Understanding clinical risk scores in 4 days. Day 4: Treatment
Clinical trials tell us about the effects of certain drugs in certain patients in certain clinical situations. Arguably the most practical use of risk scores is to help in deciding which patients are most at risk of disease or have disease requiring most urgent treatment. In other words, risk scores can help answer the question, “Who needs treatment?”
An example we have used before is the CHADS2 score
for risk of stroke in patients with atrial fibrillation. Patients with a CHADS2 score of 2 or more should get warfarin therapy. Risk scores used in this way are easy to incorporate into treatment guidelines and are therefore translated into clinical practice fairly well.
However, we have already seen that risk scores are underused in clinical practice. In cardiovascular disease, to some extent, there are too many risk scores. These scores differ in terms of population, predictors and outcomes, which may not fit with those used by clinicians. Ideally, risk scores should be formulated, tried and tested in populations which have not received any treatment, but often patients in these populations have been treated, partially or fully and this is poorly accounted for by most rules.
Refining and re-defining of risk scores can lead to profound impact on who gets treatment, which can lead to a bigger impact on healthcare resources. For example, the CHADS2 system may not fully exclude risk of stroke in patients with a CHADS2 score of <2. Therefore, the CHA(2)DS(2)-VASc score was formulated to better define the patients with atrial fibrillation who truly are at low risk of stroke and therefore do not need warfarin. However, use of the CHA(2)DS(2)-VASc system does mean that more patients will go on warfarin treatment than with the CHADS2 system.
Another example is the impact of adding social deprivation to cardiovascular risk scores. One such score which incorporates the social gradient in cardiovascular disease is the ASSIGN score. Patients with an ASSIGN risk of 20% or more receive statin treatment. One study calculated that if the ASSIGN risk score was implemented, where a person lives would affect the decision to initiate statin treatment in the case of 15.7% of the population (aged 30-74 years), corresponding to 4.6 million in the UK.
The upshot is that risk scores are very versatile tools which can be used to guide diagnosis, prediction, prognosis and treatment in clinical practice, if the populations in which the scores were formulated and tested match your patient population, and you recognise their limitations.