You could always borrow someone elses urine if its a urine test (someone thats clean) , store urine in your fridge till the visit let it site one counter till it reaches room tempature then use those chemical hand warming packs they sell in the hunting/sporting section of walmart to keep the urine warm during ur hostpital visit.

If it is a mouth swab , try not to smoke for 4 or 5 days before the test and you should be good to go.