blood tests while on herceptin

Can anyone tell me what the blood tests are for while on herceptin treatment. I was told I will get tested every 4th cycle but not sure what for? Is this a check to see if the cancer has returned?

Hi Tara I have to have my blood tested every 3 weeks as I am on a trial (Herceptin and Pertuzemab). I was told that Herceptin can make your blood count drop slightly which is why they check it. I think also from my blood they check that my liver and kidneys are functioning ok. I don’t think it is to check if the cancer has returned so it’s nothing to worry about. Xx

Thank you Petal 123.