Hi and welcome to the forum
@Shellrich . I’m sorry to hear that your husband is going through all this.
As you probably know C-Peptides are produced by the pancreas and are a by product of insulin production. C-Peptides are proportional to insulin. They are measured in preference to insulin because they are more stable. Low C-Peptides are one of the main indicators of Type 1 diabetes, along with the presence of autoantibodies. T1 is an autoimmune condition whereby the body attacks and kills the insulin producing beta cells. Once these cells are destroyed they are gone, but in the early days of adult onset T1 or LADA beta cells can continue to replicate and produce some insulin, albeit deteriorating over time. This deterioration can happen in fits and starts. Two different c peptides readings would not be unusual as late onset T1 is not as destructive as child onset T1, meaning it can take much longer for the beta cell mass to be totally destroyed and not produce any insulin at all in late adult onset. They will very likely test him for autoimmune antibodies. If present, will confirm T1. As his C-Peptides are fluctuating but very low, he will likely be producing some of these autoantibodies. There are 4 types , GAD antibodies are the most common of the 4, but not exclusively so. Of course, if he stops producing any insulin at all, due to the total destruction of beta cells, then autoantibodies will likely not be present, but no insulin production would also lead to a diagnosis of T1. I hope that makes sense.