How do you manage a patient that has anti Kna? Do you give "incompatible" units? Do you crossmatch however many units it takes to find "compatible" units? How do you make sure that the anti Kna is not masking other more significant allo antibody(ies)?

How do you manage a patient that has anti Kna? Do you give "incompatible" units? Do you crossmatch however many units it takes to find "compatible" units? How do you make sure that the anti Kna is not masking other more significant allo antibody(ies)?

Antibodies within the Knops Blood Group System are not considered to be clinically significant (if you disregard the papers written by Molthan, as most people do), and so, yes, you would give incompatible units. You would have to cross-match an awful lot of units to find sufficient Kn(a-) units - and even then you cannot be sure that they are really Kn(a-). Kn(a) antigens vary immensely from individual to individual, quotes having been made from just 20 sites per red cell to 1, 500 sites per red cell, but, in addition, the Kn(a) antigen "goes off" during storage, so compatible units may well not really be Kn(a-) anyway.

When one of our hospitals has a patient with anti-Kna, they always send us a sample so that we can test it with a battery of red cells from donors that have been tested with a strongish anti-Kna (quite rare), so that we can exclude on these cells (it also helps to know the patient's "full" cell type, so that you know what else they can possibly make.

We have found, though, that other specificities that are present with anti-Kna are usually stronger than the anti-Kna itself, and so they are easily recognised.

Hope that helps.

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