All laboratories performed visual observation of the cryoprecipitate. Most laboratories (72%) compared the same sample at different temperatures and approximately 1 in 3 laboratories (32%) compared serum and plasma.
There was wide variation in the type of results reported, ranging from a simple qualitative negative/positive result to a quantitative report including cryoglobulin type and total protein content and/or immunoglobulin concentration in the cryoprecipitate. Of the 127 laboratories included for the postidentification phase, 50 (39%) reported the cryocrit, the total protein content, and/or the immunoglobulin concentration in the cryoprecipitate (quantitative); 48 (38%) answered negative/ positive only; and 29 (23%) provided additional information without reporting the cryoglobulin concentration in the cryoprecipitate (nonquantitative).
Forty-six of the 50 laboratories that provided a quantitative report and 55 of the 77 laboratories that provided a nonquantitative report performed immunofixation analysis on the cryoprecipitate. Of the 101 laboratories (57%) that further immunotyped the cryoprecipitate, 98 performed immunofixation or immunoelectrophoresis, and 3 used protein electrophoresis only.
For type I cryoglobulins, which are often present at concentrations >5 g/L, (1), reporting the presence or absence of an important visual cryoprecipitate that can be resolubilized is acceptable.
Of the 11 laboratories that provided reference values, only 3 (2%) applied cryoprecipitate-specific reference values, whereas the other 8 used reference values for serum proteins and/or immunoglobulins, which are not valid for the cryoprecipitate. Three laboratories that had cryoprecipitate-specific reference values provided different reference values using total protein content: 0-10 mg/L serum (no reference provided), 0-50 mg/L serum (no reference provided), and 0-80 mg/L (12).
Although several authors have looked at total protein content in the cryoprecipitate to establish reference values, (12, 14, 15), only 3 laboratories (2%) provided cryoprecipitate-specific reference values for total protein content.