To see how slow moving your gut is naturally on a daily basis you need to not take any stimulants like ducolax, senna or other before your sitz test so they can see how slow your gut is. Of course you will risk having a blockage. Of course first Ask you Dr what she wants you to do. Your guess is as good as mine about the blood test to see how your blood clots? Like pt and ptt, lft’s? Maybe she thinks your an alcoholic and its affecting your liver thus affecting your clotting factors????? Do you drink? Even if you do I don't see the relation with constipation or bleeding? Maybe you told her something you didnt say here on mayo. I guess alcohol could slow the gut down. A sitz study is just swallowing a pill that you will eventually pass, way longer than the average person. It’s not invasive. I had a sitz study and I didn't have to have any blood test. My blood test are perfect. Always ask for explanations? Always question. After I had a bad sitz test meaning the pill barely moved by the last x ray, I was started on linzess 290 daily. I also take miralax and magnesium every night at 7:30 pm. Linzess at 5 am on the dot! Let me know why the blood test and how your sitz test goes.