FAB PKD Screening Scheme

The FAB PKD Screening Scheme involves a panel of approved, highly-qualified veterinary ultrasonographers who will ultrasound scan the cat's kidneys looking for the presence of fluid-filled cysts. They will then issue an FAB-approved certificate stating the result of the scan for that particular cat.

To arrange to have your cat(s) examined under the FAB PKD Screening Scheme you will need to:-

1. Consult the list of FAB Approved Ultrasonographers to choose a suitable ultrasonographer.

2. Ask your vet to arrange a referral to an FAB approved ultrasonographer. Please download the referral letter for use by your vet.

3. Ensure that each cat has a microchip for identification. This can be done by your own vet, or it may be possible to have the microchip placed by the ultrasonographer. The microchip number will be checked by the ultrasonographer at the time of scanning; a certificate cannot be issued without a microchip number.

4. All cats examined under the scheme must be at least 10 months old.

A certificate will be issued by the ultrasonographer at the time of scanning. You will need to provide the following information:-

You will be given a copy of the certificate at the time of scanning. A copy of the certificate will be sent to your own vet and to the FAB and a copy will also be retained by the ultrasonographer.

In most cases cats can be scanned without the need for sedation. However, if the cat cannot be restrained adequately, then sedation may be required. We recommend that you do not feed your cat(s) before the scan in case sedation is required. If sedation is required this will involve an extra cost.

In most cases cats can be scanned without clipping the hair coat. However, the design of some ultrasound machines is such that clipping will always be required; the list of approved ultrasonographers indicates those centres that will need to clip the hair coat in every case. At other centres cats may need to be clipped if a clear image of each kidney cannot be obtained. A certificate will not be issued if it has not been possible to assess the kidneys fully.

The cost of the scan itself will be set by the ultrasonographer. The list of FAB Approved Ultrasonographers provides a guide to the fees charged by each ultrasonographer. There will be an additional administration fee of £4 per cat, or £3 per cat if more than four cats belonging to the same owner are scanned on the same day. You will need to provide a separate cheque, made payable to FAB to cover this administration fee.

Ultrasound scanning of cats over 10 months of age, by a highly skilled veterinary ultrasonographer, using a high-definition machine, has an accuracy rate of over 95 per cent.

An ultrasound probe, which emits high frequency energy waves, is placed against the cat's skin and is used to generate a black and white picture of the cat's internal organs. Ultrasound scanning is believed to be completely safe, and is not painful for the cat, but:-

Ultrasound waves are unable to pass through air, so a layer of gel is used to ensure good contact with the skin.

It is usually possible to get a good image of the kidney without needing to clip the hair, but in some cases this may be necessary in order to get a clear enough picture to identify very small cysts.

The cat must lie still for long enough for both kidneys to be thoroughly examined. Some cats may need to be lightly sedated in order to ensure that an accurate result is achieved, but this is rarely necessary.

All cats must be identified with a microchip before a certificate can be issued.

My local vets have an ultrasound scanner, why can't they scan my cat's kidneys ?

With appropriate expertise and equipment ultrasound scanning can be a very reliable indicator of the presence of cysts in the kidneys, but it is a very specialised task. If there are many large cysts they will be easy to recognise, but frequently the cysts will be tiny - less than 1mm in diameter. To identify these cysts a very high quality ultrasound machine is needed, and all of the kidney tissue must be thoroughly scrutinised. A cat cannot be said to be free of cysts unless the ultrasonographer can be confident that even the tiniest of cysts would have been seen if it was present.

When screening potential breeding stock for the presence of an inherited disease it is essential that the diagnostic test that is used is as accurate as possible. The FAB PKD Screening Scheme has been set up to achieve the highest possible standard of accuracy. An FAB PKD certificate provides a guarantee that the result recorded on the certificate is as accurate as it is possible to be.

Studies have indicated that once a cat has reached 10 months of age cysts can be identified with greater than 95 per cent accuracy. Below this age it may be possible to see cysts and hence to diagnose PKD, but at this young age if cysts are not seen then it doesn't mean that they aren't there.

Both the parents of my cat have been scanned and were negative. Do I still need to have my cat scanned ?

When two unaffected cats are mated all the resulting kittens will also be unaffected. However, while ultrasound scanning is currently the most reliable test for PKD, a small proportion of cats (less than 5%) may have cysts that cannot be seen. It is therefore recommended that ALL Persian and Exotic Shorthair cats are scanned before they are used for breeding, even if both parents have negative certificates.

You cannot advertise your cat as 'FAB PKD screened negative' unless a certificate has been issued for that cat.

The cost of the scan itself will be set by the ultrasonographer who performs the scan. A small additional charge will be made by the FAB, to cover the administrative costs of running the scheme. There is a reduction in price when more than four cats belonging to the same owner are scanned on the same day. A list of the approved ultrasonographers and their current prices is available on the website or from the FAB office.

In most cases each cat will only need to be scanned once, however very small cysts can be extremely difficult to see clearly on an ultrasound scan. If for any reason it is difficult for the ultrasonographer to be sure whether cysts are present or not they will record an 'equivocal' result on the certificate. These cats must be re-scanned after at least six months, by which time if cysts are present they may have grown sufficiently large to be clearly recognised. Equivocal results have been recorded for less than 2% of cats under the FAB scheme.

Ultrasound scanning under the FAB scheme is accurate in at least 95% of cases, however it is inevitable that errors will occasionally occur. These errors will usually come to light in the second generation, if a mating between two cats that were thought to be unaffected produces a kitten that is found to be affected by PKD. This is a very rare occurrence within the FAB Scheme (less than 1% of cats seen), but whenever it occurs the FAB is committed to investigating the source of the error. This will involve re-scanning the cats involved, which will be done at no cost to the owner(s) of the cats, but does require that owners and breeders co-operate as far as possible in making these cats available for re-examination.

Ultrasound scanning of pregnant cats is believed to be safe, but can only be carried out at the owner's risk.

My cat has been scanned under the FAB scheme and no kidney cysts have been seen. What does this mean ?

Ultrasound scanning of cats over 10 months of age, by a skilled ultrasonographer, using a high-definition machine, has an accuracy rate of over 95 per cent. So, if no cysts have been seen, you can assume that your cat does not have PKD and it therefore does not carry the PKD-gene and cannot pass PKD on to its kittens. If you mate this cat to another cat that does not have PKD then none of the kittens will be affected. If you mate this cat to a cat that does have PKD then you can expect that approximately half of their kittens will be affected with PKD.

The ultrasonographic appearance of a normal cat's kidney showing the dark central medulla region surrounded by the paler kidney cortex

A severely affected kidney. There are many circular black cysts of varying size throughout the kidney (arrows)

My cat has been scanned under the FAB scheme and kidney cysts have been seen. What does this mean ?

Cysts in the kidneys can occur for reasons other than PKD, but this is extremely rare, so if kidney cysts have been seen, you should assume that your cat does have PKD. This means that it carries the PKD-gene and can pass PKD on to its kittens. If you mate this cat to a cat that does not have PKD then you can expect that approximately half of their kittens will be affected with PKD. If you mate this cat to a cat that also has PKD then you can expect that around a quarter of their kittens will die before birth (because they will inherit two copies of the abnormal gene) and that of the remaining kittens around two thirds of them will be affected by PKD and only one third of them will be free of PKD.

My cat has been scanned under the FAB scheme but I was told that it was not possible to say whether there were cysts in its kidneys or not. What does this mean ?

Very small cysts can be extremely difficult to see clearly on an ultrasound scan, even when the scanning is done by an ultrasonographer who is highly skilled at examining cats' kidneys using a high definition ultrasound machine. It is very important that you are able to make an informed decision on your cat's breeding future and an inaccurate result would be extremely misleading. For this reason if it is difficult for the ultrasonographer to be sure whether cysts are present or not it is recommended that the cat should be re-scanned after at least six months, by which time if cysts are present they may have grown sufficiently large to be clearly recognised. It is also recommended that the cat is not used for breeding until it has been re-scanned and its PKD status has been clarified.

Studies indicate that under ideal conditions, ultrasound scanning for PKD gives a correct result in more than 95% of cases. The FAB PKD Screening Scheme is designed to ensure that the results of screening are as accurate as it is possible to be, but it is inevitable that a small number of errors will occur. These errors have usually been discovered because a mating between two cats that were thought to be unaffected has produced a kitten that is found to be affected by PKD. For this reason it is very important that ALL Persian and Exotic Shorthair cats are scanned for PKD before they are used for breeding, even if both parents have negative certificates.

If the predicted accuracy rate of 95% is achieved, then there will be 5 errors per 100 cats examined. In the first three years that the scheme has been in operation over 1500 cats have been screened and less than 1% of errors have been identified. The FAB is committed to investigating the source of all errors that occur within the scheme, and to re-examining all the cats involved, at no costs to their owner(s).

You may ask your veterinary surgeon to refer you to one of these approved ultrasonographers. You will not be able to make an appointment without a referral letter from your veterinary surgeon.

Veterinary ultrasonographers who fulfill the following requirements are eligible to join the FAB panel of approved ultrasonographers:-

•Holder of the RCVS Diploma in Veterinary Radiology, the diploma of the European College of Veterinary Diagnostic Imaging, or an internationally recognised equivalent qualification in diagnostic imaging.

•Access to an ultrasound machine with a transducer frequency of at least 7.5MHz.

Veterinary ultrasonographers who do not have a diploma in veterinary imaging, but who can demonstrate a depth of experience in ultrasonographic diagnosis of polycystic kidney disease in cats, are invited to apply in writing to the FAB for special approval.