Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Hyponatremia refers to a lower-than-normal level of sodium in the blood.
Sodium is essential for many body functions including the maintenance of fluid
balance, regulation of blood pressure, and normal function of the nervous
system. Hyponatremia has sometimes been referred to as "water intoxication,"
especially when it is due to the consumption of excess water, for example during
strenuous exercise, without adequate replacement of sodium.
Sodium is the major positively charged ion (cation) in the fluid outside of
cells of the body. The chemical notation for sodium is Na. When combined with
chloride (Cl), the
resulting substance is table salt (NaCl).
The normal blood sodium level is 135 - 145 milliEquivalents/liter (mEq/L), or
in international units, 135 - 145 millimoles/liter (mmol/L). Results may vary
slightly among different laboratories.
What causes hyponatremia (low blood sodium)?
A low sodium level in the blood may result from excess
water or fluid in the body, diluting the normal amount of sodium so that the
concentration appears low. This type of hyponatremia can be the result of
chronic conditions such as kidney failure (when excess fluid cannot be
efficiently excreted) and congestive heart failure, in which excess fluid
accumulates in the body. SIADH (syndrome of inappropriate anti-diuretic hormone)
is a disease whereby the body produces too much anti-diuretic hormone (ADH), resulting in retention of water in the body.
Consuming excess water, for example during strenuous exercise, without adequate
replacement of sodium, can also result in hyponatremia.
Hyponatremia can also result when sodium is lost from the body or when both
sodium and fluid are lost from the body, for example, during prolonged
sweating and severe
vomiting or diarrhea.
Medical conditions that can sometimes be associated with
hyponatremia are adrenal insufficiency, hypothyroidism, and
cirrhosis of the
Finally, a number of medications can lower blood sodium levels. Examples
of these include diuretics, vasopressin, and the sulfonylurea drugs.
Viewer Question: My trainer is always telling me to stay hydrated. How much water should I drink when exercising? What will happen if I drink too much?
Fitness Expert's Response: The National Athletic Trainers' Association recommends the following hydration guidelines for exercise:
Two to three hours pre-exercise: 17 to 20 fluid ounces of water or sports drink.
Ten to 20 minutes pre-exercise: 7 to 10 ounces of water or sports drink.
During exercise: Fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces of water or sports drink every 10 to 20 minutes.
A urinalysis is simply an analysis of the urine. It is a very common test that can be performed in many healthcare settings including doctors' offices, urgent care facilities, laboratories, and hospitals.