Thrombocytosis of active rheumatoid disease. Ann Rheum Dis

SUMMARY Two cross-sectional and one longitudinal study of patients with rheumatoid arthritis showed that platelet number correlated with both clinical and laboratory parameters of disease activity, including erythrocyte sedimentation rate, zeta sedimentation ratio, viscosity ofplasma and blood, white cell count, liver enzymes, rheumatoid factor, and several acute-phase proteins. There was also an inverse relationship between platelet number and the haemoglobin and serum albumin levels. "'IIndium-labelled platelet survival was reduced in 4 patients with active rheumatoid arthritis despite a raised platelet count, with labelled platelets being localised to inflamed joints in the 2 patients studied. Platelet aggregation was normal. We suggest that the raised platelet count of active rheumatoid arthritis may be a useful index of disease activity and may represent a bone marrow stress (syndrome) response to shortened platelet survival, with platelet sequestration occurring in areas of synovial inflammation. Platelet counts are usually monitored in patients with rheumatoid arthritis (RA) to detect adverse reac-tions to drugs such as gold and penicillamine, but the platelet may also be directly involved in the disease itself. In 1972 Selroos ' noted that many patients with RA had a high platelet count, and Hutchinson et al.2 subsequently showed a relationship between platelet number and some indices of disease activity. Many haematological, immunological, and biochemical parameters are abnormal in RA and are related to disease activity,3'- ` but none provide a widely accepted method of assessment in RA. It would be of considerable value to know whether the platelet count provides a useful index of disease activity and why thrombocytosis should occur. We have therefore investigated the relationship of platelet count to clin-ical and laboratory tests of disease activity in RA, and have also investigated platelet survival, aggregation, and localisation in affected joints. Patients and methods PATIENT