Urine, a very complex fluid, is composed of 95% water and 5% solids .It is the end product of the metabolism carried out by billions of cells and results in an average urinary out put of 1-1.5 L per day.
Urine may also contain formed elements such as cells, casts, crystals, mucus and bacteria. Almost all substances found in urine are also find in the blood although in different concentration.
Specimen Collection:
-The specimen must be collected in a clean dry, disposable container.
– The container must be properly labeled with the patient name, date, and time of collection. The labels should be applied to the container and not to the lid.
– The specimen must be delivered to the laboratory on time and tested within1hr, specimen must be delivered within1hr, OR it should be Refrigerated or have an appropriate chemical preservative added. eg. Toluene, thymol, formalin or boric acid).
Types of specimens:
-Random specimen (at any time).
-First morning specimen.
-24 hr’s collection.
-Post. Prandial sample.
-Clear catch sample (midstream urine).
-Catheterized urine.
-Supra – pubic.
Physical examination of Urine (Macroscopic, Gross):—
1-Appearance (color and clarity):
A- color: Normal urine color has a wide range of variation ranging from pale yellow, straw, light yellow, yellow, dark yellow amber due to urochrome pigment (it’s an end product of endogen metabolism), trace of urobilin and uroerythrin.
The color is affected by: –
-Concentration of urine.
-pH.
-Metabolic activity.
-Diet intake.
-Drugs may change urine color.
B- Clarity (Transparency).
Normal urine clear or transparent, any turbidity will indicate.
-WBCs (pus).
-RBCs.
-Epithelial cells.
-Bacteria.
-Casts.
-Crystals.
-Lymph.
-Semen.
2-Odor :
Fresh normal urine has a faint aromatic odor due to the presence of some volatile acids.
In some pathological conditions, certain metabolites may be produced to give a specific odor such as:
-Fruity odor is due to acetone in Diabetic urine
-Ammoniac odor urine standing long time
-Offensive odor Bacterial action of pus (UTI).
-Asparagus Mousy odor Phenylalanine (phenyl keto urea “PKU” ).
3-Volume :
Adult urine volume = 600 – 2500 ml /24hr.
Children urine volume = 200 – 400ml /24hr. (4ml / kg / hr).
-Which depends on:
-Water in take .
-External temperature.
-Mental and physical state.
-Intake of fluid and diuretics (Drugs, alcohol – tea).
Abnormalities in volume :–
-Oligouria: marked decrease in urine flow < 400 ml.
-Polyuria: Marked increase in urine flow > 2500 ml.
-Anuria: complete stoppage of urine flow.
-Nocturia: excessive urination during night.
4-Specific Gravity (Spg) :
Specific gravity (which is directly proportional to urine osmolality which measures solute concentration) measures urine density, or the ability of the kidney to concentrate or dilute the urine over that of plasma.
Specific gravity between 1.002 and 1.035 on a random sample should be considered normal if kidney function is normal.
-Low specific gravity
-Diabetes Insipidus.
-Glamerulonephritis
-Sever renal damage .
-Excessive water intake.
High specific gravity:–
-Diabetes mellitus.
-Nephrosis.
-Fever since urine is conc.
-Urine preservative substance.
-X ray contrast media.
-Measurement of spg:
1- Urinometer :
2-Reagent strip:
Which contain polyelectrolyte, when ions increase in urine, more acidic groups are released, the change in pH will take place which change the color of bromothymol blue indicator.
5- Ph :
One of the important functions of the kidneys is pH regulation, the glomerular filtrate of blood plasma is usually acidified by renal tubules and collecting ducts from a pH of 7.4 to about 6 in the final urine to keep blood pH about 7.4.
Hence, urine pH must vary to compensate for diet and products of metabolism, this function takes place in the distal convoluted tubule with the secretion of both H+ & NH3+ and reabsorption of bicarbonate ei.
In cases of alkalosis, urinary pH will be alkaline by stop H+ excretion.
Normal urine pH is (4.6 – 8.0) as average (6.0).
Clinical significance of pH–
-Determine the existence of metabolic acid base disorder
-Precipitation of crystals to from stone requires specific pH for each type. Hence, pH control may inhibit the formation of these stones by control diet.
-May indicate the presence of urinary tract infection caused by urea splitting organisms.
– Defects in renal tubular secretions and reabsorption of acid & base.
-Determination of unsatisfactory specimens.
-Even in abnormal conditions, urine pH mustn’t reach 9, if so or more this will indicate that urine is stand for along time & must be rejected.
-Test for pH :
-Reagent strip which has an indicator (methyl red – bromothymol blue indicator) or other indicators.
Alkaline urine is found in: –
Patient with alkalemia, UTI, diets high with citrus fruits or vegetables.
Acidic urine is found in:–
Patient with acidemia, starvation, dehydration, high diets with meat products.
