Starting Insulin Rates in Pump Users

A preliminary retrospective study that compared four different methods of estimating starting basal insulin infusion rates when transitioning to pump therapy has found that the currently recommended total daily insulin dose method is the safest and most accurate approach in type 1 diabetes (T1DM) patients. The study also found that a newly developed “regression formula” for determining starting basal insulin rates may be the most accurate approach in patients with T2DM. Results were published online in BMJ Open Diabetes Research Care.

“With preliminary evidence suggesting there is room for improvement over pre-existing estimates, further development of these regression formulas may yield a new clinical tool for [insulin infusion therapy] initiation in both patients with type 1 and 2 diabetes. Better calibrated estimate methods may be safer and require less intervention during the time of pump initialization, improving patient satisfaction and overall treatment efficiency for this period,” wrote lead author Hugh D. Tildesley, MD, of St. Paul’s Hospital (Vancouver, British Columbia, Canada), and colleagues. 

Transitioning to pump therapy can be challenging, especially due to the increased risk of hypoglycemia during this period. Scientific and industry consensus currently agrees that both weight-based and total daily dose of insulin methods can be used in patients with T1DM to determine starting basal rates of insulin infusion when transitioning to pump therapy. However, no widely recommended method for estimating starting basal rates exists in patients with T2DM. Which methods are safest and most effective has been an open question both for patients with T1DM and T2DM.   

In the study, researchers evaluated medical records of patients with T1DM (n=61) and T2DM (n=34) who were on insulin pump therapy for at least three months, and had been seen at a private diabetes clinic in Canada. They calculated starting basal rates retrospectively using weight-based and total daily dose of insulin methods. Then they compared these established methods to an empirically derived value of 0.8 U/h, which observational data had shown to be the starting basal rate for many patients. Finally, they compared these methods to a fourth method that they developed using statistical regression techniques (e.g. “regression formula”).

Key Results:

• T1DM:

♦ Significant, positive correlation between weight and total daily insulin dose methods and final basal rates (P<0.01 and P<0.001, respectively)

♦ Accuracy: Regression formula was most accurate (median absolute percentage error 11.9%), followed by the total daily insulin dose method (17.5%), the weight-based method (18.6%), and the empiric value (26.5%)

♦ Safety: Regression formula and total daily insulin dose methods underestimated basal rates (median error -9.17% and -10.06, respectively); the empiric value and weight-based methods overestimated basal rates (6.67% and 11.1%, respectively)

• T2DM:

♦ Only the total daily insulin dose method showed a significantly positive correlation with final basal rates (P<0.001)

♦ Accuracy: Regression formula was most accurate (absolute percentage error 11.4%), followed by the total daily insulin dose method (21.6%)

♦ Overall, the regression formula was significantly more accurate, but the total daily dose of insulin method was “marginally” safer

For T1DM, the authors concluded that the current method based on the total daily insulin dose is the safest and most accurate for estimating basal insulin infusion rates when initiating pump therapy. This formula is: estimated basal rate = 0.75 x (total daily dose of insulin)/2 x 1/24.

In T2DM, the authors concluded that the newly developed regression formula may provide a more accurate estimate than using the total daily insulin dose method. The new regression formula is: basal rate = 0.022 x (TDD) + 0.33

The authors highlighted the preliminary nature of these findings. A larger study is required before any recommendations can be made for clinical practice based on this new formula, they mentioned. They also pointed out several limitations, as well as the inexactness of all methods in this comparison. 

“The observation of frequent basal rate overestimations in all methods and major inaccuracies in a small number of outliers underscores the importance of expert judgment when determining initial basal rates,” they emphasized, “Basal insulin rate estimators are provided only as a tool; with knowledge of each estimate method’s strengths and weaknesses, trained healthcare professionals are better equipped to safely bridge the gap between old and new insulin therapies.”

Take-home Points

• A preliminary retrospective study that compared four different methods of estimating starting basal insulin infusion rates when transitioning to pump therapy found that the currently recommended totally daily insulin dose method is the safest and most accurate in type 1 diabetics.

• Weight-based methods are not as safe or as accurate as total daily insulin dose methods for determining starting basal insulin infusion rates for insulin pump transition in T1DM and T2DM

• A newly developed “regression formula” for determining starting basal insulin rates may be the most accurate in patients with T2DM.

• All methods frequently overestimated basal rates, highlighting the importance of sound clinical judgment when determining initial basal insulin rates while transitioning to pump therapy. 

Reference: Chow N, et al. Determining starting basal rates of insulin infusion for insulin pump users: a comparison between methods. BMJ Open Diabetes Res Care. 2016 Mar 1;4(1):e000145.