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A Critical Appraisal of Current Practice in the Detection, Analysis, and Reporting of Cryoglobulins

¹ Department of Laboratory Medicine, Immunology, University Hospitals Leuven, Catholic University of Leuven, Belgium; ² Current address: Department of Laboratory Medicine, Ziekenhuis Oost-Malle, Zoersel, Belgium; ³ United Kingdom National External Quality Assessment Service (UKNEQAS), Department of Immunology, Sheffield, United Kingdom.

^aAddress correspondence to this author at: Laboratory Medicine, Immunology, University Hospitals Leuven, Herestraat 49, B-3000 Leuven, Belgium. Fax 0032-16-34-79-31; e-mail Xavier.bossuyt{at}uz.kuleuven.be.

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 °C) to ensure that the temperature did not drop below 37 °C until after serum separation. Time periods allowed for cryoprecipitation at 4 °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 °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 °C until after serum separation. The serum should cryoprecipitate at 4 °C for at least 3 (preferably 7) days. The cryoprecipitate should be washed and resolubilized at 37 °C for further analysis.