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.

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.