Patients who have low blood volume may experience inadequate blood flow to the kidney. A patient with high blood pressure and a decreased blood volume who is treated with a diuretic may develop a condition known as pre-renal azotemia. This is a form of kidney failure caused by inadequate blood flow. The blood tests to detect this problem are relatively insensitive and kidney damage may occur from inappropriate treatment. The current treatment for hypertension is a combination of vasodilators and diuretics.
Diuretics cause a decrease in blood volume in a patient.
In a patient with an increased blood volume diuretics are an ideal form of treatment, but in a patient with a decreased blood volume, diuretics may be harmful. The choice of medications for hypertension is usually a trial and error procedure because neither blood volume nor vasoconstriction is actually measured. With the use of a blood volume measurement, physicians would at least be in a position to have some understanding as to whether an expanded blood volume is a significant factor in the patient's high blood pressure. The physician would then be able to make a more precise choice of the appropriate therapy. Congestive heart failure is another relatively common condition where patients who are routinely treated with diuretics are sometimes over-treated resulting in complications.