by: uric acid, galactose, xylose, acetaminophen, L-dopa, and ascorbic acid
- Glucose dehydrogenase meters can be affected by: icodextrin (used in peritoneal dialysis)
Common Pitfalls to Avoid
- Don't assume your meter is accurate just because it's FDA-cleared—substantial variation exists in accuracy among widely used systems, with only 6 of the top 18 meters meeting accuracy standards in one analysis 1
- Don't test during periods of rapid glucose change if possible, as this reduces accuracy 5
- Don't ignore technical errors—even multiple technical errors can still yield clinically useful values in most cases, but dangerously inaccurate readings do occur 2
Using the Data Effectively
Testing without action is futile. You must be educated on how to use CBG data to adjust food intake, physical activity, or medications to achieve specific glycemic goals 1, 6. Each additional CBG check per day is associated with a 0.2% reduction in HbA1c when results are acted upon 6.
Structured review of glucose patterns with your healthcare provider improves HbA1c by an additional 0.3 percentage points compared to unstructured monitoring 5.
Technique Verification
Have your testing technique observed and verified by your healthcare provider or diabetes educator initially and at regular intervals, as accuracy is both instrument and user dependent 5, 2.