Could diabetes or the presence of ketones in urine interfere with the results of a home pregnancy test?

Doubtful. Make sure the kit didn't expire. If you have ketones in your urine perhaps you should see a doctor anyway!
Blood test. If you have any doubt get a blood test for HCG to settle the issue.
Have a healthy diet, exercise, drink plenty of water, have safe sex, and get HPV vaccine. Wish you good health!
Nutrition: http://www.choosemyplate.gov/.
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