Osmolality (Urine)

The osmolality test is used to evaluate the dissolved particles in the urine. It calculates the dissolved sodium, potassium and urea in the urine to detect electrolyte imbalance.
Test Code: 460
₹ 1,200.00

Osmolality - Urine:

Why Osmolality Urine Test?


Osmolality is defined as the number of particles of solute per Kg of solvent expressed in osmoles (osm) i.e osmol/kg or Osm/kg. Osmolality can be measured on an analytical instrument called an osmometer (its principle is based on the depression of the freezing point). Osmolality in biochemistry (in the body) refers to the concentration of dissolved particles of chemicals and minerals such as electrolytes in the blood (serum) etc. Cell membranes are freely permeable to water. The osmolality of extra-cellular fluid (ECF) is almost equal to the intracellular fluid (ICF) concentration. Any change in the ECF osmolality will reflect on the osmolality of ICF. Therefore any alteration in the change in volume of water in ICF/ECF will affect the normal homeostasis and thus will reflect on the functioning of the normal cells. Osmolality is a test to measure fluid-to-particle balance in the biological fluid present in the body such as plasma (i.e plasma osmolality measures the body’s electrolyte-water balance) etc. Hence Osmolality test measures the number of certain substances (it includes glucose, urea, electrolytes – electrically charged minerals like sodium, potassium, chloride, bicarbonates etc) in the blood, urine and other biological sample specimens. Thus homeostasis is achieved in the body of healthy individuals. In certain pathologies kidney diseases, heart disease, poisoning (methanol, ethanol, ethylene glycol i.e anti-freeze, isopropyl alcohol – rubbing alcohol or antiseptic etc), small cell carcinoma of the lung, syndrome of inappropriate ADH secretion – SIADH, paraneoplastic syndrome etc, un-healthy fluid accumulation may be caused (eg. due to excessive salt intake etc).  Blood (serum or plasma) osmolality test is usually performed in conditions that include finding the balance between the water and other constituents in the blood, dehydration (to check the quantity of fluid loss in the body i.e to diagnose diabetes insipidus – when the kidney produces too much urine eg. caused due to ADH defect etc), over-hydration (how much excess water is retained – i.e edema), poisoning (to calculate the ingested amount of poison – eg methanol, ethanol, ethylene glycoli.e anti-freeze, isopropyl alcohol – rubbing alcohol or antiseptic etc). A urine Osmolality test is performed along with a blood sample. This test result is important in cases with increased or decreased urination etc.


Osmolality Urine test is performed to measure the concentration of particles in the urine. Greater than normal results reflects condition such as Addison’s disease, congestive heart failure or shock etc.

A stool osmolality test is performed in cases such as chronic diarrhea etc. Indicative clinical manifestations for osmolality test include signs and symptoms of altered levels of water intake, hiccups, dry cough, nausea, vomiting, headache, confusion, fatigue, seizure, shortness of breath, slurred speech etc. Abnormal osmolality results may indicate hypothyroidism, dehydration, over-hydration, heart failure, liver disease, kidney disease, excessive use of laxatives, mal-absorption, poisoning (methanol, ethanol, ethylene glycol i.e anti-freeze, isopropyl alcohol – rubbing alcohol or antiseptic etc), consumption of high or salts, Diabetes insipidus, stroke, small cell carcinoma of the lung, syndrome of inappropriate ADH secretion - SIADH, ectopic para-neoplastic syndrome (cancer) etc. Higher osmolality indicate the presence of more particles in the biological fluids eg. hyper-natremia, dehydration, diabetes insipidus (kidney produces too much urine), uremia, hyperglycemia, alcoholism, diabetic ketoacidosis etc. Lower osmolality indicate the presence of lesser particles in biological fluids i.e due to overhydration eg. hypo-natremia etc. Factors that may alter test results include altered quantities of water or fluid intake before test (hence 6 hours fasting i.e Nil Per Oral - NPO is necessary before this test), medications like diuretics (water pills), mannitol etc. Additional tests include CBC, glucose test, ADH Test, BUN, electrolyte panel, protein test, fecal occult blood test etc. 

General Instructions:

Sample RequirementSpecimen – Urine Sample. Test Preparation: None.

NOTE - Sample for specimen collections may vary based on the patient’s condition/cases according to the patient’s presenting complaints/signs or symptoms:

SPECIMEN REQUIREMENT (Special or Rare Cases) - As instructed and guided by Physician / Clinician / Pathologist / as per Laboratory’s requirements, according to procedures and protocols.

This Multi-Specialty Clinical Referral Laboratory RT DIAGNOSTICS provides precise and accurate tests with an extensive range of testing services to the medical centres to help in the diagnosis and identification of pathology in the test specimens for infectious diseases and also to evaluate the function of organ systems of the patient. It prevents further complications and helps to stabilize and restore health to near normalcy at the earliest without delay.