How Does Urine Osmolality Results Help In Clinical Diagnosis.

: Admin : 2022-03-07

What are the functions of kidneys?

Every organ system in living organisms is structured, designed to perform definite functions. Digestion, absorption and metabolism of food are controlled by the digestive system. Blood filled with oxygen and nutrition reaches different parts of the body through the circulatory system. The nervous system controls different voluntary and involuntary actions of the body.  The excretory system is responsible for the drainage of waste products from the body thereby keeping it free from toxins. Kidneys, ureters, urinary bladder and urethra are organs that form the urinary system. Each organ plays an important role in the filtration of blood to create urine as a byproduct which later gets drained out of the system.

The human body consumes nutrients from food, that is utilized in the form of energy for different physiological functions of the body. After consumption of food that the body requires for different life processes, waste products are left behind the intestines and in the blood.  Urea is a waste product formed when foods rich in protein are broken down in the body. Urea is carried through the blood to the kidneys. Kidney functions here to remove it as a waste product when it gets mixed with water and other waste products to form urine. Kidneys maintain acid-base balance and electrolytes within the body. It regulates blood pressure. Thus kidneys are the primary organs of the excretory system that filter toxic waste products from the body in the form of urine which is excreted via the urethral opening through ureters after getting stored for a brief period in the urinary bladder.

What is the composition of urine?

Urine is the excretory waste by-product formed from the metabolism of food and fluids, flows from kidneys to ureters and gets stored in the urinary bladder. It is yellow made up of liquid wastewater, salt, electrolytes like potassium, phosphorus and chemicals like urea and uric acid. The formation of urine begins in nephrons, which are the structural and functional units or cells present in the kidneys. There are about 1,000,000 nephrons in the kidneys that filter toxins and waste products.  The blood plasma gets filtered within each nephron of the kidneys. Essential nutrients, water, amino acids and glucose are reabsorbed into the bloodstream from plasma leaving the concentrated level of waste products. This solution consists of water, urea, amino acids, inorganic salts, creatinine, ammonia and pigmented products of blood breakdown giving pale yellow colour to this liquid called urine.

When kidneys function normally, about 0.6 to 2.6 litres of urine per person is produced per day. The normal pH level of urine ranges from 4.5 to 8. Specific gravity in a normal healthy individual varies from 1.005 to 1.025. Normal urine is devoid of ketones, proteins, RBCs, WBCs, blood, bilirubin and glucose. Over ninety-nine per cent of urine, solutes are formed of sixty-eight chemicals. These chemicals have concentrations of up to 10 mg/l or more. These are electrolytes in the form of potassium, sodium, calcium, magnesium and chloride. Nitrogenous chemicals like urea and creatinine are also present in urine with organic acids like uric acid and other organic compounds.  Vitamins and hormones constitute part of this chemical composition.

Urinary solids constitute between 24.8 to 37.1 g/kg, primarily made up of organic matter. It contains a large amount of nitrogen, phosphorus and potassium. Nitrogen content in urine is high, which make up more than fifty per cent of total organic acids. Calcium and other ions like ammonium, sulfates from amino acids and phosphates are also excreted through the urine. A healthy kidney filters the above components which are later excreted outside the body through the urinary system. In any pathological condition affecting kidneys, this composition alters. Urine analysis during laboratory investigation, directs a pathologist, a physician to understand and diagnose a diseased condition.

What is URINE OSMOLALITY?

The word OSMOLALITY means the concentration of particles dissolved in a fluid. It measures the concentration of a substance that is dissolved in the solvent. When the concentration of a substance is more inside the fluid, OSMOLALITY would be higher. Urine osmolality measures the number of dissolved particles per unit of water in the urine. The concentration of dissolved particles can be detected in the urine by means of an osmolality test. The compounds or components present in urine like chloride, glucose, potassium, sodium and urea can be evaluated and measured by a urine osmolality test. The electrolyte levels in the body can be concluded through a urine osmolality test. It is the marker test to understand kidney functions, the levels may vary or change during a pathological diseased state of kidneys.

The number of molecules found in one kilogram of water is measured by an osmometer that calculates urine osmolality. It helps to assess the concentrating or filtration ability of kidneys. The minimum urine osmolality is 30-50 mOsm/kg. The osmolar gap is the difference between the calculated value and the measured value.  An increase in water intake permits a large amount of water excretion from kidneys where higher readings of osmolality can be recorded in tests. A normal osmolality level within the body is maintained by regulation of water intake, filtration and excretion of fluids by normal physiological functions of the body. This balances the water level in the body.

How is URINE OSMOLALITY measured?

A urine osmolality test is advised by a doctor to diagnose kidney diseases, assess their functions, monitor drug treatment and check any conditions that might affect its levels.

Patients with abnormally high or low blood sodium levels, excessive thirst, urination, nausea, confusion, lethargy, seizures, dehydration and chronic diarrhoea are advised a urine osmolality test. The laboratory analysis with a high or low reading indicates kidney functions. Dehydration and metabolic syndromes affect urine osmolality.

A balanced diet has to be followed by the patient prior few days the test is scheduled. Fluid intake should be restricted twelve to fourteen hours before the test. A clean, clear sample of the patient's urine is collected for laboratory analysis. It may be a random urine sample or collected over a period of twenty-four hours. The unit of measuring urine osmolality is milliosmoles per kilogram of water. The normal range varies from 500—850 mOsm/kg. Any deviation in these readings, either low or high indicates a diseased condition in the body.

An increase in osmolality readings is observed in patients having congestive cardiac failure, dehydration, high, liver cirrhosis, glucose and in cases of acute kidney injury. Low urine osmolality is found in patients with excessive hydration or high levels of fluid intake, glomerulonephritis, kidney failure and renal tubular necrosis.

Urine osmolality levels are of potential clinical significance. The amount of solute concentration filtered by the kidneys determines the body's homeostasis. Certain toxic substances and diseases create an imbalance in intracellular and extracellular fluid volumes that determine or derange urine osmolality.

What does osmolality levels indicate?

When the human body excretes toxins, an osmolality test provides screening for the presence of low molecular weight harmful irritants present in the serum. The concentration of obnoxious toxic substances like ethylene glycol, propylene glycol, ethanol, methanol and the concentration of salicylates can be found through a urine osmolality test. Certain medication given to reverse cerebral coma such as mannitol affects the osmolality of urine. An osmolality test indicates if any of its toxic effects on kidneys is present, thereby analysing relevant treatment to prevent damage of kidneys.

A patient who is in a coma, and osmometry can provide the assessment of the degree of hydration. Similarly, in the case of kidney dysfunction, the concentration of substances present in the urine can help in the prognosis of renal failure. Osmometry tests help to monitor patients' fluid levels during renal dialysis. The sodium imbalance during hyper or hyponatremia determines total body water homeostasis.

When kidneys are healthy, performing normal physiological functions, it concentrates urine to an osmolality that is four times greater than serum. In a healthy state, osmoreceptors in the hypothalamus sense diffusion of water into or out of receptor cells caused by changes in serum osmolality levels. Hypothalamus directs the pituitary to increase or decrease levels of vasopressin from the posterior pituitary gland. Vasopressin release causes an increase in water reabsorption in the distal tubules and collecting ducts of kidneys. This reduces water loss, concentrates urine where every component of urine can be measured by calculating osmolality level. In patients who are dehydrated, vasopressin release causes water conservation and increases water concentration. An increase in fluid content in the body leads to overload or excess of water that decreases the release of vasopressin which causes diuresis.

Patients with kidney dysfunction or any pathology may suffer from polyuria or oliguria, whose nephrons are damaged to an extent that they may not be able to concentrate urine. Urine osmolality tends to fall below the normal range.

How does urine osmolality affect renal output in patients with chronic kidney disease?

Urine osmolality indicates the physiological function of the kidney that concentrate urine. Patients suffering from chronic kidney disease have low glomerular filtration capacity, which may increase toxic waste products in the body due to lack of normal formation or drainage of urine out of the body. Patients may require dialysis or renal transplant. The low range of urine osmolality indicates progressive kidney failure.

Patients with chronic kidney disease have damaged tubules, that fail to concentrate urine. A low urine osmolality cause destruction of nephrons present in kidneys that decline kidney functions causing an irreversible structural and functional pathological change. Studies have revealed that fluctuations in osmolality readings affect kidney functions eventually leading to chronic kidney disease and renal failure. Congestive cardiac failure with a high risk of mortality is observed in patients suffering from chronic kidney disease. 

How does urine osmolality results help in clinical diagnosis?

Kidneys are the major organs of the excretory system that balance acid-base balance within the body. When cells of kidneys become dysfunctional, it affects metabolism, health and normal function of every system of the body. Urine OSMOLALITY analysis is an important diagnostic test conducted by pathologists worldwide, to record kidney functions.

For patients having hypokalemia, there is a drift in potassium level excretion showing a higher level of its output in urine. In patients with chronic hyperkalemia, urine analyses show low excretion rates affecting sodium absorption within the glomerulus depicting a metabolic syndrome similar to hypertension. Urine osmolality of more than 250 mm/kg is observed in patients who have polyuria in patients with chronic diabetes mellitus.

Patients who have increased urine output with low osmolality are at high risk of chronic kidney disease causing kidney failure. Patients with polycystic kidney disease show regression in glomerular filtration rates. Such patients succumb to renal insufficiency, which has high urine volume but decreases in osmolality levels.

Diseases that affect the kidney, metabolism and heart alter urine output and its concentration. The purpose to evaluate urine osmolality is to interpret different clinical conditions.  The concentration of electrolytes and ions of potassium, sodium and chlorine in the urine osmolality analysis test determine acid-base balance within the body.

The results obtained through osmolality urine tests vary with age, gender, health history and method used for the test. A high or low osmolality level in every abnormal condition of the body helps the physician to determine the treatment protocol. An increase in water intake in chronic kidney disease, urinary tract infections or urolithiasis adversely affects osmolality levels. Kidneys excrete the water intake after a maximum concentrating capacity of 1400 mm/kg to a minimum of 40 mm/kg in normal water metabolism. Urinary water loss is related to kidney functions. Hence, kidney functions should be maintained to their utmost fundamental capacity.

A patient should maintain health by avoiding stressful activities or eating a normal balanced diet devoid of food rich in sugar and calories that trigger metabolic diseases like diabetes mellitus that may cause diabetic nephropathy. An increase in food intake that causes a high concentration of electrolytes should be restricted to maintain urine osmolality levels. Kidney stones that damage their functions should be treated as an emergency by medical or surgical approach.

Silent kidney stones also cause damage to the glomerular filtration capacity of kidneys. When such pathological diseased state is identified, they should be treated with timely medical intervention. A healthy individual can restore the normal functions of the kidneys by increasing water intake that enhances its functions. Hydration to a certain extent has treated several clinical conditions. The aim of every remedial method is to sustain urine osmolality.