Can fasting for a blood test cause low potassium?

No. Potassium levels are tightly regulated in the body. Fasting should not cause significant change in levels.
No. An overnight fast should not cause low potassium. See this site for more info on the subject.

Related Questions

I have low potassium and take supplements for it, but should I still get a blood test done? And would I have to stop taking them if I did?

Low potassium. You low potassium (k) is a problem. You're vomiting, that will cause a low k. You do not list that you are taking any diuretics that would lose both k and magnesium (m). Patients with m deficits have low k levels that cannot be corrected until their m is normal. There are renal losses of k that could give you a low k blood level. See you physician and find out why you are vomiting ; check k and m. Read more...

My doctor did a stress test and told me I had wolff parkinson syndrome. Blood test which showed low potassium. Could this be the problem not wps?

No. Wpw is a very specific electrical abnormality of the heart in which there is an extra electrical pathway, resulting in a unique ECG appearance. It may be associated with rapid heart rates we call re-entrant tachycardia. It is not caused by a low potassium. Read more...