Blood is composed of cells and plasma (or serum), a liquid that is normally pale yellow in colour and transparent. Devices that analyze serum specimens (biochemistry tests) monitor three aspect of the serum: lipemia, icterus index and hemolysis index.
Icterus (or the icterus index) is a measure of the yellow colour of serum. This colour is normally due almost exclusively to the presence of bilirubin, a hemoglobin waste product from the red blood cells. The icterus index is expressed as a number of “plus” signs (from zero to ++++). An icterus index of zero is normal. A non-negative result (+ to ++++) indicates a concentration of bilirubin above the normal value. To better understand what these results mean, see your bilirubin result. Very high results (++++) can interfere with certain laboratory tests. More rarely, a high icterus index can be caused by excessive consumption of foods like carrots or vitamin supplements containing beta carotene.