Eddy Edson
Well-Known Member
- Relationship to Diabetes
- Type 2
Just because I think it's interesting, this is a later study from some of the same researchers, quantifying the effect of red blood cell age on HbA1c as an estimate of avg BG: https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC5714656&blobtype=pdfThis is the foundational study from the working group which empirically established the standard best fit between blood glucose and HbA1c: https://diabetesjournals.org/care/a...nslating-the-A1C-Assay-Into-Estimated-Average
This study produced the best-fit formula which is used by BG monitors and CGM's to estimate HbA1c from BG.
The best-fit correlation is pretty good but not exact:
Even with precise, accurate, fine-grained measurements of BG, your HbA1c is unlikley to be what yr BG monitor/CGM predicts, and it's common for the variance to be as much as 20%.
It's not because of any inaccuracy in the test procedure, rather it's mainly due to the fact that the average age of red blood cells varies from person to person, generally in the range of 90 - 110 days. If two people with exactly the same BG levels have a 20% difference in their red blood cell age, then their HbA1c values will differ by 20% also.
As CGM's become more prevalent and more accurate the usefulness of HbA1c becomes less & less. It was always just a clever trick for roughly estimating avg BG levels. As it becomes more possible to measure them directly the need for the rough estimate reduces.
The glycated hemoglobin assay (HbA1c) is essential for the diagnosis and management of diabetes because it provides the best estimate of a patient’s average blood glucose (AG) over the preceding 2–3 months and is the best predictor of disease complications.
However, there is substantial unexplained glucose-independent variation in HbA1c that makes AG estimation inaccurate and limits the precision of medical care for diabetics. The true AG of a non-diabetic and a poorly-controlled diabetic may differ by less than 15 mg/dL [0.83 mmol/l], but patients with identical HbA1c and thus identical HbA1c-based estimates of AG may have true AG that differs by more than 60 mg/dl [3.3 mmol/l].
We combine a mechanistic mathematical model of hemoglobin glycation and red blood cell flux with large sets of intra-patient glucose measurements to derive patient-specific estimates of non-glycemic determinants of HbA1c including mean red blood cell age (MRBC). We find that interpatient variation in derived MRBC explains all glucose-independent variation in HbA1c.
We then use our model to personalize prospective estimates of AG and reduce errors by more than 50% in four independent sets of more than 200 patients.
The current standard of care provided AG estimates with errors > 15 mg/dL [0.83 mmol/l] for 1 in 3 patients. Our patient-specific method reduced this error rate to 1 in 10.
Turning that error rate around, it means eg that many people get a non-diabetic HbA1c measurement of say 40 mmol/l when with the same average BG level others get a "pre-diabetic" HbA1c of 46+ mmol/l and some get a full diabetic 48+ mmol/l. And so on.
Point: HbA1c really is just a rough estimate.
