A new high-sensitive nephelometric method for assaying serum C-reactive protein based on phosphocholine interaction

Background: The measurement of C-reactive protein (CRP) concentrations has been of interest as a classical marker of acute phase response; in addition, it has been of particular interest in cardiovascular risk stratification where high-sensitive measurements are necessary. Since CRP is able to bind phospholipids (mainly phosphocholine) in the presence of calcium ions, we explored the possibilities of developing a high-sensitive affordable nephelometric CRP assay based on diluted soy oil emulsions. Methods: Serum (or heparinized plasma) was mixed with Intralipid 20% in Tris-calcium buffer (pH 7.5). After 12 min of incubation at 37 degrees C, the CRP-phospholipid complexes were measured by nephelometry (840 nm) using a BN II nephelometer (Siemens). Results (n=97) were compared with those obtained using a typical immunoturbidimetric method (Roche). Results: Imprecision of the functional nephelometric assay was evaluated using three human serum pools. Within-run coefficients of variation (CVs) for level 1, 2 and 3 were 6.1%, 4.7% and 4.5%, respectively, and between-run CVs were 17.6%, 18.8% and 11.3%, respectively. Good agreement was obtained between the functional nephelometric and the immunoturbidimetric CRP assay in a concentration range from 0.1 mg/L to 50 mg/L (r=0.884). A logit-log calibration curve was made between 0.056 mg/L and 1.785 mg/L. The limit of detection was 0.5 mg/L. Conclusions: The functional nephelometric CRP assay allowed high-sensitive CRP determinations in serum and plasma. Since the assay is species independent, the described functional CRP assay could be used for veterinary purposes as well

Nationwide Harmonization Effort for Semi-Quantitative Reporting of SARS-CoV-2 PCR Test Results in Belgium.

From early 2020, a high demand for SARS-CoV-2 tests was driven by several testing indications, including asymptomatic cases, resulting in the massive roll-out of PCR assays to combat the pandemic. Considering the dynamic of viral shedding during the course of infection, the demand to report cycle threshold (Ct) values rapidly emerged. As Ct values can be affected by a number of factors, we considered that harmonization of semi-quantitative PCR results across laboratories would avoid potential divergent interpretations, particularly in the absence of clinical or serological information. A proposal to harmonize reporting of test results was drafted by the National Reference Centre (NRC) UZ/KU Leuven, distinguishing four categories of positivity based on RNA copies/mL. Pre-quantified control material was shipped to 124 laboratories with instructions to setup a standard curve to define thresholds per assay. For each assay, the mean Ct value and corresponding standard deviation was calculated per target gene, for the three concentrations (10, 10 and 10 copies/mL) that determine the classification. The results of 17 assays are summarized. This harmonization effort allowed to ensure that all Belgian laboratories would report positive PCR results in the same semi-quantitative manner to clinicians and to the national database which feeds contact tracing interventions