HbA1c Testing: Impact of Blood Donation and Accuracy Concerns

Q: HbA1c Testing: Impact of Blood Donation and Accuracy Concerns

Dear Mr. Xiao Lu： 1. The diagnosis of diabetes has consensus standards in medicine： According to the diagnostic criteria from the American Diabetes Association, a. Fasting plasma glucose level ≥126 mg/dL after at least 8 hours of fasting, b. 2-hour plasma gluco

Glycated Hemoglobin Test (HbA1c Test)

Hello Doctor: Recently, I have been experiencing intermittent itching around the skin near my ankles.
I found online that this could be a symptom of peripheral neuropathy related to diabetes.
Two years ago, my company's health check report showed a hemoglobin A1c level of 5.8 (the A1c test was removed from last year's health check).
I am now a bit concerned and plan to get a blood test at the laboratory.
I would like to ask you, if I donated 500cc of blood last month, will this affect the results of the hemoglobin A1c test? Additionally, is the margin of error for commercially available hemoglobin A1c testing devices larger than that of hospital testing methods?

Xiao Lu, 30~39 year old female. Ask Date: 2017/10/14

Dr. Xiao Yongxun reply Internal Medicine

Dear Mr.
Xiao Lu:
1.
The diagnosis of diabetes has consensus standards in medicine: According to the diagnostic criteria from the American Diabetes Association, a.
Fasting plasma glucose level ≥126 mg/dL after at least 8 hours of fasting, b.
2-hour plasma glucose level ≥200 mg/dL during an oral glucose tolerance test, c.
HbA1c ≥6.5% (must not have any disproportionate hyperglycemia and the testing method must comply with the international certification standards of NGSP and DCCT).
Any of the above a, b, or c must be confirmed on two separate occasions.
d.
Clinical symptoms of diabetes (such as polydipsia, polyuria, polyphagia, weight loss, etc.) with any plasma glucose level ≥200 mg/dL (this condition only requires one occurrence).
2.
Your HbA1c is 5.8%, which does not meet the diagnostic criteria.
On the other hand, although HbA1c was not tested, you can refer to your fasting blood glucose level.
Generally, a normal fasting plasma glucose level is less than 100 mg/dL.
If it is between 100 mg/dL and 126 mg/dL, it can be considered as prediabetes or impaired fasting glucose.
Of course, if postprandial blood glucose is greater than or equal to 126 mg/dL, diabetes should be suspected.
3.
Theoretically, unless a large volume of blood donation leads to anemia, the impact on HbA1c levels should be minimal.
4.
Regarding the "commercially available HbA1c testing device" you mentioned: to my knowledge, since laboratory measurements of HbA1c must comply with the international certification standards of NGSP and DCCT, it may refer to a blood glucose meter.
For domestically produced blood glucose meters, both reliability and validity should be good, with minimal differences.
However, blood glucose meters measure capillary blood glucose levels, while laboratories check plasma glucose levels.
The diagnosis of diabetes is primarily based on plasma glucose levels.
The former can sometimes differ by about 10-20 mg/dL, usually on the lower side.
5.
If you have further questions, I recommend discussing them thoroughly with your family physician; there is no need for excessive panic.
[Note] I apologize for the delayed response due to personal operating system issues.

Reply Date: 2017/10/14

More Info

When interpreting HbA1c (glycated hemoglobin) testing results, it's essential to understand how various factors, including blood donation, can influence the accuracy of the results. HbA1c is a critical marker for assessing long-term glucose control in individuals, particularly for diagnosing and monitoring diabetes.
Firstly, regarding your concern about the potential impact of donating blood on your HbA1c levels, it is important to note that donating 500cc of blood typically does not have a significant effect on your HbA1c results. HbA1c reflects the average blood glucose levels over the past two to three months, as it measures the percentage of glucose that has attached to hemoglobin in red blood cells. Since red blood cells have a lifespan of about 120 days, the donation of blood would not drastically alter the overall percentage of glycated hemoglobin in your system immediately after the donation. However, if you are concerned about your blood glucose levels, it is advisable to wait a few weeks after donating blood before having your HbA1c tested to ensure that your body has had adequate time to replenish its red blood cells.

As for the accuracy of home HbA1c testing devices compared to laboratory testing, there can indeed be variability. Laboratory tests are typically more accurate and are conducted under controlled conditions by trained professionals. They utilize standardized methods that are validated for precision. On the other hand, home testing devices may have a wider margin of error due to factors such as user technique, device calibration, and the specific technology used in the device. Therefore, while home testing can provide a quick estimate of your HbA1c levels, it is always best to confirm any concerning results with a laboratory test.

In your case, given the symptoms you mentioned—itching around the ankles, which could be related to peripheral neuropathy often associated with diabetes—it's prudent to have a comprehensive evaluation. Symptoms like these warrant further investigation, especially if you have a family history of diabetes or other risk factors.
Additionally, if your previous HbA1c was 5.8%, it indicates that you were within the normal range, but it's essential to monitor any changes, especially if you are experiencing new symptoms. If your upcoming tests show an increase in HbA1c levels, it may suggest a trend towards impaired glucose metabolism, and you should discuss this with your healthcare provider for appropriate management strategies.

In summary, while donating blood does not significantly impact HbA1c results, it is wise to allow some time before testing. Laboratory tests are generally more reliable than home testing devices. Given your symptoms and previous HbA1c levels, it would be beneficial to follow up with your healthcare provider for a thorough assessment and to discuss any necessary lifestyle modifications or treatments to manage your health effectively. Regular monitoring and proactive management are key in preventing the progression of diabetes and its complications.

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