Blood Group: Kell

Common: ~98% of the population is U1a - and could develope anti-U1a. [1]

Causes HDN: Yes
Critical Titer: 1:8
In 1994 the first case of HDN due to anti-U1a was reported. The infant had a positive direct coombs test and severe anemia. Jaundice was not severe enough to need phototherapy or an exchange transfusion, but a regular blood transfusion was performed for the anemia. [2] 

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