The Nuffield Trust is developing a commissioning tool that predicts patients' cost to the NHS based on their previous treatment and GP records.
But Dr Peter Holden, GPC negotiator and member of the Advisory Committee on Resource Allocation, said there is 'no way' such a formula can work without being 'incredibly intrusive' for patients. 'If you do this at practice-level, people can identify who you are talking about, and how much they cost the NHS,' he said.
The Nuffield Trust report, Predictive risk and healthcare, described ongoing DoH work to set budgets for consortia.
'Variables... including the diagnoses of patients registered at each practice over two years... were used to predict the costs of providing care in the third year,' the report said. 'These weightings can now be applied to the most recent population data to determine a notional budget for each GP practice.'
The report said patients' details would be removed when used to calculate funding, and NHS numbers would be coded.
But Dr Holden said even if data is anonymised, patients' identity may be hard to hide if they have a rare condition.
Jon Ford, head of the BMA's health policy and economic research unit, said the Nuffield Trust's work could be used to allocate consortia budgets once an accurate formula is ready.
DoH national clinical commissioning network lead Dr James Kingsland has said the formula may not be ready until 2013 (GP, 17 September).