A critical appraisal of current practice in the detection, analysis, and reporting of cryoglobulins

To assess current practice in the detection, analysis, and reporting of cryoglobulins, a questionnaire was sent to 140 laboratories. Only 36% of laboratories used standard procedures (tube preheating, transport in container, and sedimentation and/or centrifugation at 37 degrees C) to ensure that the temperature did not drop below 37 degrees C until after serum separation. Time periods allowed for cryoprecipitation at 4 degrees C varied from 12 h to 9 days, with 30% of laboratories allowing precipitation for <3 days. After cryoprecipitation, 81% of laboratories resolubilized the cryoprecipitate at 37 degrees C, and 77% further immunotyped the cryoprecipitate. After analysis, 5% referred the sample for confirmation, 58% provided a nonquantitative report, and 37% reported the cryoglobulin concentration in the cryoprecipitate as cryocrit, total protein concentration, and/or immunoglobulin concentration. Only 3 laboratories (2%) provided cryoprecipitate-specific reference values for total protein content, and none provided reference values for immunoglobulins. We believe standardization is needed for cryoglobulin detection to avoid missed diagnoses and improve the comparability of results. Laboratories should ensure that sample temperature does not drop below 37 degrees C until after serum separation. The serum should cryoprecipitate at 4 degrees C for at least 3 (preferably 7) days. The cryoprecipitate should be washed and resolubilized at 37 degrees C for further analysis.status: publishe

Establishment of reference values for immunoglobulins in the cryoprecipitate

Cryoglobulins are often estimated by determining cryocrit or total protein content in the cryoprecipitate, but these are only indirect measures. Direct quantification of immunoglobulins in combination with agarose gel electrophoresis, to appreciate the presence of other proteins in the cryoprecipitate, offers a more sensitive and specific tool for confirming the diagnosis of cryoglobulinemia. Using such strategy, we established reference values for immunoglobulins in cryoprecipitate in diseased controls and applied them to 214 consecutive patients. The 97.5th percentile for IgA, IgG and IgM in diseased controls was 2, 11 and 26 mg/L serum, respectively. The distribution of the 49 positive patients (23%) was 10% type I, 33% type IIa, 16% type IIb, and 41% type III. Complement C4 was decreased in 61% and 55% of the patients classified as type II and type III compared to 16% of the patients that were negative for cryoglobulins and 9% of the diseased controls.status: publishe

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