Can someone have an angiogram if his or her platelet level is at 50?

Low limit. 50, 000 is an abnormal value and the lower limit for which an invasive test can be performed without increased risk of bleeding. At this level the value should be confirmed just before the exam to make sure it has not decreased further.
Yes. 50, 000 is usually listed as the cut off for an increase in risk of bleeding, so exactly 50, 000 would probably be ok. One must always weigh the risk of bleeding against the need for the test.