Cryoglobulin evaluation: best practice?

Cryoglobulins are serum immunoglobulins that precipitate at temperatures below 37 degrees C and re-dissolve on warming. Cryoglobulinaemia leads to variable symptoms including characteristic purpura, ischaemia of extremities, renal failure, peripheral neuropathy, abdominal pain secondary to intestinal ischaemia and arthralgias. Cryoglobulin testing is underutilized in clinical practice. It has been neglected in clinical laboratories and by clinicians due to several factors, such as the length of time it takes for serum cryoglobulin analysis to be performed in the laboratory, the perceived difficulty in getting optimal sampling conditions and a failure to appreciate that even apparently low levels of cryoglobulin can be associated with severe symptoms in some patients. The most important variable confounding standardization of cryoglobulin testing is improper sample handling. A recent report critically appraising the current practice of cryoglobulin evaluation in 137 laboratories in Europe by United Kingdom National External Quality Assurance Scheme (UKNEQAS) illustrated the wide variability in practice. Although many clinical laboratories perform cryoglobulin evaluation, there are widespread differences in the methodology used and the care with which this is carried out and this leads to considerable intralaboratory and interlaboratory variability. The most common sources of error are false-negative results due to loss of cryoprecipitate during transport and storage. Better standardization is needed to avoid missed diagnoses and improve the comparability of results. Laboratories should ensure that sample temperature is maintained at 37 degrees C until the serum is separated. In this article, we briefly review the classification and clinical features of cryoglobulins and suggest best practice guidelines for laboratory detection and identification of cryoglobulins.