Urine analysis or urinalysis is the test of urine. It is used to detect and manage a wide range of disorders. Routine urine analysis comprises of three main examinations: Physical, Chemical and Biological examination. This article is solely based on physical examination of urine and their procedures, further upcoming articles will be focused on chemical as well as biological examinations of urine.
Urine is a fluid excreted by the kidneys, stored in the bladder and discharged through the urethra. Urine is a very complex fluid and is composed of 95% of water and 5% of solids.
Why Urine Analysis is needed?
Urine analysis is an essential procedure and one of the most useful indicator of health and disease, and it is especially useful in the detection of renal or metabolic disorders. It is aid in diagnosing and following the course of treatment in diseases of kidney and urinary system. Urine analysis also helps in detecting endocrine abnormalities in which the kidney function normally.
Instruction given to the patients before Urine analysis:
The patient should be instructed to void directly into the container. During the collection, the initial portion of urine stream is allowed to pass while the midstream portion is collected.
Preservation of Urine Sample:
All the specimen for urine analysis should be examined while fresh, when urine is kept for longer than one hour at room temperature various changes may occur such as:
- Breakdown of Red Blood Cells (RBCs) by hypotonic urine
- Decomposition of casts
- Bacterial multiplication
- Decrease in glucose level due to bacterial growth
- Formation of ammonia from urea by the action of bacteria
Chemical Preservatives used in Urine analysis:
Toluene, Formalin, Thymol, Chloroform, Commercial preservative tablets (contains formaldehyde).
Routine Urine analysis contains three main examination namely: Physical, Chemical and Microscopic examination.
Physical Examination of Urine:
Physical examination of urine comprises of total seven tests.
|No.||Physical Examination||Normal Values|
|1.||Volume||20ml (500 – 2000ml/day)|
|2.||Colour||Pale yellow to dark amber|
|4.||Sediment formation||No sediment formation|
|6.||pH||4.6 – 8.0|
|7.||Specific gravity||1.003 – 1.030|
For adult, the normal average daily volume of urine as about 500-2000ml/day. More urine formation takes place during the day than a night.
- Polyuria (>2000ml/day): Polyuria is an abnormal increase in the output of urine. It is generally observed in diabetes mellitus and diabetes insipidus.
- Oliguria (<500ml/day): Oliguria is a decrease urinary output than normal level. It can be due to dehydration or medicinal side effects.
- Anuria (<100ml/day): Anuria is the complete suppression of urine formation in spite of high fluid intake.
Freshly voided urine is transferred into clean, well dried measuring cylinder and the volume is measured.
The colour of normal urine may vary from pale yellow to dark yellow (amber), depending on the concentration of pigment “Urochrome” and also due to the presence of Urobilin and Uroerythin. Change in colour of urine also depends on diet, medicine and various chemicals.
|1.||Colourless or very pale||Dilute urine (diabetes mellitus and diabetes insipidus)|
|2.||Red||Haematuria, Hemoglobinuria, Myoglobinuria|
|3.||Dark brown or black||Alkaptonuria, Melanoma|
|6.||Yellow-green or green||Biliverdin|
|7.||Deep yellow with yellow foam||Bilirubin|
|9.||Orange or orange-brown||Urobilinogen|
|10.||Cloudy-white||Bacterial load or high WBCs|
|11.||Red or orange fluorescence with UV light||Porphyria|
Take freshly voided urine in glass test tube and observe the colour of urine. For more clear result, compare it with the colour of normal urine.
Normal urine is usually clear, but in some abnormal cases the urine may appear cloudy and hazy.
|1.||Cloudy||Presence of amorphous phosphates or amorphous urates|
|2.||Cloudy or turbid||Presence of leucocytes or epithelial cells|
|3.||Little cloudiness||Presence of bacteria|
|4.||Milky||Presence of mucus|
|5.||Hazy||Presence of fat and chyle|
|6.||Smoky and turbid||Presence of RBCs|
Take a urine sample in a clear glass test tube and carefully observe the appearance of it.
4. Sediment Formation
If the urine contains amorphous phosphates, amorphous urates, large numbers of leucocytes, epithelial cells etc. then it will form the sediment at the bottom of tube on leaving it for some time in same upright position.
Pour a fresh urine sample in the test tube and let it stand for about 10-15 minutes. Observe at the bottom of tube for the sediment formation.
The smell of freshly voided urine is generally aromatic, but in some condition the smell may vary.
|1.||Fruity or sweet smell||Presence of ketone bodies|
|2.||Pungent smell||Contamination of urine with urine (formation of ammonia)|
|3.||Musty odour||Urine of infact with phenyl ketonuria|
6. Reaction and pH
The freshly voided normal urine is usually slightly acidic and its pH may range from 4.6-7.0. Post prandial urine becomes less acidic or slightly alkaline due to the excretion of acid into the stomach after eating.
|Acidic Urine||Alkaline Urine|
|High protein intake||Diet with more vegetables|
|Ingestion of acidic fruits||Ingestion of citrus fruits|
|Respiratory acidosis (retention of carbon dioxide)||Respiratory alkalosis (hypertension)|
|Metabolic acidosis (in diabetic ketosis, severe diarrhoea, starvation, uraemina etc.)||Metabolic alkalosis (excessive vomiting)|
|UTI caused Escherichia coli||UTI caused by Proteus vulgaris and Pseudomonas aeruginosa (urea splitting bacteria)|
By using pasture pipette place a drop of urine on a pH paper and you can directly dip a pH paper or litmus paper in the tube containing urine. Rapid urine diagnostic dipsticks can also be used. Note the colour change and compare it with the standard colour chart given.
7. Specific gravity
Specific gravity at a constant temperature is the ratio of the weight of a volume of urine to the weight of same volume of distilled water.
The specific gravity is also known as relative mass density. SG determination is used to measure the concentrating and diluting power of kidneys. The specific gravity of normal urine is between 1.003 – 1.030. Usually the specific gravity raises when the fluid intake is low, and decrease when the fluid intake is high. The specific gravity of urine thus varies throughout the day.
- Hypersthenuria: The term used for the urine with high specific gravity (>1.030). Hypersthenuria is generally observed in diabetes mellitus due to the presence of glucose in urine.
- Isosthenuria: The term is used for the urine with fixed specific gravity of 1.010 which indicates poor tubular reabsorption.
- Hyposthenuria: The term is used for the urine with constantly low specific gravity (<1.003). The condition in which this problem occurs are pyelonephritis, hypertension, diabetes insipidus and protein malnutrition. Diuretic medicines and the natural diuretics such as alcohol and coffee can also cause hyposthenuria.
There are total three methods through which SG of urine is measured, they are as follows:
- Urinometer method
- Refractometer method, and
- Reagent strip method
This method works on the principle of buoyancy (i.e. the ability of a fluid to exert an upward thrust on a body place din it). When solute concentration is high, up thrust of solution increases and urinometer is pushed up (high SG). If solute concentration is low, urinometer sinks further into the urine (low SG).
The urinometer also known as hydrometer is placed in a container filled with urine. The urinometer is specifically calibrated in such a way that it sinks in distilled water up to the “0” mark. Thus the SG of distilled water is indicated as 1.000.
- Fill the measuring cylinder with 50ml of urine. If the quantity of urine is small, dilute the urine about 1:5 or 1:10.
- Remove all the foam by using filter paper.
- Lower the urinometer gently into the urine and let it float freely.
- Let urinometer settle, it should not touch the sides or bottom of the cylinder.
- Take the reading of SG on the scale (lowest point of meniscus) at the surface of the urine.
In case of diluted urine, multiply the last two numbers of recorded SG by dilution factor (5 or 10) and get corrected SG.
SG can be precisely determined by a refractometer, which measures the refractive index of the total soluble solids. Higher the concentration of total dissolved solids, higher the refractive index. Extent of refraction of a beam of light passed through urine and it is the measure of solute concentration, and thus of SG.
- With the help of pasture pipette place 1-2 drops of urine on the sample glass of refractometer by lifting the lid.
- Place the glass lid above the sample and the device process.
- Note the result from a scale by viewing through the lens or hole given or from digital display.
Reagent strip method
Reagent strip measures the concentration of ions in urine, which correlates with SG. Depending on the ionic strength of urine, a polyelectrolyte will ionize in proportion. This causes a change in colour of pH indicator (bromothymol blue).
- Remove the reagent strip from the box and dip it in the urine specimen.
- Note the colour change and compare the colour with standard colour chart given on the box.
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For chemical examination of urine/Determination of urinary protein