CRYOGLOBULIN

Cryoglobulins are abnormal immunoglobulins that precipitate in cold temperatures and dissolve on warming. They form immune complexes that activate complement and deposit in small- to medium-sized vessels, causing vasculitis, endothelial injury, impaired blood flow and tissue ischemia. Clinically they’re linked to purpura, arthralgia, neuropathy and glomerulonephritis, often associated with infections, autoimmune disease, or lymphoproliferative disorders.

A cryoglobulin blood test detects abnormal proteins (cryoglobulins) that clump when cooled. It’s used to diagnose cryoglobulinemia and investigate symptoms such as cold-induced skin discoloration, numbness, ulcers, unexplained low blood counts, or kidney problems. The test helps identify underlying causes (autoimmune disorders, infections like hepatitis C) and monitor response to treatment.

Cryoglobulins are linked to chronic infections (especially hepatitis C, also hepatitis B and HIV), autoimmune diseases (Sjögren’s syndrome, systemic lupus erythematosus, rheumatoid arthritis), lymphoproliferative disorders (Waldenström’s macroglobulinemia, multiple myeloma, B‑cell lymphomas), and cryoglobulinemic small‑vessel vasculitis. They can also occur with chronic liver disease and occasionally after certain infections or medications.

A positive cryoglobulin test means abnormal proteins (cryoglobulins) are present that precipitate at cold temperatures. They can cause immune-complex–mediated small‑vessel inflammation, producing purpura, joint pain, neuropathy and kidney involvement, and often indicate underlying infections, autoimmune disease or lymphoproliferative disorders. Further evaluation (cause search, complement, renal tests) and clinical correlation are needed. Proper sample handling (kept warm) is important to avoid false results.

Vasculitis is inflammation of blood vessels. Many forms are autoimmune—where the immune system mistakenly attacks vessel walls (for example ANCA-associated vasculitis and giant cell arteritis)—and are treated with immunosuppressants. However, some vasculitis cases are secondary to infections, drugs, or malignancy rather than autoimmune causes. Diagnosis and treatment depend on the specific type, severity, and organs involved.

Rheumatoid factor (RF) is an autoantibody—most commonly IgM against the Fc portion of IgG—and is not itself a cryoglobulin. Cryoglobulins are immunoglobulins or immune complexes that precipitate in the cold. However, RF can be a component of cryoglobulins; mixed cryoglobulinemia often contains an IgM RF complexed with IgG, so RF may contribute to cryoglobulinemia.