I have been smoke free for 28 days. have a blood test due for cotinine in 2 days. lets say it is very sensitive - would i test positive?

Unlikely: Cotinine should be out of your system long before now. Now that you have stopped using tobacco, stay away from it. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form. Practice safe sex, if you have sex. Get HPV vaccine

Mostly likely NEG: “When someone stops using tobacco & nicotine products, it can take more than 2 weeks for the blood level of cotinine to drop to the level that a non-tobacco user would have & several weeks more for the urine level to decrease to a very low concentration.” REF: http://labtestsonline.org/understanding/analytes/nicotine/tab/test/