Diagnosis of type I cryoglobulinaemia made through identifying crystals in the blood smear

We report a case of type I cryoglobulinaemia in a 52-year-old man who presented with widespread cutaneous necrosis. The diagnosis could not be established early on, as repeated testing for cryoglobulin was negative despite a careful collection method. The diagnosis was made 1 year later, on an incidental full blood smear that revealed crystals, which is an uncommon way to diagnose this condition. We discuss the difficulties we faced in establishing the diagnosis and emphasise the need for repeat cryoglobulin testing in this clinical setting. In such cases, examination of a blood smear should be considered.