I was convinced that my haemoglobin had dropped, so I persuaded King's to do a blood test half way between appointments at haematology outpatients and sure enough it had fallen to 81. Two pouches of blood were prescribed starting at 14.00 yesterday, but when I arrived they weren't ready. The first pouch wasn't started until 16.30, finishing at 19.35, so I had to come back for the second at 08.30 this morning.
As a pouch takes roughly three hours they wouldn't have been able to fit the second one in even if they had started promptly at 14.00. There is also half an hour or so getting the canula into the arm - it took three goes with the first pouch - and fetching the pouch from the blood bank.