Reasons and Symptoms Associated For Conducting a Blood Osmolality Test

Submitted on March 27, 2012

The number of solutes present in blood plasma can be assessed by using the osmolality test. The plasma, urine or stool is usually checked in this test. This test is generally prescribed to find out the water content of the body and its water balance. The presence of toxins in the body can also be assessed using this test.

Reasons To Conduct Osmolatity test

A serum osmolality test is usually prescribed to evaluate the following:

  • Water balance of body
  • Ability to process and concentrate urine and stool
  • Hyponatremia
  • Presence of harmful toxins that may have accumulated
  • Response of the body towards drug therapies with osmotically active drugs.

The blood plasma osmolarity is usually checked for an incidence of hyponatremia, a condition in which the concentration of salts in blood gets disturbed. Sodium, an important electrolyte in the body, loses its concentration in this disorder. When severe, this disorder can cause the brain to swell and have many other neurological effects.

Hyponatremia is usually a complication arising out of other medical conditions like diarrhea and vomiting in which the body's electrolyte balance is disturbed. Increased presence of proteins and lipids are also factors causing hyponatremia.

Usually, with blood plasma osmolarity, a urine osmolaltiy test is also prescribed. The test results of both blood and urine are together used to ascertain the water balance of the body. Excessive or decreased urination can be an indication of disturbed water balance in the body. Stool osmolaltiy on the other hand, is usually prescribed to evaluate diarrhea which is not caused due to any bacterial infections.

Symptoms Associated

Symptoms like excessive thirst, lethargy, nausea, confusion, coma and even seizures are usually associated with hyponatremia. In such a case, a urine osmolaltiy test is ordered to ascertain the presence of the disorder. Even to check for diabetes insipidus, osmolality test may be prescribed.

Interpretation of Test Results

A high blood osmolality is usually indicative of decreased water content in the blood. It may also signify an unprecedented increase of solutes in the blood plasma. Similarly if the result shows osmalility to be lower than normal blood osmolality, it is basically because the fluid and water level in the body is higher than the ideal level.

To check for blood osmolarity, human blood is collected with the help of a syringe. The doctors usually suggest the blood to be taken when the patient has not eaten anything for about 6 hour prior to the test. The normal result of the test is when the values range from 280-303 milli-osmoles per kilogram.