The nurse should obtain the specimen from the catheter.
One of the tests from urinalysis that frequently got contaminated is about infection. The area near the orificium of uretra is near the skin, so there will be microbes around it that can contaminate the sample. The contaminated sample will give a false positive and the result will show the urine are infected.
Taking the specimen from catheter will prevent that contamination, thus giving a better sample.
I believe you're talking about a population.
