EXPRESS: Does the use of fish-oil based lipid emulsion in the clinical setting of total parenteral nutrition (TPN) and lipid rescue therapy interfere with common laboratory analytes on Roche Cobas 6000?

Background Lipaemic interference on automated analysers has been widely studied using soy-based emulsion such as Intralipid. Due to the greater adoption of fish oil-based lipid emulsion for total parenteral nutrition in view of improved clinical outcomes, we seek to characterize the optical properties of SMOFLipid 20%(Fresenius Kabi, Bad Homburg, Germany), a fish-oil based emulsion, on the Roche Cobas 6000 chemistry analyser(Roche Diagnostic, Basel, Switzerland). Method Various amounts of SMOFlipid were spiked into pooled seras. We plotted Roche Cobas Serum Indices Lipaemic indices(L-index) against the amount of SMOFlipid added. We then studied the interference thresholds for AST, ALT, Albumin and renal panel analytes using SMOFlipid. We subjected five levels of spiked lipaemia to high speed centrifugation and analysed the specimens pre and post centrifugation. To postulate whether fish-oil based lipid emulsion interferes with laboratory results in the clinical setting, we calculated concentrations of SMOFlipid post lipid rescue therapy and steady state concentration of a typical TPN regime using pharmacokinetic principles. Results SMOFlipid optical behaviour is similar to Intralipid using the Serum indices L-index, with 1mg/dL of SMOFlipid representing 1 unit of L-index. Manufacturer stated interference thresholds are accurate for ALT, AST, albumin, urea and creatinine. High speed centrifugation at 60 min 21100G facilitates the removal of fish-oil based SMOFlipid. Conclusion Based on the interference thresholds we verified and pharmacokinetics parameters provided by SMOFlipid manufacturer, total parenteral nutrition may not interfere with chemistry analytes given sufficient clearance, but lipid rescue therapy will interfere. Further studies assessing lipaemic interference on immunoassays are needed

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