Diagnostic Significance of Icteric Index

Background: The pre-analytical errors occur commonly due to the presence of interfering substances like hemoglobin, bilirubin, lipids and paraproteins. Analyzer has the capability to detect them and produce semi quantitative unit less index values, collectively known as serum indices. Interference with bilirubin is estimated as icteric index. Aim of the study is to assess the icteric index of serum samples and to find the correlation with total bilirubin levels. Objective is also to find out whether icteric index can be used as a initial biomarker to decide when total bilirubin estimation is essential.

Methodology: The study was conducted in the Biochemistry Department of Karwar Institute of Medical Sciences, Karwar. Icteric index was measured in 779 patients’ blood samples in the year 2015 using XL-640,Transasia analyzer at 480 nm (primary wavelength) and 505 nm (secondary wavelength). Total bilirubin was also estimated for these blood samples. Receiver operating characteristic curve (ROC) analysis was carried out to determine area under the curve (AUC).

Results: Area under the curve for ROC was 0.814. Sensitivity of the test was 92.4% and specificity was more than 93.2%. Positive predictive value of icteric index is 96.1% and negative predictive value is 82.2%. LR+ is 13.6 and LR- is 0.08. The cut off value of icteric index above which bilirubin levels are considered abnormal (> 1mg/dl) was 58.

Conclusion: The icteric index is a cost effective test and can be safely utilized by laboratories as a screening tool for hyperbilirubinemias.