An osmolality test measures the quantity of solutes present in the urine, stool or plasma. It can be ordered for several purposes such as evaluating the water balance of the body and, aiding in the investigation of hyponatremia., It aids in detecting toxins such as ethylene glycol and methanol and evaluating the urine production and concentration ability of the body. It may also be ordered to evaluate drug therapies that are osmotically active and to determine the effectiveness of treatments.
A plasma osmolality test may be ordered when the individual is experiencing symptoms such as nausea, headache, thirst, confusion, sluggishness, seizures and coma., which is These are suspected to be occur due to hyponatremia or due to ingestion of toxins. A urine osmolality test may be ordered in accompaniment with a plasma test when both results need to be compared and also when the individual’s urine production may have increased or decreased. Both osmolality tests may be ordered when the individual is suspected of having diabetes insipidus. Stool osmolality tests may be ordered when the individual is suspected of having chronic diarrhea possibly due to a substance that is osmotically active.
For the plasma osmolality test, a needle is inserted into a vein in the upper arm of the individual and a blood sample is obtained. For a urine osmolality test, a urine sample is obtained using the clean catch method. This involves collecting a sample of urine first thing in the morning when the urine is concentrated and therefore likely to allow detection of any abnormalities. The genital area must be cleaned before obtaining the sample as bacteria from the skin may cause contamination and affect the results. The individual must then begin to urinate, allowing some urine to pass into the toilet. Then he must collect a couple of ounces of urine in a sterile container, and pass the remaining into the toilet. For a stool osmolality test, a fresh sample of liquid stool that has not been contaminated by any urine is obtained. This sample is tested upon within half an hour after collection as the bacteria present may affect the results after a certain period of time.
If there is a greater concentration of an atypical substance such as protein, red blood cells or glucose, it is likely that there is a problem which must be addressed. Higher than normal levels may be indicative of dehydration, head trauma, hyperglycemia, and hypernatremia, among the other conditions.