After total pancreatectomy and autologous islet transplantation, my C‑peptide is 3.3 ng/mL and random glucose is 155 mg/dL; what does this indicate about graft function and how should I manage my blood glucose?

Post-TPAIT Graft Function Assessment and Management

Interpretation of Your Results

Your C-peptide of 3.3 ng/mL with a random glucose of 155 mg/dL indicates excellent islet graft function with robust endogenous insulin production. This level of C-peptide is substantially higher than the threshold that distinguishes insulin-dependent from insulin-independent diabetes and demonstrates that your transplanted islets are actively secreting insulin 1, 2.

What These Numbers Mean

• C-peptide >0.6 ng/mL strongly indicates preserved beta cell function and argues against absolute insulin deficiency 1, 2
• Your level of 3.3 ng/mL is approximately 5-fold higher than the diagnostic threshold, suggesting substantial islet mass has engrafted successfully 1, 3
• The random glucose of 155 mg/dL in the context of this robust C-peptide indicates relative insulin resistance rather than inadequate insulin production 1
• Even partial graft function (which you clearly exceed) provides >90% reduction in severe hypoglycemia incidence through restoration of endogenous glucose counter-regulation 4

Primary Clinical Implications

The primary goal after TPAIT is elimination of severe hypoglycemia, which your C-peptide level strongly predicts you will achieve 4. Clinical trial data show that 82% of islet transplant recipients achieve HbA1c <7.0% with elimination of severe hypoglycemia at 1 year, and 70% maintain this at 2 years 4.

Graft Function Status

• Your graft is functioning robustly – C-peptide levels >0.6 ng/mL are associated with better A1C, lower risk of retinopathy, lower risk of nephropathy, and lower risk of severe hypoglycemia 5, 6
• The mechanism of protection is restoration of endogenous glucose production in response to insulin-induced hypoglycemia, which protects against problematic hypoglycemia even if you still require some exogenous insulin 4

Blood Glucose Management Strategy

Insulin-Sensitizing Approach

Given your high C-peptide, your management should focus on insulin sensitization rather than insulin replacement 1:

• Start metformin as first-line therapy to address the insulin resistance component 1
• Implement intensive lifestyle modification including nutrition counseling aimed at weight optimization 1
• Target at least 60 minutes daily of moderate-to-vigorous exercise to enhance insulin sensitivity 1
• Consider thiazolidinediones if metformin alone is insufficient, as they enhance cellular responsiveness to insulin and improve hepatic insulin sensitivity 1

Monitoring Protocol

• Monitor HbA1c every 3 months and intensify treatment if not meeting goals 1
• Target HbA1c <7.0% to reduce microvascular disease risk 1, 4
• Use finger-stick glucose monitoring when initiating or changing treatment regimens 1

Critical Caveats

Do not measure C-peptide within 2 weeks of any hyperglycemic emergency, as results will be unreliable 1, 6. Your current measurement appears valid given the context provided.

Standard insulin therapy does not increase endogenous C-peptide production – it replaces insulin but does not restore additional beta cell function 6. Your current C-peptide reflects the transplanted islet mass that successfully engrafted.

The presence of measurable C-peptide does not predict better response to insulin therapy if insulin is clinically indicated; treatment decisions should be based on glycemic control, not C-peptide levels alone 1, 6.

Insulin Therapy Considerations

You may require minimal or no exogenous insulin given your robust C-peptide level 1, 3. If you are currently on insulin:

• After achieving improved glycemic control with insulin-sensitizing agents, it may be possible to reduce or discontinue insulin if lifestyle modification and oral agents maintain target glucose levels 1
• A C-peptide level approaching ≤0.6 ng/mL in the future would indicate progressive loss of graft function and signal a shift toward absolute insulin deficiency 1

Long-Term Outlook

Your excellent graft function positions you to achieve the primary benefit of islet transplantation: elimination of severe hypoglycemia 4. Continue lifelong immunosuppression as prescribed to prevent graft rejection, and monitor kidney function regularly as accelerated decline is the most significant adverse outcome of immunosuppression 4.