Blood separation systems and methods are provided for detecting lipids in plasma that has been separated from a plasma-containing fluid, such as blood. The system includes a fluid processing region in which a plasma-containing fluid is separated into plasma and other fluid components. A plasma flow path is associated with the fluid processing region for the flow of at least a portion of the separated plasma into or out of the region. A lipid detector shines blue and/or ultraviolet light through the separated plasma in the plasma line to optically detect the presence of lipids therein. The lipid detector may be used alone or in combination with a hemoglobin detector to reduce the number of false hemoglobin alarms or an interface detector for improved detection and correction of the location of an interface between separated fluid components in the fluid processing region.
