| B/F | black female; bound/free [antigen ratio] |
|---|---|
| BH/VH | body hematocrit-venous hematocrit [ratio] |
| BRR | Bannayan-Riley-Ruvalcaba [syndrome]; baroreceptor reflex response; breathing reserve ratio |
| BUN/CR | blood urea nitrogen/creatine ratio |
| C/D | cigarettes per day; cup to disc ratio |