Dog with heartworm has low blood platelets

[JulieCraig]

We adopted a beautiful American bull dog from a kill shelter. She had heartworm and is now being treated. We got blood tests done and her blood platelets came back a LOW 47k. They want to do an ultrasound first,  any way to tell another way why her count is so low? ? She's not lathorgic or weak or feverish, eats and drinks and wants to play but we are keeping her add calm as possible.
Any insight would help.  She is a year old American bull dog.
Thank you
Julie

[Margot49]

Ginger gave you good advice.  If she came from a shelter ask the Vet to test for Erlichiosis.  

[ginger899]

This could be Immune-Mediated Thrombocytopenia (IMT). It is an auto-immune response, where the dog's platelets are seen by the immune system as 'foreign matter', and attacked.
There are many triggers for this, but heartworm can be one of them.

There are medications to treat IMT, but they all may have side effects, and need careful monitoring by the vet.
If it is IMT then anything which further stimulates the immune system to any kind of response (such as booster vaccinations) will be under review, and it may be wise to withhold them (ask veterinary advice) The mandatory Rabies inoculations are not advised, and the vet can provide written confirmation for legal purposes.

You need to find out if it is IMT, so please do ask your vet about it.