Urine is produced by the kidney to maintain constant plasma osmotic
concentration; to regulate pH, electrolyte and fluid balances and to excrete some
50 grams of waste solids (mostly urea and sodium chloride). Texts on human
anatomy and physiology describe in detail the function and mechanism by which
the kidney's nephrons accomplish this.

Some normal urine constituents excreted (in g/24 hours):


                Urea            25-30
                Uric acid       0.6-0.7
                Creatinine      1.0-1.2
                Hippuric acid   0.7
                Ammonia         0.7
                Amino acids     3
                Sodium          1-5 (NaCl 15.0)
                Potassium       2-4
                Calcium         0.2-0.3
                Magnesium       0.1
                Chloride        7
                Phosphate       1.7-2.5
                Sulfate         1.8-2.5

Routine urinalysis is composed of Chemical tests for abnormal chemical
constituents
               

PROCEDURES

The color and appearance of the urine specimen is recorded. Usual colors are colorless,
straw, yellow, amber; less commonly pink, red, brown. Usual appearances (opacity)
are clear or hazy; less commonly turbid, cloudy and opaque, unless the specimen has
remained at room or refrigerated temperatures.

METHODOLOGIES AND INTERPRETATIONS

Glucose:
This test is based on a double sequential enzyme reaction. One enzyme, glucose
oxidase, catalyzes the formation of gluconic acid and hydrogen peroxide from the
oxidation of glucose. A second enzyme, peroxidase, catalyzes the reaction of
hydrogen peroxide with a potassium iodide chromogen to oxidize the chromogen to
colors ranging from green to brown.

In general the presence of glucose indicates that the filtered load of glucose exceeds
the maximal tubular reabsorptive capacity for glucose. In diabetes mellitus, urine
testing for glucose is often substituted for blood glucose monitoring.


Bilirubin:
This test is based on the coupling of bilirubin with diazotized dichloroanaline in a
strongly acid medium. The color ranges through various shades of tan.

Bilirubin in the urine indicates the presence of liver disease or biliary obstruction.
Very low amounts of bilirubin can be detected in the urine, even when serum levels
are below the clinical detection of jaundice.


Ketone:
This test is based on the development of colors ranging from buff-pink, for a
negative reading, to purple when acetoacetic acid reacts with nitroprusside.

Urine testing only detects acetoacetic acid, not the other ketones, acetone or
beta-hydroxybuteric acid. In ketoacidosis (insulin deficiency or starvation), it can
be present in large amounts in the urine before any elevation in plasma levels.


Specific Gravity: 

This test is based on the apparent pKa change of certain pretreated polyelectrolytes,
poly(methyl-vinyl-ether/maleic anhydride), in relation to ionic concentration. In
the presence of bromthymol blue, colors range deep blue-green in urine of low ionic
concentration through green and yellow-green in urines of increasing ionic
concentration.

The specific gravity is a convenient index of urine concentration. It measures
density and is only an approximate guide to true concentration. A specific gravity
of <1.010 is consistent with a concentrating defect. A specific gravity of >1.025, in
the absence of protein, glucose and other large molecular weight substances such
as contrast media, usually indicates normal renal concentration and makes chronic
renal insufficiency unlikely.


Blood:
This test is based on the peroxidase-like activity of hemoglobin, which catalyzes the
reaction of diisopropylbenzene dihydroperoxide and 3,3',5,5'-tetramethylbenzidine.
The resulting color ranges from orange through green; very high levels of blood
may cause the color development to continue to blue.

The presence of large numbers of RBCs in the urine sediment establishes the 
presence of hematuria. If the dipstick is more strongly positive than would be
expected from the number of RBCs, then the possibility of hemoglobinuria or
myoglobinuria should be considered.


pH:
The test is based on the double indicator (methyl red/bromthymol blue) principle
that gives a broad range of colors covering the entire urinary pH range. Colors
range from orange through yellow and green to blue.

The urine pH should be recorded, although it is seldom of diagnostic value.
Phosphates will precipitate in an alkaline urine, and uric acid will precipitate in
an acidic urine.


Protein:
This test is based on the protein-error-of-indicators (tetrabromphenol blue)
principle. At a constant pH, the development of any green color is due to the
presence of protein. Colors range from yellow for negative through yellow-green
and green to green-blue for positive reactions.

Heavy proteinuria usually represents an abnormality in the glomerular filtration
barrier. The test is more sensitive for albumin than for globulins or hemoglobin.


Urobilinogen:
This test is based on the modified Ehrlich reaction, in which
para-diethylaminobenzaldehyde in conjunction with a color enhancer reacts with
urobilinogen in a strongly acid medium to produce a pink-red color.

Urine urobilinogen is increased in any condition that causes an increase in
production or retention of bilirubin.


Nitrite:
This test depends upon the conversion of nitrate (derived from the diet) to nitrite by
the action of Gram negative bacteria in the urine. At the acid pH of the reagent
area, nitrite in the urine reacts with para-arsanilic acid to form a diazonium
compound. This diazonium compound in turn couples with
1,2,3,4-tetrahydrobenzo(h)quinoline-3-ol to produce a pink color.

Bacteriuria caused by some Gram negative bacteria which produce the nitrate
reductase enzyme give a positive test.


Leukocytes:
Granulocytic leukocytes contain esterases that catalize the hydrolysis of the
derivatized pyrrole amino acid ester to liberate 3-hydroxy-5-phenyl pyrrole. This
pyrrole then reacts with a diazonium salt to produce a purple product.

A positive leukocyte esterase test provides indirect evidence for the presence of
bacteriuria.

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