Incremental Area Under the Curve (iAUC)

Incremental area under the curve, or iAUC, is a summary measure of how much a measured concentration rises above a baseline value over a specified period. It is commonly used for time-series data such as blood glucose or insulin after a meal or test drink. The concentration is measured at several time points, plotted against time, and the area associated with the increase above baseline is calculated .¹

The calculation is usually performed numerically with the trapezoidal rule because only discrete samples are available. A key feature is that iAUC focuses on change relative to the starting value rather than the entire concentration present in the blood. This makes it different from total area under the curve, which includes the baseline concentration as part of the area .¹

The exact handling of values that fall below baseline must be stated because different conventions can produce different results. In glycemic-response research, a common approach calculates the positive incremental area while excluding area below the fasting baseline. iAUC is therefore not a single concentration or a peak value; it compresses both the magnitude and duration of a response into one number, and its meaning depends on the sampling window and calculation method .¹