The importance of cross-match/transfusion ratio and intervals between successive cross-matches in determining red cell outdate rates.

Measurements have been made of cross-match/transfusion ratios (C/T ratio) and intervals between successive cross-matches on the same units of blood performed in three different major hospitals each providing a wide range of clinical services. Outdate rates were 4%, 15% and 25% respectively and were associated with C/T ratios of 1.3, 2.0 and 2.15. There were corresponding increases (means of 3.6, 4.5 and 5.0 days) in the length of time unused units of blood were left between successive cross-matches. Calculations of outdate rates from the above figures closely predicted the trend shown by observed non-use rates. It has thus been demonstrated that apparently small differences in blood bank practice can produce important variations in the efficiency of use of red cell units.