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How long do you need to wait to see a change
in hemoglobin A1C after making a modification in a diabetes medication
regimen or lifestyle change?
1. 7 Days
2. 14 Days
3. 30 Days
4. 60 Days
5. 90 Days
Response
The MNCD does make specific mention that testing as frequently as monthly
may be appropriate in pregnant women, and that testing every 1-2 months
(with appropriate documentation) may be appropriate in patients with
uncontrolled diabetes undergoing treatment changes.
Because A1C seems to have a half-life of about 28 days, of the eventual
change in A1C that would occur over 3 months after a change in treatment,
perhaps 50% will occur within 1 month and 75% in 2 months. Therefore
to see if you are making the correct changes to your patient’s
therapy, you could consider testing the A1c within 30 days to see that
your changes are effective. You will see a change over 30 days if it
is meaningful.
The glycosylated hemoglobin (A1C) concentration reflects the time-weighted
average of mean daily plasma glucose over 2-3 months.[1,2] Thus, it
is generally appropriate to wait 3 months to see the full effect of
a change in treatment on A1C. However, if the change in treatment involves
the addition or change in dose of a thiazolidinedione, it may take 2-3
months more to see the full effect on fasting glucose. Thus, one might
expect that it would take 4-6 months or more to see the full effect
on A1C.
A practical issue is that the Medicare National Coverage Determination
(MNCD)[3] suggests that the 3-month interval may be necessary to monitor
patients with diabetes whose control has been, on average, within the
target range. If substantial changes in mean glucose have occurred,
one can repeat the measurement more often if there is a need to estimate
the proportion and magnitude of the change in average glycemia. Because
A1C seems to have a half-life of about 28 days, of the eventual change
in A1C that would occur over 3 months after a change in treatment, perhaps
50% will occur within 1 month and 75% in 2 months. The MNCD does make
specific mention that testing as frequently as monthly may be appropriate
in pregnant women, and that testing every 1-2 months (with appropriate
documentation) may be appropriate in patients with uncontrolled diabetes
undergoing treatment changes.
References
1. Cefalu WT, Wang ZQ, Bell-Farrow A, Kiger FD, Izlar C. Glycohemoglobin
measured by automated affinity HPLC correlates with both short-term
and long-term antecedent glycemia. Clin Chem. 1994;40:1317-1321. Abstract
2. Allgrove J, Cockrill BL. Fructosamine or glycated haemoglobin as
a measure of diabetic control? Arch Dis Child. 1988;63:418-422. Abstract
3. Centers for Medicare & Medicaid Services. National Coverage Determinations:
Glycated Hemoglobin/Glycated Protein. Available at: http://www.cms.hhs.gov/ncd/searchdisplay.asp?NCD_ID=100&NCD_vrsn_num=1
Accessed September 1, 2003.
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