Abstract
Dear Sir,
In the era of evidence-based laboratory medicine, the recent review of cryoglobulin laboratory evaluation 1 makes recommendations that, in my view, are inappropriate for many laboratories. The recommendations that ‘Detailed characterisation and typing of the cryoprecipitate should always be performed’, and that quantitation of the cryoglobulin needs to be done on all specimens, need to be backed up by evidence that these procedures will actually alter patient management and benefit patients.
Typing and quantitation are labour-intensive, and involve extensive manual handling of specimens that are often highly infectious. In our laboratory the vast majority of cryoglobulins are found in patients who are known to have hepatitis C; the clinical question being asked is simply ‘does this patient have a cryoglobulin which can explain their symptoms?’ and typing or quantitation of the cryoglobulin adds nothing to their management. We have a simpler protocol: after three days at 4°C, the presence/absence of a cryoglobulin is reported, a protein electrophoresis is done on the 37°C sample, and detailed further analyses are performed only if requested by the clinicians. This has proved perfectly satisfactory, and we get very few requests for typing or quantitation.
In addition, the recommendation that precipitation needs to be continued for seven days is not backed up by any evidence. It has always seemed highly unlikely that a cryoglobulin which only precipitates after more than three days at 4°C would have any chance of precipitating in vivo. I suspect that such late-precipitating cryoglobulins are an incidental finding and do not relate to clinical effects in the patient, and I have never seen any evidence to contradict this common-sense view.
Laboratory practice in the real world is constrained by resource limitations, and good laboratory practice entails optimizing resource allocation, and not always performing all possible tests that may be appropriate in a reference laboratory.
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