Loose stool for kitten

I adopted my domestic shorthair around 2mths of age from the humane society. There, they gave her Pyrantel as the de-wormer and ask for a vet checkup within 2 weeks. I also have another kitten adopted from there, so I took him as well to their first appt. The vet gave both of them an oral, liquid de-wormer, checked their stools, and said they were OK. On their last visit, they got another round of the oral liquid de-wormer and a URI vaccination. On the next visit on June 4th, I am asked to bring another stool sample.
Ok with that background, here's the real problem. I clean the litter box once in the morning before work and once in the afternoon after work. For the past 3 days, I have noticed loosely formed stool (I'm pretty sure it's from my female) in the back of the box. Well yesterday morning, I noticed a streak of blood running the length of the stool. It wasn't bright, more of a crimson color and I could only notice it when inspecting the stool closely (looking for possible worm fragments). Both the kittens get Science Diet and have fresh water daily, along with one can of wet food a week.
Sooooo, what could be the cause of her loose and kind of bloody stool?

[Aleda M Cheng, D.V.M., C.V.A]

Blood in the stool can be due to parasites that are not covered by the liquid dewormer which is either Pyrantal or Strongid.  These anti-wormers do not cover tape worm, giardia or coccidia.  Giardia and Coccidia can cause blood in the stool.

Other causes of blood in the stool are anal gland infections, gastrointestinal disorders such as Inflammatory bowel disease, or food allergy gastroenteritis and other less common problems.  GI parasites are intermittently shed, so even if a stool sample is negative the patient can still have parasites.  Please call your vet about this and bring in a stool sample that contains the blood ASAP.

Lastly, all cats of any age should be on wet food primarily.   Use the dry food as no more than 1/4 of their diet or less.