1. Turbidimetric and chemical procedures: Provide an accurate estimation. Colorimetric readings taken against blanks and calculations done accordingly give the result (example; sulfosalicylic acid turbidity
alkaline urine or phenolphthalein and pyridium in
acid urine or deferoxamine can produce red urine
• Phenolphthalein in alkaline urine produces purple
• Phenylhydrazine and phenolic drugs produce dark
• Cascara may produce brown-black urine
• Riboflavin or pyridium in alkaline urine produce
• Levodopa causes urine to darken on standing
• Iron salt consumption produces dark colored urine
• Phenothiazine tranquilizers cause pink to brown
• Triamterene causes pale blue colored urine.
Average range: 4.6 to 8, Average pH = 6.0
Litmus paper or other pH indicator papers broad range
(pH 1 to 12) or narrow range pH papers can be used.
Another simple method is to add 2 drops of 0.4% alcoholic
solution of methyl red to 5 mL of urine. Note the color
change—if red = acidic; orange = neutral; yellow = alkaline.
Digital electronic pH meters for better accuracy can be
used—here, the electrode is dipped in urine and pH read
off directly from the digital display.
Amongst urinary tract infections, Escherichia coli
produce acidic urine, while Proteus (urea splitting)
produces alkaline urine. Meat protein diet causes urinary
acidification, while consumption of citrus fruits makes the
Ketosis Diabetes, starvation, febrile illness in children.
Acidification Used in treating urinary tract infections, and to
prevent precipitation of calcium carbonate or
phosphates or magnesium ammonium phosphate
Normal finding in specimens voided shortly after
Vegetarianism Meats produce fixed acid residue, vegetarian diet
Systemic As may occur in severe vomiting, hyperventilation, excess alkali ingestion
Urinary tract Proteus or Pseudomonas infection, they split
Alkalinization Used to prevent crystallization of uric acid,
oxalate, cystine, sulfonamides, streptomycin
Stale specimen Bacterial overgrowth. If true infection exists, the
sediment should show pus cells
¾ On standing, urinary pH becomes alkaline because
¾ Alkaline urine specimens tend to cause hemolysis of
red cells and disappearance of casts
¾ High protein diets will cause excessively acidic urine
¾ Ammonium chloride and mandelic acid may produce
¾ Alkaline urine after meals is a normal response to the
secretions of HCl in gastric juices
¾ Sodium bicarbonate, potassium citrate, and
acetazolamide may produce alkaline urine.
¾ Only a freshly voided sample is suitable for measuring
pH. Refrigerate the sample if any delay is expected
¾ Alkaline urine occurs from vegetarian diets, citrus
fruits, milk and other dairy products (Table 5.2)
¾ Highly concentrated urine such as that formed in
hot, dry environments is strongly acidic and may be
¾ While sleeping, decreased pulmonary ventilation
causes respiratory acidosis and urine becomes highly
¾ Chlorothiazide diuretic will cause acidic urine to be
¾ Bacterial contamination and overgrowth will result
in alkaline urine. Bacteria in urine will convert to
Important in fresh specimens only and is aromatic because
of volatile fatty acids. Bacterial action causes ammoniacal
odor, while ketosis leads to a fruity odor in urine.
It depends upon the concentration of various solutes in
1. Urinometer: Urine should be foamless. Transfer urine
(about 70 to 80 mL) into the urinometer container and
let the urinometer float freely without touching the
sides or the bottom of the container (Fig. 5.1). Read
graduations at the lowest level of urinary meniscus. If
the urine amount is less, dilute the urine to raise the
volume till 70 to 80 mL, take the reading and multiply
the last two digits by the dilution factor.
2. Refractometer: Only small amount of urine is needed.
It measures the concentration of solutes (related
to refractive index). In Goldberg refractometer, the
specific gravity of urine can be read directly from the
3. Can be tested with Dipsticks also.
4. Osmometry: Gives the most accurate assessment.
Correction factor for temperature: While using urinometer,
add or subtract 0.001 for each 3° C above or below the
standardization temperature of the instrument.
Urines of low specific gravity are called hyposthenuric
(< 1.007) while urines of fixed specific gravity of about
1.010 are known as isosthenuric.
Low specific gravity: (less than 1.010)
¾ All causes of polyuria except diabetes mellitus.
Low and fixed specific gravity: (1.010 to 1.012)
¾ Chronic nephritis (end-stage kidney) when concen -
tration power of renal tubules is low
¾ Specific gravity is maximum in the first morning sample
¾ Specific gravity is increased whenever there is an
excessive loss of water. It occurs in:
¾ Drugs leading to false positive:
• Radiopaque contrast media used in X-rays of the
¾ Temperature of urine specimens affects specific gravity
when specific gravity is measured in urine removed
from the refrigerator. Specific gravity will be falsely
¾ Reagent strip testing of urine containing glucosed urea
greater than 1% may cause a low specific gravity. Highly
buffered alkaline urine may also cause a low reading
¾ Elevated reading may occur in presence of moderate
(100 to 750 mg/dL) amounts of proteinuria.
The average 24 hours urinary output in an adult is around
1200 to 1500 mL and the night urine should not be more
A volume more than 2000 mL is termed polyuria.
Oliguria implies excretion of urine less than 500 mL and
anuria is complete cessation. Nocturia is excretion by an
adult of urine more than 500 mL with a specific gravity of
less than 1.018 at night (characteristic of chronic glomerulonephritis).
¾ Addison’s disease, decrease of adrenocortical
¾ Acute renal tubular necrosis
¾ Obstruction to urinary outflow.
possible abnormality such as the presence of pus, RBCs or
bacteria. Sometimes, however, excretion of cloudy urine
may not be abnormal since the change in urine pH may
cause precipitation within the bladder of normal urinary
constituents. Alkaline urine may appear cloudy because
of presence of phosphates, and urine may appear cloudy
¾ Pathologic urines are often turbid or cloudy, but so are
many normal urines. Cloudy urine may appear from
precipitation of crystals due to rapid cooling of the
¾ Occasionally, urine turbidity may result from urinary
¾ Abnormal urines may be cloudy on account of presence
of RBCs, pus cells or bacteria.
¾ After ingestion of food, urates or phosphates may
produce cloudiness in normal urine
¾ Vaginal contamination in female patients is often a
¾ Greasy cloudiness may be caused by lipiduria
¾ Many normal urines will develop haziness or turbidity
after being refrigerated or on standing at room
Normal values—negative (2 to 8 mg/dL)
If urine is not clear—filter or centrifuge the specimen. Both
bile and protein cause urine to froth.
Take a test tube 2/3rd full with urine, boil upper portion of
urine for 2 minutes (lower portion is not heated so that it
can be used as a control for comparing). Now turbidity can
arise because of phosphates, carbonates or protein. Add a
few drops of 10% acetic acid, persistence or development
of turbidity implies proteinuria.
False-positive tests may occur with X-ray contrast media
+ Definite cloudiness, but no granularity and no
++ Granular cloudiness, but no flocculation. Seen from
above, the cloud is dense but not opaque. Protein
+++ Dense opaque cloud, clearly flocculated. About 0.2
++++ Very thick precipitation, almost a solid. Protein
Urine should be clear and acid.
To 1 mL of urine, add 3 drops of 20% sulfosalicylic acid.
Absence of cloudiness means absence of protein. If the
turbidity persists after boiling, it is due to protein. If the
cloudiness vanishes on heating and reappears on cooling,
it is due to Bence-Jones (BJ) protein.
False positive test may appear if the urine contains
tolbutamide derivatives, high concentration of penicillin
Paper strips impregnated with Bromophenol blue and
salicylate buffer are dipped in urine. Presence of protein
is indicated by change of color from light yellow to blue.
Tolbutamide, X-ray contrast media and preservatives
do not react, hence no false positive tests. However,
highly alkaline urine may cause a false positive test;
(sensitivity—30 mg% or more). Tablets of similar reagents
producing the same color are also available.
Quantitative Estimation of Protein in Urine
1. Turbidimetric and chemical procedures: Provide an
accurate estimation. Colorimetric readings taken
against blanks and calculations done accordingly
give the result (example; sulfosalicylic acid turbidity
2. Esbach’s quantitative method: Acidify the urine if
necessary. Cover the bottom of the Esbach tube with
pumice, fill urine till the ‘U’ mark and add Esbach’s
or Tsuchiya’s regent till the ‘R’ mark. Stopper the tube
and invert it about a dozen times slowly.
Set the tube vertically and read after 30 minutes (if
pumice has not been used, read after 24 hours). The tube
is graduated to read in percent or in grams of protein per
liter at the top of the sediment. Urine may be diluted for
obtaining greater accuracy. After diluting, the Esbach tube
reading may be multiplied by the dilution factor (Fig. 5.2).
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