Whereas Jk(b)-related haemolytic disease of the newborn (HDN) is relatively common, HDN due to anti-Jk(a) is very rare, with the total number of cases with complete laboratory findings being just three. Moreover, case reports that occurred in Asia are even rarer due to the low Jk(a) allelic frequency.
Therefore, we were unable to find any data about how long the antibody would persist, when the haemolysis would resolve or how long we should follow-up after discharge. Although it is clear that the causative alloantibodies would eventually become undetectable, this phenomenon could result in a delayed haemoglobin recovery and might require close serological follow-up.
Here, we describe a Korean neonate with severe anaemia, early-onset hyperbilirubinaemia, low haemoglobin and spherocytosis due to anti-Jk(a) antibodies (Table 1). The infant was delivered to a gravida 1, live birth 1, woman without any history of transfusions.
|0.2–12.0 mg/dL||0–0.2 mg/dL||5–40 mg/dL||13.0–20.0 g/dL||1.0–5.0%||−||−||−||0–2 RBCs|
On admission at 2 days of life, the patient appeared healthy with the exception of a generalised palor and mild jaundice, but jaundice progressively worsened. Numerous spherocytes were also found on peripheral blood smears. Further serological testing revealed a strongly positive direct antiglobulin test (DAT) and a weakly positive indirect antiglobulin test (IAT). Additionally, the infant's DAT was found to be moderately reactive with both monospecific immunoglobulin G and C3d present on red blood cells (RBCs).
Anti-Jk(a) was able to be identified in the patient's serum via irregular antibody identification studies using 11 panels of RBCs. Consequently, Jk(a) antigen of the neonate's RBCs was confirmed using monoclonal anti-Jk(a) antibodies. To clearly show that the DAT positivity was caused by anti-Jk(a), the antibodies adherent to patient's RBCs were eluted and secondarily confirmed by antibody identification panels.
Anti-Jk(a) antibodies were also isolated from the maternal serum. Antigen typing of paternal RBCs was then performed by monoclonal antibodies, revealing a positive Jk(a) antigen.
Following intensive phototherapy from day 3 to 5, the total bilirubin had dropped to 5.7 mg/dL by the 12th day. Nonetheless, the haemoglobin level had dropped to 7.5 g/dL at this time without transfusion.
At a follow-up visit on the 51st day, his haemoglobin level was still relatively low, probably because anti-Jk(a) antibodies were still found to adhere to the patient's RBCs despite IAT negativity.
In the case of alloimmunization (i.e. not passive transfer from mother to fetus), the persistence rates were observed to be 57%, even after a relatively long follow-up period. In the case described here, the passively transferred antibody disappeared from the neonate's blood by day 51. However, the antibodies adherent to the RBC membrane remained detectable until that time. Therefore, we contend that in such cases, it is necessary to monitor haemoglobin levels during the first months of life after discharge.