Cleveland Clinic Journal of Medicine
https://pubmed.ncbi.nlm.nih.gov/?myncbishare=dukemlib&dr=abstract&otool=dukemlib&term=33526460
There are a LOT of conditions that can affect hemA1c such as chronic kidney or liver disease, hemolytic anemia, iron deficiency, pregnancy, as well as b12 and folate deficiencies. There are several ways around this including more frequent glucose monitoring, serum fructosamine, and there is work now looking at the value of glycated albumin.