A subgroup of CHDs can only be treated palliatively through a Fontan circulation. In case of a failing Fontan situation, serum proteins are lost unspecifically and can also lead to a loss of vaccine antibodies. In a failing Fontan situation, heart transplantation may be the only feasible option.

We describe a 17-year-old patient born with a hypoplastic left heart complex, who underwent Fontan completion at the age of 4 years and developed a failing Fontan physiology. Therefore, a Fontan takedown with creation of a reverse 1½-circulation was performed. Multiple exacerbations of protein losing enteropathy occurred with a hypoproteinaemia, hypalbuminaemia, and hypogammaglobulinaemia. The patient was hospitalised several times and treated with intravenous application of immunoglobulins and albumin for symptom control. Before one of this substitutions, the immunoglobulin G against measles, mumps, and rubella was determined: the patient’s serum demonstrated a positive measles and rubella, but mumps was negative. After administration of the iv-therapy, the lacking antibodies were replenished, and there was a positive test for mumps.

Serum samples were analysed by neutralisation test and enzyme-linked immunosorbent assay (ELISA).

Although the patient had been vaccinated according to national guidelines, we saw an intermittent immune deficiency for mumps, but not for rubella and measles. For patient with a failing Fontan circulation, we recommend to test to vaccine antibodies for mumps, measles, and rubella with an ELISA an if its negative with a neutralisation test, especially in view of a possible heart transplantation to find a possible immune deficiency.