Proinsulin is a hormone secreted by the pancreas. It is important to test the patient’s proinsulin level when hypoglycemia is suspected. Moreover, a patient with asymptomatic high proinsulin levels should undergo a complete evaluation. A typical proinsulin level is nine pmol/L (1.2 mU/L) while the c-peptide level is 0.26 nmol/L (0.8 mg/L).
In addition, proinsulin levels are important in determining the risk of diabetes. They are usually elevated in late-stage type 2 diabetes. Furthermore, they can help determine if a patient needs diabetes treatment. Proinsulin levels have also been associated with cardiovascular disease. In the past, it was thought that high levels of proinsulin could lead to heart disease.
Proinsulin is synthesized in the beta cells of the pancreas. Its amino acids are separated and packaged into secretory granules. Once released into the blood, it undergoes enzymatic conversion into insulin. In this process, proinsulin possesses 5% to 10% of insulin’s metabolic activity.
Proinsulin levels may be elevated in patients with insulinoma. However, their blood glucose levels are usually within normal limits. In addition, proinsulin can be a valuable biomarker for diagnosing insulinoma. The normal range for proinsulin is three to 20 pmol/l. Higher levels of proinsulin are common in Type 2 diabetes and chronic renal failure.
Proinsulin levels are a better predictor of blood glucose levels than C-peptide levels. In this study, 31 patients and 47 controls had blood glucose levels within the 2.5-3.3 mmol/l threshold. These blood glucose levels were observed after a seven-to-ten-hour fast. Proinsulin/ICL/blood glucose ratios were higher than the ROC curves, indicating a better accuracy in predicting glucose levels.