Utilisation of intravenous immunoglobulin in New Zealand: a clinical audit

To identify what diagnoses account for the utilisation of intravenous immunoglobulin (IVIG) in New Zealand (NZ), to establish regional differences in prescribing patterns, and to audit the appropriateness of its use in a subset of patients.

We accessed NZ Blood Service and NZ Health Information Service data to retrospectively determine the quantities of IVIG issued by each District Health Board (DHB) during 2004 and the diagnoses associated with each treatment episode. DHB-of-domicile data was used to explore the influence of cross boundary flow of patients. In a further prospective audit performed over 6 months we collected data on all utilisation of IVIG in eight DHB. The indications for IVIG were checked for compliance with the Australian Health Minister's Advisory Council (AHMAC) and Auckland District Health Board (ADHB) guidelines.

Retrospective audit--The rates at which IVIG was prescribed varied 11-fold across the different DHB, from 100.5 g/1000 population in Capital and Coast DHB to 8.8 g/1000 in Nelson-Marlborough DHB. With cross-boundary flow analysis, the rates at which the residents of different DHB received IVIG (from any DHB) varied 10-fold. The Auckland DHB (and to a lesser extent some other DHB) provided substantial amounts of IVIG to treat patients resident in other DHB. Eccentric patterns of utilisation (e.g. obstetric) were found in some regions. Prospective audit--We captured 466 treatment episodes. Primary antibody deficiency was by far the most frequent diagnosis. Five diagnoses accounted for 69% of the total IVIG utilisation. 80.6% of the diagnoses were in AHMAC category 1 (convincing evidence of benefit) and 71.5% were approved diagnoses in the ADHB guidelines. Compliance with the two sets of guidelines varied significantly across the different DHB.

A limited set of disorders accounts for most of the IVIG prescribed in NZ. The wide variation in the patterns of utilisation in different regions is probably due to a range of factors and could usefully be studied further. There is almost certainly under- and over-utilisation in some regions for certain diagnostic categories. Up-to-date, evidence-based guidelines and a rigorous authorisation process have the potential to promote appropriate utilisation.