A-119 Lipemia Interference
Authors: Berman M , Hayes J 
Published: October 2024

Abstract

Background
Lipemic specimens is a common problem in clinical laboratories. Analytical results may be perturbed by lipemia, leading to misdiagnosis and unnecessary treatments for patients. Serum index testing is an important preanalytical test for assessing the potential effect of endogenous HIL interferents (hemoglobin (H), bilirubin (I) or lipids (L)) on test results. Automated HIL systems are not standardized and differ in their response. HIL induced interference should be verified by all clinical laboratories. Intralipid, a commercial lipid emulsion with particle size ranges from 200 to 600 nm is often used to verify the L index. However, intralipid lacks particles that mimic large VLDL, as well as the lower and upper ranges for chylomicrons size. In contrast, patient samples contain a complex mixture of macromolecular lipid and protein structures. Therefore, lipemia induced by Intralipid is not identical to lipemia in patient serum samples. The purpose of this study is to increase awareness of lipid interference and demonstrate the relationship of a lipid L Index to intralipid and triglyceride interference.

Methods
A set of 16 panels were prepared from a commercially available Triglyceride rich Lipoprotein material. These panels spanned a lipid concentration from 0 to 3000 mg/dL. Panels were tested on the Alinity c and ARCHITECT c8000 TRIG2 assays (04U0615 and 04T1016 respectively) on 2 reagent lots in a single run to determine the Triglyceride concentration. Then these samples were assessed for an HIL L score using the Abbott HIL saline protocol.

Results
The relationship between the Triglyceride rich Lipoprotein and the L Index was linear with a high correlation (r= 0.999) for Alinity and ARCHITECT respectively. The L Index underestimated the Triglyceride Rich Lipoprotein concentration. The reason for the lower estimate of Triglyceride rich lipoprotein specimens on an L Index is likely due to the differences in size of the lipid particles between the two artificial lipid materials, Intralipid and Triglyceride rich lipoprotein. In addition, while the triglyceride assay provides a quantitative measurement of the lipemic concentration, the L Index is designed to provide an estimated result.

Conclusions
Intralipid is an acceptable material used to verify spectrophotometric HIL systems. The L Index provides an estimate of sample turbidity, not the concentration of Triglyceride. Vendor purchased human derived Triglyceride rich lipoprotein, which contains a heterological mixture of lipid particles, may be regarded as a more appropriate material for assessing lipid interference. Thus, while recovery of the L Index correlates well to the Intralipid concentration, it can have a poorer correlation with vendor purchased samples containing Triglyceride due to the different vesicle sizes in these materials. This study demonstrates the Triglyceride rich material used to assess lipid interference in Sigma Strong assays provides a difference in response between the Triglyceride concentration of this material determined on a Triglyceride assay vs the L Index. The choice of lipemic material to use, (eg. artificial, native), can influence the results. Thus, care should be taken in comparing results for these materials.