A person’s A1C can be influenced by how long their red blood cells (RBC) last. A person whose RBC’s live longer will have a comparatively higher A1C, and a person whose RBC’s live shorter will have a comparatively lower A1C.
The life-span of the RBC is difficult to estimate clinically, but here is a way to estimate how long yours last compared to the average range of 100–120 days.
A reticulocyte is an immature red blood cell. They are produced in the bone marrow and released into circulation as reticulocytes, and in a few days they transform into fully mature red blood cells.
A reticulocyte count is a test that measures the level of reticulocytes in your blood.
You can use a reticulocyte count to estimate how long your red blood cells last.
A normal blood panel already gives you hematocrit (the ratio of the volume of red blood cells to the total volume of blood). So for this estimation, the only extra test you need is a reticulocyte count. (https://labtestsonline.org/tests/reticulocytes)
This is just an estimation, and blood chemistry calculations aren’t perfect. But it may give you some insight into your personal red blood cell lifespan and you can consider if it may be affecting your A1C.
Here is the formula for estimating how long your RBC’s are surviving:
RBC survival in days = 100 / (reticulocyte count (in percent) / reticulocyte life span)
You can get the reticulocyte life span from a corrected reticulocyte count table, such as shown here:
If your hematocrit is 45, the table referenced above gives a reticulocyte life span of 1.0. If your reticulocyte count is 0.7%, the formula gives:
RBC survival = 100 / (0.7 / 1.0) = 142.8 days
If your hematocrit is 28, the table referenced above gives a reticulocyte life span of 1.5. If your reticulocyte count is 1.8%, the formula gives:
RBC survival = 100 / (1.8 / 1.5) = 83.3 days
Since RBC’s are generally calculated to live 100-120 days, in example 1 the person might have an A1C that is slightly higher than what would be expected for their level of control. And in example 2, the person might have a lower A1C for their level of control.
Hope this isn’t too confusing.
(There are other ways of estimating RBC lifespan. One method involves measuring the amount of carbon monoxide in exhaled air. Another method analyzes the decay rate of Thiazole Orange stain (REticulocyte-Based-Estimation of Lifespan - REBEL), but these methods involve much more than most people would have time or ability to perform without a serious need for it. Just mentioning them for completeness.)