The problem is that it is difficult to know at what point a population becomes a high risk, medium or low risk group, particularly at the level of the GP.
b. Validation against the three Birmingham PCTs (2008 data) Because of the lack of local risk data at this point in time, the model currently uses national risk data as a default. Because Cardio-Vascular risk in Birmingham is generally higher than the national average, the model is currently under-predicting activity in this area. It is fairly easy to weight the populations in the model to adjust for this but no weighting formulae was available from the PCT at the time of writing this report. More accurate risk data will however be required in the future in-order to measure the impact of any interventions on mean risk. Fig 9
All acute CHD events - actual v predicted Birmingham PCTs 18000 16000 14000 12000 10000 8000 6000 4000 2000 0 16-24
25-24
35-44
45-54
Actual
55-64
55-74
75+
A ll events
Predicted
One of the problems we found with the application of the model in South Yorkshire was the tendency in the model to slightly over predict CKD activity. We have not adjusted for this yet because there is a known under-diagnosis of CKD in the UK, with the rates of dialysis being as low as 70 per 100,000 is some localities compared with 100 per 100,000 in Europe and 200 per 100,000 in the US. The introduction of electronic GFR reporting on routine blood tests introduced though the Renal National Service Framework is correcting this, but the full impact has not yet been felt in many areas. In addition, it is known that a proportion of kidney patients die of cardio-vascular related events before they reach dialysis. The model does not deduct this number at this stage. Again, the introduction of the care protocols within the Renal NSF will begin to reduce this number, bringing the actual number of events in the future nearer to the predicted number in the model. Finally, the actual events currently include only hospital-based dialysis patients. It is known that up to 20% of patients receive community-based dialysis in some areas. The CKD activity data from the Birmingham PCT’s related to episodes rather than patients. We have therefore simply assumed that predicted and actual activity would match for the purpose of validation at this stage.
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