Blood Group: Kidd
Common: 23% Caucasians, 8% Blacks, 27% Asians are Jk(a-b+) and at risk for developing anti-Jka .
Causes HDN: Yes
Critical Titer: 1:16
The cases where anti-Jka has caused a problem are few and far between. Of the 4 cases of HDN from anti-Jka mentioned in the article, only 2 required exchange transfusion. After two intrauterine deaths from anti-Jka, the authors treated the infant with immediate exchange transfusion upon birth. 
While anti-Jka is usually mild, it can cause severe HDN. In this article, despite exchange transfusion at 3 days old, the infant developed kernicterus. The authors again recommend early exchange transfusions with anti-Jka to avoid Kernicterus. 
Kidd antibodies are frequently difficult to detect. This makes them hazardous in transfusion medicine. They are a suspected common cause of delayed hemolytic transfusion reactions. 
Kidd antigens are also found on the kidneys . With anti-Jka, titers vary over time or may completely disappear, but they are known to surge at a second exposure to cause delayed hemolytic transfusion reaction (DHTR) .
In one article, out of 20 cases of anti-Jka, 16 required monitoring with titers only, while 4 were followed with more diagnostic tests. One pregnancy with the highest titer of 1:32 had an elevated MCA PSV and needed 4 IUTs. A second pregnancy with titers 1:32 had an infant who needed phototherapy to read the HDN. None of the other 18 infants required any therapy for HDN. The article concluded that the 1 severe case of HDN was correctly identified by following titers and MCA scans as used for montioring anti-D. The authors reported that the criteria used for monitoring anti-D affected pregnancies were effective in detecting severe HDN due to anti-Jka. 
11 - https://www.ncbi.nlm.nih.gov/pubmed/557194