In the March 2002 issue of Clin Chem, the NACB published a 36 page report about the use of laboratory tests for patients with diabetes. It's probably the longest paper ever published by Clin Chem. Dr. Westgard examined the "evidence-based" recommendations, though, and found some poor Sigma values. Here, using EZ Rules software, Dr. Westgard demonstrates the process of choosing QC for GHb.