M3U3: BLOOD, PORPHOBILINOGEN, BILIRUBIN, AND UROBILINOGEN Flashcards
What is the usual urine colour for specimens of hematuria and hemoglobinuria ?
range from normal, pink, red and brown
How does hematuria and hemoglobinuria differentiate in clarity ?
hematuria = cloudy/smoky appearance hemoglobinuria = clear
what would alkaline pH urine promote in specimens showing hematuria and hemoglobinuria ?
hematuria = lysis of intact cells hemoglobinuria = hemoglobin oxidation
for specimens of hematuria and hemoglobinuria, what is shown after centrifugation ?
hematuria = cell button hemoglobinuria = uniform clear red urine
what is detected in the chemical methods used in the detection of blood and hemoglobin ?
heme, and other compounds containing it such as myoglobin and cytochrome
what is the colour range observed in the reagent strip method for blood ?
yellow (negative) to green (positive)
What is impregnated in the reagent pad for blood ?
tetramethylbenzidine (chromogen) and peroxide
The ___ causes the reduction of peroxide and oxidation of the chromogen, producing a colour change on the reaction pad.
pseudoperoxidase activity of the heme moiety
What is the chemical equation for the chemical reaction taking place in the reagent strip method for blood ?
H2O2 + Chromogen -> Oxidized chromogen + H2O
In the reagent strip method for blood ___ is observed when intact red cells are present and lysed on the reaction pad
mottled/speckled pattern
which brand of reagent strip in the method for blood uses dimethyldihydroperoxyhexane ?
chemstrip
Which brand of reagent strip detects 6-20 RBC/uL and 0.02-0.06 mg/dL ?
multistix
Which brand of reagent strip detects 5-10 RBC/uL and 0.02-0.03 mg/dL ?
chemstrip
What may be the cause for a false-positive result in the reagent strip method for blood ?
strong oxidizing agents (sodium hypochlorite) - oxidizes the chromogen instead of the heme moiety
bacterial peroxidases (from E. coli) - catalyzes the reaction of the reagent and chromogen despite the absence of the pseudoperoxidase activity of heme
blood contamination
What may be the cause for false-negative result in the reagent strip method for blood ?
ascorbic acid, reducing substances - tend to react directly with peroxide impregnated on blood reagent pad and removes it from the intended reaction, thereby preventing oxidation of the chromogen
procedural errors (e.g. failing to mix the sample prior to dipping the reagent strip)
high urine specific gravity - causes intact red cells in urine to become crenated and resist lysis which is necessary to detect heme
increased urine nitrite (>10 mg/dL)
presence of formalin
Originally, at what concentration is multistix and vchem brand of reagent strips affected by ascorbic acid on the blood test ? and after the modification ?
multistix = ≥9 mg/dL vchem = ≥5 mg/dL
25 mg/dL
What modifications where done on the multistix and chemstrip reagent strip to reduce interference with ascorbic acid ?
multistix = uses a peroxide that is less subject to reduction by ascorbic acid
chemstrip = overlays the reagent pad with an iodate-impregnated mesh that oxidizes ascorbic acid prior to reaching the reaction pad
what is the principle of the salt precipitation method (blondheim test) qualitative test for blood ?
larger hemoglobin molecules are precipitated by ammonium sulfate and myoglobin remains in the supernatant
what is the possible results for the blondheim test ?
myoglobin present = supernatant (red), blood reagent strip (positive)
hemoglobin present = red precipitate, blood reagent strip of supernatant (negative)
what is the principle of the benzidine test in other qualitative tests for blood ?
In the presence of the pseudoperoxidase activity of hemoglobin or myoglobin, hydrogen peroxide is decomposed to water and oxygen.
The liberated oxygen oxidizes benzidine to a green or blue colour
what is the principle of the occult tablet test in other qualitative tests for blood ?
sodium carbonate + tartaric acid = CO2
- effervescence to facilitate the reaction
Tartaric acid and calcium acetate + strontium peroxide = hydrogen peroxide
- in the presence of pseudoperoxidase activity of hemoglobin or myoglobin, hydrogen peroxide is decompose to water and oxygen
Liberated oxygen oxidizes o-toluidine to a blue colour
red dye is added to mask discolouration of the tablet by blood
What is the result for Guaiac test in other qualitative tests for blood ?
green to blue colour at the zone of contact
What is the principle of Guaiac test in other qualitative tests for blood ?
liberated oxygen from pseudoperoxidase activity of hemoglobin or myoglobin oxidizes the phenols present in guaiac to quinones
what is the result for occult tablet test in other qualitative tests for blood ?
blue colour within 2 minutes
