Reevaluating the Icterus Index Cutoff of a Jaffé Creatinine Method

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Analytical Chemistry

Background:

• The Roche Jaffé method is widely used for creatinine measurement.
• Icterus, indicated by elevated bilirubin levels, can interfere with creatinine assays.
• Current icterus index cutoffs for the Roche Jaffé method may be overly conservative.

Purpose of the Study:

• To redefine the icterus index cutoff for the Roche Jaffé creatinine method.
• To evaluate interference from both conjugated and unconjugated bilirubin.
• To assess performance across multiple Roche cobas analytical modules.

Main Methods:

• Interference was evaluated by spiking pooled plasma with known concentrations of conjugated and unconjugated bilirubin.
• The Roche Jaffé method was performed on Roche cobas c311, c501, and c701/c702 modules.
• Absolute and percentage errors were calculated, with allowable error limits set at 0.1 mg/dL.

Main Results:

• No significant bias exceeding allowable error limits was observed.
• Acceptable performance was maintained up to a conjugated bilirubin icterus index of 16.2 and unconjugated bilirubin icterus index of 18.5.
• These findings exceed the manufacturer's recommended cutoffs of 5 and 10, respectively.

Conclusions:

• The Roche Jaffé creatinine method demonstrates robust performance in the presence of icterus at elevated bilirubin concentrations.
• The study supports higher icterus index cutoffs for this method.
• Hospital system icterus index cutoffs were updated to 16 for conjugated and 18 for unconjugated bilirubin.