Urinalysis: Collection, Preservation and Physical Examination

Introduction

Urine is an ultra-filtrate of plasma from which substances essential to the body are reabsorbed and through which those substances not needed are excreted. The nature and amount of substances present in urine reflect ongoing physiological processes in health and disease states.

Routine urine analysis is mainly performed for two purposes: 

• To find out the metabolic and endocrine disturbances of body
• To detect the intrinsic condition that may adversely affect the urinary tract or the kidney.

Collection of urine

For urine analysis fresh early morning sample is preferred because it is most concentrated and acidic which preserves the formed elements well. For the quantitative test and concentration test for tubercle bacilli 24 hour urine specimen is required. For bacteriological test collected urine sample should be free from contamination and it should be collected in sterile container .collection by catheterization into sterile container is the best.
Midstream urine is preferred. The specimen should be collected in a clean and dry container. The technician should instruct the patient properly. Before collecting the urine the male patient should clean the glands penis and the female should clean the vulva. The midstream urine should be collected and container should be closely capped. For 24 hour specimen the early morning urine specimen is discarded and all the urine during next 24 hour including the early morning urine the next day is collected.

Preservatives

The urine sample should be examined within 1 to 2 hours of collection in order to prevent from decomposition and contaminations in delay condition, in 24 hour urine specimen collection and in mailing of the specimen to the distant laboratory for examination sample should be preserved in preservatives

Varieties of preservatives used are

1. Toluene: 2ml/100ml of urine
2. Formalin: 3 drops for 100 ml of urine
3. Thymol: 1 small crystals/100ml of urine
4. Chloroform: 5ml/100ml of urine
5. HCl: 10ml in 24 hour urine specimen
6. Boric acid: 0.3gm in 120ml

Physical Examination of Urine

Volume

The normal average daily volume of urine in adult is about 1200-1500ml .more urine formation takes place during the day than the night. However the normal range for 24 hr may be 600-2000ml.

• Polyuria: increased execration of urine>25000.seen in diabetes mellitus and diabetes insipidus.
• Oliguria: decreased in 24 hour urinary excretion <500ml.
• Anuria: complete suppression of urine formation in spite of high fluid intake as in renal failure.

Color

The color of urine is due to the presence of urobilin and urochrome. Urochrome is produced due endogenous metabolic process. The intensity of yellow color may indicate urine concentration and client’s state of hydration. Dilute urine is pale in color which can be seen after the excessive fluid intake. It can be seen in diabetes mellitus patient due to the osmotic diuresis resulting from excessive glucose load. The concentrated urine is deep yellow in color due to presence of bilirubin.

Some of the examples of pathological changes in color are:

1. Milky white: Chyluria due to filariasis and UTI
2. Orange: Urobilinogenuria, fever, excessive swelling concentrated urine
3. Red: Hematuria, Hemoglobinuria, Myoglobunuria, Excess of  Vit B₂
4. Greenish: Poisoning, Jaundice
5. Greenish dirty blue: Cholera, Methylene blue
6. Brown yellow red: Acidic urine
7. Dark brown yellow red: Concentrated urine, bilirubin, acute febrile disease.
8. Bright red: Cascara (alkaline urine)
9. Black urine: UTI, Hemorrhage (acidic urine) hemoglobinuria, Alkaptonuria
10. Smoky brown: Blood pigments.

Odour

Normal fresh urine is slightly aromatic odour due to the decomposition of urea forming ammonia.

1. Fruity odour: Ketonuria due to the uncontrolled diabetes mellitus or starvation
2. Mousey: Phenylkutinuria
3. Maple syrup: Maple syrup urine disease.
4. Fishy or fetid: Acute renal failure due to the acute tubular necrosis and failure of normal mechanism of ammonium secretion. 

Appearance

Urine is normally clear or slightly cloudy. In alkaline urine cloudiness is due to the presence of amorphous phosphate and carbonates. In acidic urine cloudiness is due to presence of amorphous urates, uric acid and calcium oxalate.

Other substances that cause cloudiness are RBC & WBC, epithelial cells bacteria fungi. It can be get rid by centrifugation. Presence of these substances indicates inflammation or infection of genital or urinary tract. Mucus yeast sperm prostate fluid menstrual and vaginal discharge fecal material lymph and other external substances also cause cloudiness. Fat and chyle also causes turbidity due to the colloidal suspension of lipid which can be get rid by centrifugation.

Reaction

Normally 24 hour specimen of urine preserved without contamination is slightly acidic in nature with a pH of 6.0. This is due to presence of weak organic acids and acid phosphates. Normal range of urine pH ranges from pH 4.7 to 8.0.

• Acidic urine: a diet high in meat certain fruits such as cranberries. When hydrogen ions are secreted instead of potassium ions in order to maintain electrochemical neutrality in renal tubules, drugs ammonium chloride. Respiratory acidosis metabolic acidosis, UTI cause by E coli.
• Alkaline urine: a diet high in vegetables and citrus fruits.eg-respiratory alkalosis, excess vomiting urinary infection caused by Proteus, Pseudomonas, drugs sodium bicarbonate, potassium citrate, acetazolamide, on standing at room temperature.

Indicators  

• Blue to red-acidic
• Red to blue alkaline-alkaline.
• Blue and red to purple-neutral.

Specific Gravity

Fig. Urinometer

It gives an indication of the amount of solids in solution in the urine. The normal specific gravity of urine is between 1.015 to 1.025 in 24 hours specimens, but there are considerable variations in the reading in sample taken at different time interval of the day. The factors mentioned under volume influence the specific gravity taken at various time. Generally the greater the volume the lower is the specific gravity except in diabetes mellitus. The chief substances influencing the specific gravity of urine are urea, sodium chloride and phosphates .In severe renal diseases it may not be for the kidney to concentrate the urine and so the specific gravity is low.

Increased specific gravity is seen in diabetes mellitus, dehydration, eclampsia, protenuria, lipid necrosis etc. Excretion of urine of high specific gravity is called Hyperesthenuria. Excretion of urine of a fixed specific gravity of 1.010 indicates poor tubular reabsorption and called as Isosthenuria. Excretion of urine of consistently low specific gravity is called Hyposthenuria. The diseases which can cause this problem are pyelonephritis, hypertension, diabetes insipidus and protein malnutrition.

Procedure-

Observe the following aspects of urine specimen

Note the following things.

• Color
• Appearance
• Odour.
• Sediment.
• Specific gravity.  

Volume

Measure the volume of urine and note it down.

Reaction and PH

It is checked by using litmus paper. Place a drop of urine in litmus paper and observe the color change and note down the reaction and pH.

Specific gravity

It is measured by using Urinometer. It is a weighted cylinder that floats in the urine and has a scale in the stem with readings from 1.000 to 1.060 with division of 0.001-0.002.

For specific gravity determination,

1. Mix the urine well and fill 3/4^th of container with urine.
2. Remove all foam with the help of rough filter paper.
3. Float the urinometer in the urine .the urinometer shouldn’t touch the bottom or sides of container.
4. Note down the specific gravity.  

Note:

• The Urinometer is calibrated for certain temperature which is marked in it. The readings need to be corrected because urine like other fluids expands as the temperature rises thus lowering the specific gravity.
• Corrected specific gravity = Specific gravity measured at 15 degree centigrade + (Room Temperature-15 degree centigrade/3) X 0.001
• The specific gravity of urine can also be determined by falling drop and refractometer by using only few drops of urine.
• If the quantity of urine is small, dilute the urine, then multiply the last 2 numbers of the recorded specific gravity by dilution factor.
• Acidic urine helps to prevent the formation of ammonium magnesium kidney stones which are more likely to form alkaline urine
• Alkaline urine is used in the treatment of kanamycin in sulfonamide therapy and in the treatment of salicylate poisoning.
• On standing at room temperature the following changes take place in urine
• Lysis of RBC by hypotonic urine
• Decomposition of cast
• Bacterial multiplication
• Decrease in glucose level
• Formation of ammonia from urea by the action of bacteria.
• For urgent routine examination random specimen may be used however to get general idea of expected pathological condition.