The Capillary-Tube Method of Rhesus Testing

Abstract

Chown''s capillary tube method of rhesus testing is evaluated, special attention being paid to the sources of error. The method is worthless unless saline agglutinating serums and saline suspensions of cells are used. False negative results occur if weak serums, dilute (less than 15%) suspensions of cells, or cells more than 4-5 days old are used. False positives occur if cells are suspended in protein-rich media. In a direct comparison between tube and capillary method using low titer saline agglutinating serum and a saline suspension of cells, no false positives were obtained in 150 trials and 3 false negatives in 254 trials; 2 of these false negatives occurred with a dilute (10%) cell suspension of 6-day-old cells. Using the capillary method for rhesus testing and a tile method for ABO grouping, the groups of 10,000 unselected expectant mothers living in n.-w. London were detd. The results were:- 17.22% rhesus-negative; Group O, 45.78%; Group A, 42.19%; Group B, 8.90%, Group AB, 3.13%. The results are homogeneous and agree, within the limits of statistical variation, with those obtained by other workers using standard methods.