Wednesday, December 12, 2012

Cystic Fibrosis Carrier Screening

In my last post Cystic Fibrosis Screening I described how Tay-Sachs had been nearly eradicated in Israel and America and did a rough calculation as to why it would be cost effective to run a similar program to screen for Cystic Fibrosis in Ireland.

In this post I am going to take a closer look at the figures involved to give more evidence that such a screening program is justified.

The Cystic Fibrosis approve of genetic carrier screening for those related to people with CF and their partners. Genetic Carrier Testing For Cystic Fibrosis. 'Carrier testing is limited to adults over the age of 16 where there is a family history of CF, or where a family member has been found to be a carrier of a CF mutation' says the lab that does the testing.

[in the UK] 'A disadvantage of cascade testing is that it will not identify the majority of carrier couples since more than 80% of affected infants are born in families without a prior history of the disease'. Testing relatives though useful only covers a small fraction of potential CF cases.

This screening of relatives is paid for out of public funds

"How much does the test cost? GP fees will apply for arranging the blood test but molecular genetic testing at NCMG and any genetic counselling you may have is a public service and therefore free of charge".

This means that CF Ireland and the health service are involved in and support CF carrier screening. This means some of the moral objections to public screening that might have existed are not present.

What would population wide screening cost? The cost of genetic screening has fallen amazingly fast. for example here is the cost of sequencing an entire genome compared to Moores law.

23andMe a private company has recently announced it will for $99 dollars. This test checks for over 200 genetic markers including some forms of cystic fibrosis. This is further confirmation that genetic screening is getting much cheaper fast and that its current cost is quite low at less than a tenth of the cost of a night in hospital.

The list price of sending a sample from every 16 year old to 23andMe each year would at present be $7.5 million. There are reasons you might not want a private company to do this but it gives a baseline cost. This $7.5 million is the lifetime cost of under 8 CF patients 'However, the lifetime medical cost of the care of a CF child in today’s dollars was estimated to be slightly >$1,000,000'. To be economical, at US prices, this screening would have to prevent 8 of the roughly 40 CF sufferers born a year. Other genetic disorders are also screened for this $99 cost including many of those listed here. None of these are as common as CF in Ireland but these other disorders should be included in a full cost benefit analysis of genetic screening for the Irish population.

This $100 dollar cost is slightly deceptive as once someone finds out they are a CF carrier there are several options available to them. These vary in cost. They can decide (or matchmakers can ensure) not to have children with another carrier. If they do decide to have children with another carrier they can use IVF techniques to ensure an embryo without CF is implanted. Many of the cost analysis of CF screening (like the Rowley et al paper) include the possibility of screening a fetus for CF and terminating the pregnancy if found. This option is not legal in Ireland. They can ignore their and their partners screening results and have a baby as normal with all the risks that entails.

These costs and the probabilities on each have been worked out for the US in the 1998 paper Prenatal screening for cystic fibrosis carriers: an economic evaluation. 'the marginal cost for prenatal CF carrier screening is estimated to be $8,290 per quality-adjusted life-year. This value compares favorably with that of many accepted medical services. The cost of prenatal CF carrier screening could fall to equal the averted costs of CF patient care if the cost of carrier testing were to fall to $100'. This QALY cost figure is used by health care economists to decide which treatments and screenings meet a cost benefit analysis. The wikipedia page on QALY describes the measue well. According to this paper screening in the US, where CF is about four times rarer, is cost effective for the general population at current screening prices.

The paper 'Economic evaluation of cystic ļ¬brosis screening: A review of the literature' has further figures on the cost of screening. This paper is from 2008 and the figures it quotes can be from years before then. As an example of how much screening costs have dropped in that time 23andMe screening cost $999 in 2007 and is now $99 and screens for more genetic markers.

In the UK £30,000 per QALY is generally considered cost effective.

In Ireland what is the cost for a QALY? 'In Ireland, there is no fixed and generally agreed cost effectiveness threshold below which health care technologies would be considered by policy makers to be cost effective'. ’Pee-in-a-pot’ screening in third level institution/college settings may be considered cost effective if a cost effectiveness threshold in the region of €45,000 per QALY gained is used. This €45,000 per QALY gained seems to be a generally accepted figure.

There are more costs to screening than can be supped up in a € per QALY figure. Any screening will induce worry for example. Prostate, breast cancer and other screenings all also induce extra human costs not measurable in QALY though. These common screenings also have to meet these cost per QALY standards.

Given the US analysis at $8,290, screening costs having dropped drastically since then and the high rate of CF gene in the Irish population this implies to me full CF screening of the Irish population would be very cost effective.

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