I'm looking into health testing in yorkshire terriers. Is there anything I should be looking out for when buying a puppy.

There is some evidence of more than statistical average risk of liver shunt.

As with other small breeds luxating pattellas.

Neither condion has an official screening scheme.

There are clinical tests that parents can have.

You can improve your odds of finding a good healthy puppy, by contacting a known reputable breeder (best via the relevant Breed Club).   You should always be looking to finding a reputable breeder and never buy from an obvious BYB or a Pet Store (supplied by BYBs!!).   And if things don't feel right when you go visit any breeder, DON'T BUY.   Don't be conned into thinking you are 'rescuing' a puppy from such a home - easily done and I've been there, almost, when I switched my breed except I wasn't a novice and couldn't get out of the place fast enough.

Checking later, I don't see there are any KC/BVA Schemes available for this breed.

There are people who show this breed, even knowing there is a patella problem.  It isn't a KC requirement, but when I was breeding Yorkies it was something I liked testing for.  It's not a nice operation so best to try and breed this fault out. IMHO

Liver shunt definitely.  Yorkshire terriers are the breed most commonly affected with single congenital shunts. In fact, the risk of a Yorkshire terrier having a congenital shunt is 59 times greater than mixed breed dogs, and 36 times greater than all other breeds combined.  The problem is how could you know?  Blood tests can't be relied on until aged 16 weeks and even then that only indicates a liver shunt.  I don't know what you can do about this as even if both parents test Liver Shunt Free there is no test to determine a carrier.

Thank you everyone.

No health test will ever tell you that pups status will be, unless they are single gene specific DNA tests.

The incidence of Liver shunt may be statistically greater in the breed but it is still only 3% based on a US study.
http://www.ufaw.org.uk/dogs/yorkshire-terrier-portosystemic-shunt

"Number of animals affected

In the USA, around 3% of Yorkshire terriers have been found to be affected by portosystemic shunts (Tobias and Rohrbach 2003). As far as we are aware there are no data on prevalence in other countries."

"Genetics

The pattern of incidence of the disease (including the high prevalence in Yorkshire terriers) strongly suggests that it has a genetic cause, but the genes involved have not been determined. It is likely to be either an autosomal polygenetic condition or to be caused by a single gene with variable penetration (ie it is expressed in differing degrees in affected animals).

How do you know if an animal is a carrier or likely to become affected?

It is possible to test animals for PSS using a bile acid stimulation test. This can be done at a young age and before a puppy is sold by a breeder. There is no test to detect animals that may carry the harmful gene(s) without showing signs of the disease themselves."

The bile acid test is not reliable until 16 weeks of age unfortunately.  Pups have gone to their new homes long before this age.

If we put things i9n perspective Epilepsy occurs in the general canine population, mongrel pedigree whatever at about 1%, so your risk is 3 times that of having an epileptic dog.

As with Epilepsy al breeders can really do is avoiding repeating matings that have produced affected puppies and take care in doing similar pairing, and of course never breed from affected dogs.

All breeders can so is use what information is available to them and make breeding decisions hoping for the best.