Background: Test 1 is a recently introduced technique claiming to determine Erythrocyte Sedimentation Rate (ESR) in 20 s. In contrast to the original Westergren procedure this new technique uses undiluted blood and operates at 37 degrees C. It is hypothesized that Test 1 is in fact an erythrocyte aggregometer and does not measure any sedimentation.
Methods: Test 1 results were compared to those obtained with StaRRsed, an automated ESR analyser based on the Westergren technique, and the results of both were correlated to various indices of red blood cell (RBC) aggregation, obtained with an aggrego--meter (LORCA). Measurements were made on blood from 75 patients with various rheumatic disorders. Furthermore, blood that was experimentally manipulated in order to affect RBC aggregation, i.e. by changing the hematocrit, by diminishing plasma protein concentration, by inducing hyperaggregation or by RBC rigidification, was tested on all three instruments.
Results: Generally in patient blood, Test 1 results demonstrated a higher correlation with the various aggregation parameters than StaRRsed. Highest correlation (R = -0.8)) with both Test 1 and StaRRsed outcome were seen with I(20), a RBC aggregation parameter directly related to the backscatter intensity. All experimentally induced changes in RBC aggregation paralleled closely those obtained with Test 1 while StaRRsed results followed a different course.
Conclusions: The results obtained in this study strongly support the hypothesis that Test 1 measures only the RBC aggregation process and does not cover any of the indices directly linked to the sedimentation process as determined by the Westergren method.