Thread by @TransfusionWM

Saturday lunchtime #blooducation tweetorial, inspired by someone who came to see me recently. Let's talk Rh null! (NB written by a clinician, for clinicians…scientists please do chip in!)

The Rh protein comprise Rh D C c E and e. “d” does not exist but is used to denote the absence of D. The C/c and E/e proteins are encoded by the RHCE gene and thus inherited together. Rh associated glycoprotein (RhAG) is required for expression of D and CE.

C/c and E/e are antithetical. Antithetical means a pair of antigens that are coded by different alleles of a single gene It does NOT mean that only one is ever carried on a single RBC.

The Rh null phenotype occurs when neither D, C/e or E/e antigens are expressed. Causes include deletions or mutations of the RhAG gene. Red cells also lack LW and Fy5 and show weak expression of S, s, and U antigens

Patients who are Rh null may make anti-RhAG (following stimulation). This is an antibody to a high frequency antigen (HFA). High frequency (or public) antigens are strictly those occurring on the red cells of >90% of the population, but most are >99%.

Finding blood for these patients is tricky- only donors with Rh null themselves will lack the RhAG protein.

The Rh null phenotype is a red cell membrane disorder, hence patients commonly have a chronic low grade haemolytic anaemia with stomatocytes and spherocytes. I say ‘commonly’, but the phenotype is so rare it has not been well studied! <1 in 6 million people are thought to have it

Patients with Rh null do not make good donors! If no alloantibodies are present, patients can be transfused with ABO and kell matched blood.

If they have antibodies to some of the Rh antigens then give antigen negative blood as far as possible...

...If this isn’t possible (e.g. anti E and anti e) use “least incompatible” ABO and kell matched blood, neg for any other antigens the patient has antibodies to, and consider using IVIg and methylprednisolone.

And of course, speak with your @NHSBT consultant! Blood may need to be sourced from the national frozen blood bank, from the rare donor panel or even internationally.

@NHSBT As an aside, #haemSpRs may be interested to note that a standard group and screen will not identify patients who are Rh null, until they develop antibodies, or unless there is reason to undertake a full Rh phenotype!

@NHSBT Nice review of the Rh blood group system from @BloodJournal here bloodjournal.org/content/95/2/3…

@NHSBT @BloodJournal And a review of the Rh null phenotype here (this paper is almost as old as me!) bloodjournal.org/content/bloodj…