Dipstick Assay for Urinalysis
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Transcript of Dipstick Assay for Urinalysis
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7/27/2019 Dipstick Assay for Urinalysis
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Chemical Test Principles
Dipstick Assay for Urinalysis
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Bayer Multistix Product Insert
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7/27/2019 Dipstick Assay for Urinalysis
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Dipstick
Dipstick or reagent strips
Strip of plastic containing small pads of reagents
Each pad contains a colorimetric reagent to
detect a different analyte Color generated is proportional to concentration
of the analyte present in the sample.
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Dipstick Assay Analytes
1. Glucose
2. Bilirubin
3. Ketones4. Specific Gravity
5. Blood
6. pH
7. Protein
8. Urobilinogen9. Nitrite
10. Leukocytes
Available in commercial urine
dipsticks
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Test Principle - Glucose
Reagents on the dipstick:
EnzymesGlucose Oxidase, Peroxidase
ChromogensPotassium Iodide,
Tetramethylbenzene, o-tolidene, 4-
Aminoantipyrene
Note:
1) This test will work only for glucose. Other sugars such assucrose, lactose, galactose and fructose cannot be detected.
2) Other reducing sugars can be detected using the Benedicts test.
However, this involves a heating step. The sensitivity of the
Glucose Oxidase method is more than that of a Copper reduction
test such as Benedicts test.
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Test Principle - Bilirubin
Reagents on strip:
2,4-dichloroanilene diazonium salt,
2,4-dichlorobenzene diazonium salt
Note:
1) This test may give false negatives upon
prolonged exposure of the urine sample to light.
Bilirubin is photosensitive, and gets converted
into Biliverdin upon light exposure.
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Test Principle - Ketones
Reagents on strip: Sodium Nitroprusside
Note:1) This test will not detect Acetone or
hydroxybutyric acid.
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Test Principle - Blood
Reagents on the strip:
Diisopropylbenze dihydroperoxide,
3,3,5,5-tetramethylbenzidine
Note:
1) This test can usually show free Hb, myoglobin as well asRBCs. Upon testing, RBCs will lyse, and form a speckled
pattern on the pad.
2) False positives may arise from the presence of oxidizing
contaminants in the sample.
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Test Principle Specific Gravity
X+ + Polymethyl vinyl ether / maleic anhydride
---------------> X+-Polymethyl vinyl ether / maleic anhydride + H+
H+ interacts with a Bromothymol Blue indicator to
form a colored complex
Reagents on stripPoly(methyl vinyl ether/
maleic anhydride) , Sodium Hydroxide,
Bromothymol Blue
1.000
1.005
1.010
1.015
1.020
1.025
1.030Note:
1) These readings will not be accurate in case
the urine is alkaline.
2) Test does not measure non-ionized solutes
such as glucose.
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Test Principle - pH
H+ ions react with Methyl Red and
Bromomethyl Blue indicators to form
coloured complexes.
Methyl Redhigh conc. of H+ , low pH
Bromothymol Bluelow conc. of H+ ,
high pH
Reagents on strip : Bromothymol Blue,
Methyl Red
Note:1) These reagents can indicate pHs between 5.0 and 8.5.
2) Values of pH may be affected by certain medications, or
bacterial growth in the sample.
3) In a commerical dipstick, buffers from the next reagent
zone for protein may also run-over into the pH zone andprovide an incorrect value.
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Test Principle - Protein
Based on the Protein Errors of Indicators
method. The point of colour change of some
indicators is different in the presence of a protein
than in the absence of the protein. This is due to
proton accepting behavior of proteins at a
constant pH
Reagents on strip:
Tetrabromphenol, acidic buffer.
Note:
1) Test is sensitive to albumin, but not to globulins,
Bence-Jones proteins, and muco-proteins.
2) Highly alkaline urine will lead to false positives.
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Test Principle - Urobilinogen
Ehrlich Aldehyde Reaction
Reagents on strip:
Paradiethylaminobenzaldehyde
Note:
1) Several interfering substances such as p-
aminosalicylic acid, sulfonamides, p-aminobenzoic
acid may react with the reagent.
2) Test cannot indicate the absence of Urobilinogen.
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Test Principle - Nitrite
Reagents on strip : Para-arsanilic acid,
1,2,3,4-tetrahydrobenzo (h)-quinolin-3-ol
Note:1) Bacterial overgrowth in sample with
interfere with the test.
2) Can only detect bacteria than reduce nitrate
to nitrite.
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Test Principle Leukocytes
Reagents on strip: Derivatised
pyrrole amino acid ester/ indoxyl
ester derivative, diazonium salt
Note:
1) False positives may occur in case strong oxidizing
contaminants are present
2) False negative may occur if the specific gravity is
high due to glucose or protein.
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List of Reagents from a Product
Insert
UrinCheck Healthscreen 10, Express Diagnostics, USA
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References
Graffs Textbook of Routine Urinalysis & BodyFluid, Chapter 4
Urinalysis - Francisco G. La Rosa, University of
Colorado
UrinCheck HealthScreen 10 product insert.
Practical Guide to Urine Analysis, Clinitek ProductInsert