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

Artificially raised creatinine concentrations due to analytical interference for samples contaminated with total parenteral nutrition fluid

BACKGROUND

A sample received in the laboratory from a patient receiving total parenteral nutrition (TPN) indicated that the patient may have renal dysfunction, but the results were not considered to be reliable enough to report. Investigations using a reference method for measurement of creatinine confirmed positive interference in the creatinine assay and distribution of samples via an External Quality Assessment (EQA) Scheme showed that this positive interference was method dependent.

METHODS

Residual TPN fluid (Nutriflex Lipid Special) left in the bag after the patient had completed the infusion was collected and added to a patient serum pool in increasing amounts and distributed to different laboratories for analysis of creatinine and glucose through an EQA Scheme.

RESULTS

Positive interference in a number of different creatinine assays was identified as a result of a component in the TPN fluid. Positive interference from high concentrations of glucose has been demonstrated to be a cause for falsely high results in Jaffe creatinine assays.

CONCLUSIONS

The concern would be that a sample contaminated with TPN fluid would have both abnormal electrolytes and creatinine concentrations and give the impression that the patient was in renal failure due to analytical interference in the creatinine assay and laboratory staff need to be aware of this problem.

Methods to reduce lipemic interference in clinical chemistry tests: a systematic review and recommendations

OBJECTIVES

Lipemia is the presence of abnormally high lipoprotein concentrations in serum or plasma samples that can interfere with laboratory testing. There is little guidance available from manufacturers or professional bodies on processing lipemic samples to produce clinically acceptable results. This systematic review summarizes existing literature on the effectiveness of lipid removal techniques in reducing interference in clinical chemistry tests.

METHODS

A PubMed search using terms relating to lipid removal from human samples for clinical chemistry tests produced 1,558 studies published between January 2010 and July 2021. 15 articles met the criteria for further analyses.

RESULTS

A total of 66 analytes were investigated amongst the 15 studies, which showed highly heterogenous study designs. High-speed centrifugation was consistently effective for 13 analytes: albumin, alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin, creatine kinase (CK), creatinine (Jaffe method), gamma-glutamyl transferase (GGT), glucose (hexokinase-based method), lactate dehydrogenase (LDH), phosphate, potassium, and urea. Lipid-clearing agents were uniformly effective for seven analytes: ALT, AST, total bilirubin, CK, creatinine (Jaffe method), lipase, and urea. Mixed results were reported for the remaining analytes.

CONCLUSIONS

For some analytes, high-speed centrifugation and/or lipid-clearing agents can be used in place of ultracentrifugation. Harmonized protocols and acceptability criteria are required to allow pooled data analysis and interpretation of different lipemic interference studies.