How Helpful Are Laboratory Tests?
In patients with T2DM, both plasma insulin and C peptide concentrations are usually high, reflecting underlying insulin resistance.14 Chronic hyperglycemia, however, can cause transient insulin deficiency with a low initial plasma insulin concentration despite insulin resistance. Insulin and C peptide levels therefore may be deceptively low in the presence of acute metabolic deterioration at the time of presentation. Conversely, “insulin reserve” can persist in patients with T1DM for up to two years. Thus, although measurement of insulin and C peptide can be helpful in making the distinction between T1DM and T2DM — particularly when levels are elevated — a significant degree of overlap exists.
