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Editors Selection IGR 8-2

Health economics: Costeffectiveness

Comment by Linus Jönsson on:

13939 Management of ocular hypertension: A cost-effectiveness approach from the Ocular Hypertension Treatment Study, Kymes SM; Kass MA; Anderson DR et al., American Journal of Ophthalmology, 2006; 141: 997-1008

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At what risk of developing POAG is it cost-effective to treat patients with ocular hypertension? Kymes et al. (608) address this issue in an economic analysis based on the Ocular Hypertension Treatment Study. A Markov-model was constructed with states for ocular hypertension, POAG in HAP stages 1-5, bilateral Health economics blindness and death. Costs, from a societal perspective, and utilities (values relating to quality of life) were assigned to each state based on US sources. Four strategies were examined: treating no-one before onset of POAG, treating patients with annual risk of developing POAG ≥ 5%, treating patients with annual risk ≥ 2% or treating everyone with IOP ≥ 24 mmHg.

Under base-case assumptions, treating all patients was not cost-effective compared to no treatment, with an incremental cost per quality-adjusted life years (QALY) of around US$145,000. Contrary to this, treating only patients with a ≥ 5% risk resulted in a cost per QALY of US$3670, while a risk of ≥ 2%, treatment was associated with a cost per quality-adjusted life-year (QALY) gained of US$42,430 compared to treating patients with ≥ 5% risk, and around US$29,000 compared to no treatment. This was judged as cost-effective by the authors, assuming a value of US$75,000-$100,000 per QALY.

Costeffectiveness data for treatment of patients with ocular hypertension provide important information for the management of glaucoma, provided assumptions on risk assessment in the individual patient are correct

• The definition of risk includes all patients above a certain level, e.g., all patients with a risk of e.g., 2% and more, and thus will not provide information about the cut-off levels. It is well possible that at 2%, treatment is not cost effective, as the ratios are highly influenced by those patients at a much higher risk. It might therefore have been interesting to look at a threshold analyses for given risks.
• The results of this model can only be applied to the United States, as data sources are US based. Although the clinical data are fully international, cost data, and to some extent, utility data are not. It should also be noted that there is no generally agreed threshold value per QALY and conventions vary between countries. For instance, the National Institute for Clinical Excellence (NICE) in the UK has stated an acceptable range of £20,000-£30,000 per QALY (US$37,000-US$56,000).
• Some of the information used in the model, such as the pro

  gression of POAG (HAP stages) or utilities are based on relatively limited data sets.

• Most importantly, however, the model assumes that the precise individual risk of a patient can be readily identified and does not take into account the uncertainty associated with determining this risk level. This is still a matter of scientific debate, and it is thus questionable whether such an assessment could currently be widely performed in the individual patient treatment setting. The cost-effectiveness of treatment depends entirely on this risk assessment, and the results of this analysis must be seen in this light.

However, the study illustrates nicely the crucial importance of targeting patients groups with the highest potential to benefit from treatment in order to optimize the use of health care resources.

Linus Jönsson is Managing Director European Health Economics, Stockholm, Sweden and has a PhD Health Economics from the Karolinksa Institute, Stockholm, Sweden

It is well known and unfortunate that compliance, adherence and persistence are far from ideal in the real world. The outcome of the OHTS is of course the ideal world. The authors could have modified their calculations and subsequently their conclusions based on a diminished effect of treatment due to the abovementioned issues.

When to treat is the topic of an ongoing discussion. As the authors mention the question is often whether to treat Ocular Hypertension or to wait for the earliest conversion. The current study does not address this question; it is however possible to carry out a cost-effectiveness study on that question. The experts in the field are encouraged to do so.

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