Introduction
The concentration of all the particles in a fluid is called osmolality. For instance, the osmolality of thick sugar syrup will be higher than that of a cup of water with a pinch of sugar. This theory can be used in the human body to diagnose diseases. Osmolality is a diagnostic procedure used to analyze the concentration of chemicals like glucose, potassium, sodium, chloride, and urea in the given blood or urine sample. This is determined by the balance between water and other dissolved particles in a blood and urine sample. Two types of osmolality tests are usually done as diagnostic tests. These can include urine osmolality test and serum osmolality test.
What Is Osmolality Urine Test?
The osmolality urine test shows the number of dissolved particles in a unit of water in the urine. Since it measures urine concentration, it is more accurate than a specific gravity test. It helps assess disorders like diabetes insipid and determine the hydration status in the body. Any disorder involving antidiuretic hormone (ADH) requires both serum and urine osmolality to determine the kidney's concentrating ability.
What Is the Normal Urine Osmolality Rate?
The unit for urine osmolality is milliosmoles per kilogram of water (mOsm/kg). The normal urine osmolality is as the following:
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After 12- to 14-hour fluid restriction: >850 mOsm/kg H 2O (SI units).
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Random specimen: 50-1200 mOsm/kg H 2O, depending on fluid intake, or 50-1200 mmol/kg (SI units).
Why Is a Urine Osmolality Test Done?
A urine osmolality test can be done to check the body's water content or hydration status. It can be a measure of the ability of the body to produce urine. A urine osmolality test can be suggested in the following scenarios;
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An abnormally high or low blood sodium level.
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Excessive urination.
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Excessive thirst.
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Confusion.
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Fatigue without an explainable reason.
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Nausea.
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Lethargy.
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Seizure.
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Coma.
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Dehydration.
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Chronic diarrhea.
It is used to;
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Assess the functioning of the kidneys.
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Helps to decide if the electrolyte balance is normal.
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Monitor drug treatment.
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To check the effect of a treatment for any condition that would affect normal body osmolality.
How Is Urine Osmolality Test Done?
Before the test date, always follow a healthy and balanced diet. Sometimes, patients are advised to restrict their fluid intake about twelve to twenty-four hours before the test. Some medications like dextran or sucrose can interfere with the test results. Hence, it is essential to inform the healthcare professional of any medications taken. Other tests that involve consuming contrast dyes that can interfere with the test results should be avoided or informed to the healthcare provider.
Clean catch urine is required for the test. Clean catch urine is an uncontaminated sample. This includes collecting the sample during the middle of urination. A woman needs to clean her labia and urethra before the procedure. On the other hand, a man requires to clean the head of his penis before urinating. The patient is advised to collect the middle frame of urination.
What Does an Abnormal Urine Osmolality Test Signify?
A person with a normal diet and fluid intake can have a urine osmolality between 500 to 850mOsm/kg. While the excess fluid is consumed, a healthy kidney can concentrate urine to 800-1,400 mOsm/kg of water. On the other hand, in a dehydrated person, the osmolality value exceeds the plasma osmolality three to fourfold.
An increased urine osmolality value can indicate the following;
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Dehydration: The urine osmolality value increases in the case of dehydration. Dehydration can be due to decreased fluid intake, diarrhea, or vomiting.
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Syndrome of Inappropriate Antidiuretic Hormone Secretion(SIADH): It is a condition where the body produces more antidiuretic hormone. Antidiuretic hormone is a hormone that controls the amount of water lost by the body through urine.
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Adrenal Insufficiency: This is a condition where the adrenal gland cannot produce enough certain hormones. These hormones can include cortisol or a stress hormone.
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Glycosuria: The presence of sugars (like glucose, galactose, fructose, etc.) in urine is termed glycosuria.
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Hypernatremia: An elevated sodium level in blood is termed hypernatremia. It can be due to excess salt consumption or decreased fluid intake.
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Hyperglycemia: It is a condition where the blood glucose level is high. This happens when the body has very little insulin produced or is not able to use the insulin produced.
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Protein-rich Diet: A diet that is rich in protein can cause an increase in the urine osmolality value.
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Addison's Disease: A rare condition in which the adrenal glands cannot produce enough hormones. These hormones can include cortisol or aldosterone.
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Renal Artery Stenosis: The narrowing of the renal artery can affect the transport of fluids to and from the kidney.
A decreased urine osmolality value can indicate the following;
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Diabetes Insipidus: It is a rare disorder where the body produces too much urine. It is characterized by excessive thirst and heavy urination.
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Excessive Intake of Fluids: The urine osmolality test can give a decreased result when fluid consumption is more than what is needed for the body.
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Acute Renal Insufficiency: A condition where the kidneys cannot properly filter wastes from the body. As a result, a lot of waste accumulates in the body, causing a chemical imbalance. Proteinuria (the presence of protein in the urine) is the earliest sign of acute renal insufficiency.
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Glomerulonephritis: When the filters in the kidney become damaged, it is termed glomerulonephritis.
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Kidney Failure: It is a condition where one or both kidneys do not function independently. In other words, the kidneys cannot filter wastes properly or balance fluids.
Conclusion
The number of solutes present in a liquid is considered the osmolality of the liquid. It is used as a diagnostic tool for medical conditions. Many chemical molecules present in the urine can be used to measure osmolality. In a typical urine sample, the concentration of compounds like glucose, potassium, sodium, urea, and chloride can be taken into consideration.
