Evaluation of International Normalized Ratios by a controlled field survey with 4 different thromboplastin reagents - Kazama, M; Suzuki, S; Abe, T; Tahara, C; Shimazu, C; Akiyama, Y; Higashi, K; Ishiguro, I; Kimura, T; Motoi, S; Tsukai, K; Kobayashi, M; Niwa, Y; Makita, H; Yasumuro, Y; Nakatake, T (Thromb Haemostas, 1990)