1 Department of Chemical Pathology, Faculty of Health Sciences, University of Pretoria and National Health Laboratory Service Tshwane Academic Division, Pretoria, South Africa.
2 Division of Chemical Pathology, University of Cape Town, Cape Town, South Africa.
3 Clinical Chemistry, St. Vincent's University Hospital, Donnybrook, Dublin, Ireland.
4 School of Medicine, University College Dublin, Belfield, Dublin, Ireland.