Hematocrit and Interference Correction

Hematocrit (Hct) and chemical interferences represent the two most significant challenges to the accuracy of electrochemical glucose test strips. Hematocrit bias occurs because red blood cells physically impede glucose diffusion; low Hct leads to falsely high readings, while high Hct leads to falsely low readings. Modern systems correct for this using AC Impedance Spectroscopy, which measures the resistance of the blood sample to estimate RBC volume and algorithmically adjust the final glucose value.

Interference is categorized into enzymatic and electrochemical types. Enzymatic interference involves the enzyme reacting with non-glucose sugars; notably, GDH-PQQ strips cross-reacted with maltose (common in dialysis patients), leading to fatal insulin dosing errors. The industry has largely shifted to GDH-FAD or GDH-NAD enzymes to eliminate this risk. Electrochemical interference involves substances like acetaminophen or Vitamin C oxidizing at the electrode. This is mitigated by using low-potential mediators (Osmium/Ruthenium) and multi-electrode designs that subtract background noise from the glucose signal.