Red cell alloimmunisation and finding compatible blood

What it is

When the blood bank calls to say that the patient's investigations are abnormal and that finding compatible blood will likely require time, that is itself a finding. What it implies is the presence of acquired antibodies, that is, a +ve Ab screen test. And the rule that follows: the more the acquired Ab in recipient plasma, the more difficult it is to find a compatible blood unit that is Ag-negative for those Abs.

How it presents

The case is a 33 years old sickle cell disease patient admitted with hemolytic crisis. He was on regular follow-up in another hospital, and he was referred because compatible blood could not be found in his primary institution. This was his first admission in your hospital.

Complete blood count: hemoglobin 5 g/dl (11.5-15.5); white blood cell count 8.4 X10^9/L (2.2-10.0); platelet count 220 x 10^9/L (150-450). Historical blood bank investigations: nil. Two units of red blood cells were ordered.

How it is diagnosed

The blood bank must identify the acquired antibodies first, and then select an Ag negative unit for those specific antibodies, to prevent hemolysis. Cross matching is the other investigation named.