A urine sodium test is used to test whether you are properly hydrated. It can also evaluate your kidney function.
There are two types of sodium urine test. A random test looks at sodium in a single urine sample. A 24-hour test looks at urine sodium over the course of a whole day.
Sodium is a mineral used in every cell of your body. It is especially important for the function of your nerves and muscles. It is also referred to as natrium or Na+.
The amount of sodium in your urine can help your doctor look for sodium imbalances in your body. It can be used to further understand abnormal values on an electrolyte blood test for sodium. It can help determine if your kidneys are working properly. Finally, this test can be used to test whether you are drinking an insufficient or excessive amount of water.
Your doctor may also order this test if you are suspected to have:
- hypertension: high blood pressure
- prerenal azotemia: high levels of nitrogen waste in the blood
- glomerulonephritis: a type of inflammatory kidney damage
- hepatorenal syndrome: kidney failure with liver cirrhosis
- medullary cystic kidney disease (MCKD): a genetic disease of cysts in the kidneys
- acute tubular necrosis: a type of kidney damage where the tubules of the kidneys are damaged or dying
Adults and older children can collect the sample for a random urine test easily. All it requires is urinating in a sterile plastic container at the medical facility. For an infant, urine is collected using a special bag placed inside the diaper. Your pediatrician will give you instructions for how to use the bag.
Collecting urine for a 24-hour urine sodium test is a bit more complicated. The collection process occurs at home. You will be given a special container to hold urine. Over the course of 24 hours, you will urinate into the special container. Typically, this is done over two days. On the first day, do not collect the first urine after you wake up. After that, urinate into the container every time. Stop after your first morning urination on the second day. The container should be delivered to your doctor or laboratory as soon as possible.
Before this test, you may need to stop taking certain drugs that affect sodium in the urine. These include:
- certain antibiotics (streptomycin, neomycin, etc.)
- diuretics (furosemide, HCTZ, etc.)
- corticosteroids (prednisone, cortisone, etc.)
- nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen, naproxen)
Tell your doctor about all over-the-counter and prescription drugs you take. Your doctor will say which you should discontinue. Do not stop taking medications unless you are told to do so.
Sodium in the diet may affect this test. A 24-hour test may be ordered to reduce the impact of any single meal.
A normal value for the 24-hour test depends on your dietary intake of salt and water. However, it is approximately 40 milliequivalents per liter per day (mEq/L/d). Some laboratories may have different maximum and minimum values.
There is no set normal for the random urine sample. It is too dependent on what you ate or drank in the hours before the test. In addition, the amount of sodium you excrete varies a lot. It is five times higher during the day than at night.
Low levels of sodium in your urine may indicate kidney problems or hyponatremia.
Hyponatremia means you have low levels of sodium in your blood. Symptoms include:
- nausea and vomiting
- loss of appetite
- confusion or disorientation
- loss of consciousness or coma
The causes of low sodium in the urine are most likely:
- excessive sweating
- kidney damage (e.g. glomerulonephritis, hepatorenal syndrome, or kidney failure)
- cirrhosis of the liver
- high levels of the hormone aldosterone
- congestive heart failure
High levels of sodium in the urine may be due to diet, kidney problems, or hypernatremia.
Hypernatremia means you have high levels of sodium in your blood. Symptoms include:
- swelling in hands and feet
- rapid heartbeat
The causes of high sodium in the urine may be:
- high-sodium diet
- certain medications (e.g. diuretics)
- problems with adrenal gland function
- salt-losing nephropathy (Bartter syndrome)