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Urinalysis Reagent Strips
Expected Results and Technical Discussion
All Ten (10) Parameters
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Urine diagnostic* reagent strips
are available to initially screen for up to ten (10) specific chemical
components, or potential components, in urine.
*Any diagnosis from the results obtained
using urinalysis reagent strips should be preliminary only and presumed suspect
with further quantitative and symptomatic analysis required for confirmation of
any specific medical condition.
• Glucose: The glucose reagent panel is specific
for glucose; no substance other than glucose is known to give a positive result.
The reactivity of the glucose test decreases as the Specific Gravity of the
urine increases. Reactivity may also vary with temperature. Small amounts of
glucose may normally be excreted by the kidneys, these amounts are usually below
the sensitivity range of this test but on occasion may produce a color between
the 'Negative' and the 100/5 color block and may be interpreted by the observer
as positive. Glycosuria is the condition of glucose in urine. Normally the
filtered glucose is reabsorbed by the renal tubules and returned to the blood by
carrier molecules. If blood glucose levels exceed renal threshold levels, the un-transported
glucose will spill over into the urine. Main cause: diabetes mellitus
•
Ketones: This test reacts with
acetoacetic acid in urine. It does not react with acetone or b‑hydroxybutyric
acid. Some high specific gravity/low pH urines may give reactions up to and
including 'Trace'. Normal urine specimens usually yield negative results with
this reagent. False positive results (trace or less) may occur with high
pigmented urine specimens or those containing large amounts of levodopa
metabolites. Ketone bodies such as acetoacetic acid, beta-hydroxybutyric acid,
and acetone can appear in urine in small amounts. These intermediate by-products
are associated with the breakdown of fat. Causes: diabetes mellitus, starvation,
diarrhea.
•
Blood: The significance of the 'Trace'
reaction may vary among patients, and clinical judgment is required for
assessment in an individual case. Development of green spots (intact
erythrocytes) or a green color (free hemoglobin / myoglobin) on the reagent area
within 60 seconds indicates the need for further investigation. Blood is often
found in the urine of menstruating females. This test is highly sensitive to
hemoglobin and thus compliments the microscopic examination. This test is
equally sensitive to myoglobin as to hemoglobin. The sensitivity of this test
may be reduced in urines with high specific gravity. Captopril may cause
decreased reactivity. False positives reactions can be caused by certain
oxidizing contaminants such as hypochlorite ‑ microbial peroxiclase associated
with urinary 'tract infection may also give a false positive reaction. Levels of
ascorbic acid normally found in urine do not interfere with this test.
Hemoglobinuria is the presence of hemoglobin in the urine. Causes: hemolytic
anemia, blood transfusion reactions, massive bums, renal disease Hematuria is
the presence of intact erythrocytes. Almost always pathological. Causes: kidney
stones, tumors, glomerulonephritis, physical trauma,
urinary tract infection, Prostatitis.
• pH: The pH
test area measures pH values generally within 1 unit in the range of 5 ‑ 8.5
visually and 5 ‑ 9 instrumentally with 5 being very acidic
and 8.5 being highly alkaline. Generally, urine
pH results range from 5.5 -
7.5 in a bell curve type statistical distribution. Average
for normal human urine is slightly acidic 6.0,
however deviations from normal in any given sample are
unremarkable and consistent, repeated readings are required in the top or bottom
range to suggest an abnormality. High
protein diets increase acidity. Vegetarian diets increase alkalinity. Bacterial
infections also increase alkalinity producing a urine pH in
the higher 7-8 range.
• Protein: The reagent area is more sensitive to
albumin than to globulins, hemoglobin, and mucoprotein. a 'Negative' result
does not rule out the presence of other proteins. Normally no protein is
detectable in urine by conventional methods, although a minute amount is
excreted by the normal kidney. A color matching any block greater than 'Trace'
indicates significant proteinuria. For urine of high specific gravity, the test
area may most closely match the 'Trace' color block even though only normal
concentrations of protein are present. Clinical judgment is needed to evaluate
the significance of 'Trace' results. False positive results may be obtained with
highly alkaline urines. Albumin is normally too large to pass through glomerulus
tissue. Therefore elevated results Indicate abnormal increased permeability of
the glomerulus membrane. Non-pathological causes are: pregnancy, physical
exertion, increased protein consumption. Pathological causes are:
glomerulonephritis bacterial toxins, chemical poisons.
•
Nitrite: This test depends upon the
conversion of nitrate (derived from the diet) to nitrite by the action of
principally gram negative bacteria in the urine. The test is specific for
nitrite and will not react with any other substance normally excreted in urine.
Pink spots or pink edges should not be interpreted as a positive result. Any
degree of uniform pink color development should be interpreted as a positive
nitrite test suggesting the presence of 100000 or more organisms per ml, but
color development is not proportional to the number of bacteria present. A
negative result does not in itself prove that there is no significant
bacteriuria. Negatives may occur when urinary tract infections are caused by
organism which do not contain reductase to convert nitrate to nitrite; when
urine has not been retained in the bladder long enough (4 hours or more) for
reduction of nitrate to occur; or when dietary nitrate is absent, even if
organisms containing reductase are present and the bladder incubation is ample.
Sensitivity of the nitrite test is reduced for urines with a high specific
gravity. High abnormal readings indicate the presence of bacteria. Causes:
urinary tract infection.
• Leucocytes: Normal
urine specimens generally yield negative results; positive results of small (+)
or greater are clinically significant. Individually observed 'Trace' results may
be of questionable clinical significance; however, 'Trace' results observed
repeatedly may be clinically significant. 'Positive' results may occasionally be
found with random specimens from females due to contamination of the specimen by
vaginal discharge. Elevated glucose concentrations or high specific gravity may
cause decreased test results. The presence of leukocytes in urine is referred to
as pyuria (pus in the urine). Primary cause: urinary tract infection,
Prostatitis.
•
Urobilinogen: This test area will detect
urobilinogen in concentrations as low as 3 mIU/L in urine. The reagent area may
react with substances known to interfere with Ehrlich's reagent, such as
p‑aminosalicylic acid and sulphonamides. Atypical color reactions may be
obtained in the presence of high concentrations of p‑aminobenzoic. False
negative results may be obtained if formalin is present. Highly colored
substances, such as azo dyes and riboflavin may mask color development on the
reagent area. Strip reactivity increases with temperature; the optimum
temperature is 22‑26 degrees centigrade. The absence of urobilinogen cannot be
determined with this test. Bile pigment derived from breakdown of hemoglobin.
The majority of this substance is excreted in the stool, but small amounts are
reabsorbed into the blood from the intestines and then excreted into the urine.
Causes: hemolytic anemia, liver diseases.
• Specific Gravity: The specific gravity test
permits the determination of urine specific gravity between 1.000 and 1.030. In
general, it correlates within 0.005 with values obtained with the refractive
index method. For increased accuracy, 0.005 maybe added to readings from urine
with pH equal to or greater than 6.5. Elevated specific gravity readings may be
obtained in the presence of moderate quantities (1‑7.5 g/L) of protein. The
specific gravity of urine is a measurement of the density of urine; the relative
proportions of dissolved solids in relationship to the total volume of the
specimen. It reflects how concentrated or diluted a sample may be. Water has a
specific gravity of 1.000. Urine will always have a value greater than 1.000
depending upon the amount of dissolved substances (salts, minerals, etc.) that
may be present. Very dilute urine has a low specific gravity value and very
concentrated urine has a high value. Specific gravity measures the ability of
the kidneys to concentrate or dilute urine depending on fluctuating conditions.
Normal range 1.005 - 1.030, average range 1.010 - 1.025. Low specific gravity is
associated with conditions like diabetes insipidus, excessive water intake,
diuretic use or chronic renal failure.
•
Bilirubin: Normally no bilirubin is
detected in urine by even the most sensitive methods. Even trace amounts of
bilirubin are sufficiently abnormal to require further investigation. Atypical
result colors may indicate bile pigment abnormalities and the urine specimen
should be tested further by more quantitative laboratory means. Metabolites of
drugs which give a color at low pH, such as Pyridium and Serenium may cause
false positives. Ascorbic acid concentrations of 1.42 mIU/L or greater may cause
false positives. Bilirubin comes from the breakdown of hemoglobin in red blood
cells. The globin portion of hemoglobin is split off and the heme groups of
hemoglobin are converted into the pigment bilirubin. Bilirubin is secreted in
blood and carried to the liver where it is conjugated with glucuronic acid. Some
is secreted in blood and some is excreted in the bile as bile pigments into the
small intestines. Causes: liver disorders, cirrhosis, hepatitis, obstruction of
bile duct.

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