| Dave,
In 25 years of practice, I have never even heard of anyone trying to up their circulating volume with water prior ot a blood draw to supposedly make it easier to obatin a blood sample. For the average healthy person who is having routine blood work done in the doc's office, this is not necessary. There are any number of people who are a hard stick, no matter what their level of hydration. Cholesterol is not affected by dilution as stated above. Some of the other elements of the blood are, such as red cells, sodium and blood urea nitrogen. In a person with healthy kidneys, adrenal glands and endocrine response, the water bolus you drink will be dealt with as an increased urine output to your bladder. The body has a number of monitoring and response systems to maintain a proper fluid balance and blood volume. Since it is quite common for people to have a large battery of blood tests at one time, therefore necessitating only one stick, there are other lab tests being done that could be affected by a dilutional state, such as the tests I described above. It would take a good chunk of water to do this....like a liter or two about a half hour before before drawing. Unless you are a hard stick due to being dehydrated (and it taked more than 12 hours of fasting to do this....if you are not taking in fluid, the body will conserve water and urine output will decrease....there is no reason to drink a bunch of water before a blood draw and several reasons for not doing it. There are people who are a difficult stick....ie, the elderly, those on big doses of diuretics, the chronically ill, people who been having alot of sticks for things like chemo, morbid obesity, bigtime steroid users and those who simply have difficult veins. If you have had a problem in the past with venous access, it woudl best to ask your MD about fluid loading prior to a blood draw. I would suspect in most cases, the doc would tell you not to do it. |