The effect of paraproteins on the erythrocyte sedimentation rate: a comparison between the StarrSed and TEST 1.

BACKGROUND The principle of the erythrocyte sedimentation rate (ESR) as assessed by TEST 1 is different from that of Westergren-based methods. This could result in different influences on the tests by paraproteins. METHODS We investigated the effect of paraproteins on ESR readings by TEST 1 (y) and the StarrSed (x), a Westergren-based method, in 142 patients with paraproteinaemia. Agreement (Passing-Bablok) and bias (Bland-Altman) between methods was investigated and compared with that of a control population. RESULTS A poor agreement between the two methods was found in patients with a paraprotein (y = 0.67x + 3.3) in comparison with that of the control population (y = 0.96x + 0.2). Large differences between methods were present when ESR readings were >40 mm/hour, but clinical interpretation was similar in 90% of cases. Linear regression showed a concentration dependent influence of paraproteins on ESR readings by the StarrSed, especially for immunoglobulin class IgM. CONCLUSION ESR readings by TEST 1 result in similar clinical interpretation for most subjects, but readings are less influenced by the presence of a paraprotein than those of a Westergren-based method.