Exogenous triglycerides interfere with a point of care CRP assay: a pre-analytical caveat

What is it about?

C-reactive protein (CRP) is an important test for assessing inflammation. Point of care testing (POCT) for CRP in whole blood is popular because of the rapid delivery of results and is convenient for testing children. POC CRP testing is increasingly used in primary care. CRP interacts with phospholipids. On the other hand, exogenous triglycerides containing particles may cause interference in optical assays. We investigated the potential effect of exogenous triglycerides on a CRP POCT reader. CRP was determined in whole blood with the Afinion CRP assay. Purified CRP was spiked to whole blood, in different concentrations. Next, exogenous triglycerides were added to the CRP-spiked whole blood. Intralipid® is a stabilized fat emulsion. The addition of triglycerides increased whole blood POC CRP values. Especially, when exogenous plasma triglyceride concentrations exceeded 9 mmol/L, significant differences in CRP values were observed. In contrast to the simple statement of the manufacturer that triglycerides up to concentrations of 7.8 mmol/L do not affect CRP test results, reality might be more complex. Our data show that the Afinion POC CRP assay is sensitive to interference by high concentrations of exogenous triglycerides. These interferences are due to the lipid particles per se and not to the calcium dependent interaction with CRP. In this study, Intralipid® was used, similar results are to be expected following postprandial hypertriglyceridemia, as postprandially formed chylomicrons show similar properties as Intralipid® particles. In our study, interference on whole blood POC CRP values becomes significant for triglyceride values exceeding 9.0 mmol/L. In most subjects postprandial hypertriglyceridemia is very moderate: peak plasma triglyceride concentrations after ingestion of a fat-rich meal are expected not to cause major interference in this assay. However in dyslipidemia patients, postprandial increase of triglycerides can be very prominent, and therefore cause analytical interference: 0.77% from specimens obtained from the our emergency department had a triglyceride values exceeding 9.0 mmol/L. In contrast to core labs, the operator of POC assays is not warned about the potential presence of exogenous lipids. Although very lipemic samples originating from an emergency department are rare, these interferences do occur and may affect CRP results and thus further treatment of the patient. In case of a postprandial specimen, it can be recommended to send a (confirmatory) sample to the core lab for CRP determination.

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