Neonatal Alloimmune Neutropaenia (NAIN) results most often from maternal alloimmunisation against foetal neutrophil antigens inherited from the father which are different from those present in the mother although the antibodies can also arise as a result of autoimmune diseases such as systemic lupus erythematosus (SLE) or rheumatoid arthritis. The presence of the maternal antibodies in the foetus results in destruction of mature neutrophils in the foetus. New-borns affected by NAIN are almost always neutropaenic at birth with neutrophil counts of less than 0.5 x 10⁹/l for weeks or even months. However, NIAN is often asymptomatic until the children present later with fever, lethargy, skin infections, mucosal and respiratory infections and/or urinary infections. The presence of maternal anti-HNA antibodies in the child’s circulation aids diagnosis of NAIN.

Symptomatic NAIN cases are treated with antibiotics to counter any infections, otherwise treatment is typically with granulocyte colony stimulating factor (G-CSF) to increase neutrophil counts, though many patients improve with no specific therapy.

H&I laboratory investigations of suspected cases of NAIN would involve maternal HNA antibody investigations most commonly by the flowcytometric Granulocyte Immunofluorescence Test (GIFT) and/or the Monoclonal Antibody Specific Immobilisation of Granulocyte Antigens (MAIGA) test. Antibodies against all the HNA antigens HNA-1a, -1b, -1c, -2a, -3a, -4a and -5a have all been implicated. The father or child may be HNA typed to determine if they express the cogent HNA antigen against which antibodies have been formed.