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Methods of Monitoring Glycemic Control

SMBG

This involves checking Capillary Blood Glucose at set times of the day. A log is kept and brought to appointments to assist in managent of diabetes therapy. In patients with MDI (multiple daily injection) regimen, there are four primary times to check:

  1. Fasting Blood Glucose (FBG). This is usually before breakfast
  2. Pre-Lunch
  3. Pre-Dinner
  4. Bedtime

These checks help to inform adjustments of basal and prandial insulin (Figure 3).

  1. FBG informs basal insulin adjustment
  2. Pre Lunch informs breakfast prandial insulin adjustment
  3. Pre Dinner informs lunch prandial insulin adjustment
  4. Bedtime informs dinner prandial insulin adjustment

For example, if BG increases significantly between pre lunch and pre dinner checks, lunch prandial insulin may need to be adjusted

Figure 1. SMBG
Figure 1. SMBG

If pre-prandial checks are at goal, but A1c is still elevated, guidelines recommend post-prandial checks as post-prandial excursions may be responsible for persistently elevated A1c despite goal pre-prandial checks.

A1c

Hemoglobin A1c gives a 3 month estimate of glycemic control and is correlated to estimated Average Glucose (eAG) which can be derived by the A1c via the following calculator:

A1c Table

Continuous Glucose Monitor (CGM)

CGM technology records interstial blood glucose continuously throughout the day at set intervals (typically 5 minute intervals) and gives information about both glucose values and trends.

Why do these measures of glycemic control matter?

Each of these measures of glycemic control have been found to be associated with risk of microvascular complications of diabetes as is demonstrated in the following pages.

SMBG and A1C

DCCT

https://www.ncbi.nlm.nih.gov/pubmed?term=8366922

Intensive vs conventional groups

Figure 2. Measurements of A1c and Capillary blood glucose in patients with IDDM receiving intensive or conventional therpy.
Figure 2. Measurements of A1c and Capillary blood glucose in patients with IDDM receiving intensive or conventional therpy.

Microvascular Complications between groups

Retinopathy

Cumulative incidence of sustained change in retinopathy (change observed by fundus photography of at least three steps form basline, sustained for at least six months)

Figure 3: primary prevention cohort–intensive therapy reduced adjusted mean risk of onset of retinopathy by 76% during course of study.
Figure 3: primary prevention cohort–intensive therapy reduced adjusted mean risk of onset of retinopathy by 76% during course of study.
Figure 4: intensive therapy reduced adjusted mean risk of progression of retinopathy by 54% as compared with conventional therapy.
Figure 4: intensive therapy reduced adjusted mean risk of progression of retinopathy by 54% as compared with conventional therapy.

Nephropathy

Urinary Albumin Excretion >/= 300mg/24hrs (dashed line), >/=40mg per 24hrs (solid line) in patients with IDDM Receiveing Intensive or Conventional Therapy

Figure 5: primary prevention cohort–intensive therapy reduced the adjusted mean risk of microalbuminuria by 34%.
Figure 5: primary prevention cohort–intensive therapy reduced the adjusted mean risk of microalbuminuria by 34%.
Figure 6: Secondary intervention cohort–intensive therapy reduced adjusted mean risk of albuminuria by 56% and the risk of microalbuminuria by 43%
Figure 6: Secondary intervention cohort–intensive therapy reduced adjusted mean risk of albuminuria by 56% and the risk of microalbuminuria by 43%

Neuropathy

Figure 7:Prevalance of abnormal clinical neurologic examinations, abnormal nerve conduction studies, abnormal autonomic nerve studies at five years in patients receiving intensive(solid bars) or conventional (Hatched bars) therapy.
Figure 7:Prevalance of abnormal clinical neurologic examinations, abnormal nerve conduction studies, abnormal autonomic nerve studies at five years in patients receiving intensive(solid bars) or conventional (Hatched bars) therapy.

CGM

Validation of Time in Range as an outcome Measure for Diabetes Clinical Trials

https://care.diabetesjournals.org/content/42/3/400

Figure 8: Frequency of development of microvascular complication according to level of TIR (70–180 mg/dL) computed from quarterly seven-point blood glucose testing.
Figure 8: Frequency of development of microvascular complication according to level of TIR (70–180 mg/dL) computed from quarterly seven-point blood glucose testing.

CGM vs A1c

The following example provides two separate scenarios of glucose trends which both equate to the same A1c (7%)

As can be seen, A1c does not give good information about hypoglycemia or hyperglycemia if there are large glycemic excursions. In scenario 1, the periods of hypoglycemia are balanced by the periods of hyperglycemia to equate to the same A1c as scenario 2. This additional information is very useful in adjusting therapy and for safety, as hypoglycemia is directly related to cardiac arrhythmias.

Glycemic goals

There are several different guidelines for glycemic goals for DM. Newer guidelines emphasize individualizing glycemic targets based on individual patient characteristics. The following is a summary of ADA guidelines for DM based on health status and age category:

For more information and definitions, see ADA guidelines:

Proposed CGM goals:

Where TIR=Time in Range, TAR=Time Above Range, TBR=Time Below Range
These ranges are readily available from CGMs, and can be less accurately (due to much less data) estimated from SMBG data or glucometers. The following site can assist with estimating ranges and graphing trends from SMBG data uploaded in excel format:
https://insulin.ddns.net/dm/log/

Case 2