Health economics of Colonix: A new diagnostic test in colorectal cancer

The Colonix test is used for the early detection/screening of colorectal cancer and other bowel diseases such as inflammatory bowel disease (IBD). An economic model has been constructed to estimate the cost-effectiveness of the use of the Colonix device as a precolonoscopy evaluation test in a primary care setting, i.e. for patients presenting symptomatically to their GP. The aim of using Colonix as a pre-colonoscopy test would be to avoid unnecessary colonoscopies, as colonoscopy is costly, invasive and comes with a risk of perforation.

A cost effectiveness model was built in Treeage. The population consists of patients who have presented to their GP with distal colonic symptoms who were subsequently referred by their GP for endoscopic assessment. Essentially the Colonix test will help determine whether urgent colonoscopy or an extended observation period is preferable. The model calculates costs incurred and QALYs gained over a patient’s lifetime.

A life-time horizon was used as it is possible that a false negative test result could cause a delay in diagnosis which could compromise patient survival, thus affecting QALY gains over a patient's lifetime. The model includes diagnostic test costs and associated costs such as retests and treating bowel perforations due to colonoscopy and it includes colorectal cancer treatment costs. The model is populated with data relating to diagnostic test characteristics, disease prevalence, diagnostic test costs, CRC treatments costs, health state utility values and CRC natural history.

The model output includes the incremental cost effectiveness ratio (ICER), net monetary benefit (NMB) and number of colonoscopies avoided. The model structure allows all parameters such as Colonix test characteristics, cost of Colonix, etc to be easily updated. With the current model assumptions (e.g. patients receiving a true negative Colonix test incur no additional diagnosis costs) the use of Colonix is cost-effective at a willingness to pay of £20K and has a NMB of just over £200 per person. It will also result in around 60% fewer colonoscopies.

In constructing the model, the importance of correctly representing the treatment pathways became evident. Further information relating to the diagnostic pathways for patients receiving a negative Colonix result is required to correctly model the economics. Specifically sensitivity analyses showed that the model results are highly dependent on the variable "cost of additional diagnostics following a negative Colonix test". This cost will be different for patients with different underlying conditions and this should be reflected in the modelling. Three potential courses of action are suggested:

1) Collect further subjective clinical judgement relating to diagnostic pathways following a negative Colonix result.

2) Examine what information of patient pathways is obtainable from existing Colonix trials – i.e. what subsequent diagnostic tests patients received following a negative result.

3) Undertake a randomized control trial (RCT) to directly compare the two fully defined alternative diagnostic pathways (one pathway to represent the existing situation and one to include Colonix).