Test 3: Review Flashcards
What are the handling requirement’s for reagent strips?
-Store with desiccant in an opaque, tightly sealed container
-Remove strips immediately –prior to use
-Store below 30C
-Do not use past the expiration date
-Visually inspect for discoloration/deterioration
Why is it important to mix specimens before testing?
Formed elements such as red and white blood cells sink to the bottom of the specimen and will be undetected in an unmixed specimen
What happens when a urine specimen remains at room temp for an extended period of time?
Bacteria can begin to grow rapidly causing a falsely alkaline urine and give the urine a cloudy-hazy appearance.
How do reagent test strips work for testing blood?
The pseudoperoxidase action of erythrocytes and hemoglobin catalyzes the oxidation of various chromogens to produce the color change.
What can cause false positives on the blood reagent test strip?
oxidizing contaminants (bleach), microbial peroxidase. Very sensitive.
What can cause false negatives on the blood reagent test strip?
formalin, excess nitrites, elevated specific gravity and Captopril may reduce reactivity.
How do reagent test strips work for testing bilirubin?
Bilirubin in the urine couples with a diazonium salt in an acid medium.
What can cause false negatives on bilirubin test strips?
samples exposed to light will show decreased amounts of bilirubin; excess levels of ascorbic acid.
What can cause false positives on bilirubin test strips?
highly colored metabolites of drugs may interfere with reading the reaction and appear as false positives.
How do the reagent test strips work for testing glucose?
The color is produced through a double enzymatic reaction of glucose oxidase and peroxidase. The latter enzyme reacts with a chromogen to produce the final color.
What can cause false negatives on glucose reagent test strips?
elevations of ketones; very elevated specific gravities; excess levels of ascorbic acid.
What can cause false positives on glucose reagent test strips?
presence of oxidizing agents (bleach).
How do the reagent test strips work for testing ketones?
Ketones react with nitroprusside or sodium nitroferricyanide and glycine to produce a color change.
What can cause false positives on ketone reagents strip testing?
presence of phenylketone or phthalein compounds; highly pigmented urines; some drug metabolites.
What are the limitations with ketone reagent strip testing?
Only detects acetoacetate and acetone, not Beta hydroxybutyrate that is common in diabetes and nutritional disorders.
How do reagent test strips work for testing nitrites?
Nitrates in the urine are converted to nitrites by the action of gram negative bacteria. These nitrites then react to form a diazonium salt which in turn reacts with a chromogen to produce the final color.
What can cause false negatives with nitrite reagent test strips?
excess ascorbic acid. Animals false negatives; not reliable.
What can cause false positives with nitrite reagent test strips?
presence of red dyes or other chromogens.
How do reagent test strips work for testing pH?
A double indicator system detects the amount of hydrogen ions in the urine to produce a color change.
What animals usually have more acidic pH?
What animals usually have a more alkaline pH?
carnivores
herbivores
What testing error can cause issues with pH reagent test strips?
If excess urine is left on the reagent strip, a phenomenon known as runover may occur. The urine from one reagent area carries reagent onto the pH test area and changes the result erroneously.
How do reagent test strips work for protein?
: This reaction is based on the phenomenon known as the “protein error of indicators” where an indicator that is highly buffered at a pH of 2 will change color in the presence of proteins (anions) as the indicator releases hydrogen ions to the protein.
What can cause false positives on protein reagent test strips?
Strongly basic urine; presence of phenazopyridine, polyvinylpyrrolidone, chlorhexidine, and bleach.
What will give the best sample for urobilinogen testing?
Excretion of urobilinogen is enhanced in alkaline urine, a sample that is voided two hours after a meal is best.
How do reagent test strips work for urobilinogen?
Urobilinogen reacts with a chromogen to form an azo dye which appears as various shades of pink or purple. This reaction occurs best at room temperature.
What can cause false negatives with urobilinogen reagent test strips?
Excess nitrites; presence of formalin.
What can cause false positives with urobilinogen reagent test strips?
Presence of phenazopyridine; very warm urine.
How do reagent test strips work for leukocytes?
Leukocyte esterase, present in granulocytes, catalyzes the reaction of the chromogens to produce a color change.
What can cause false negatives with leukocyte reagent test strips?
Gentamicin, elevated glucose and protein concentrations, tetracycline.
What can cause false positives with leukocyte reagent test strips?
Drugs producing red urine, vaginal contamination. Notes: Generally not reliable in animals.
How do reagent test strips work for specific gravity?
This reaction is based on change of an indicator color in the presence of high concentrations of various ions.
Test strips for specific gravity are not reliable in animals. Scale is not high enough for many species.
What should be used to get a reliable reading?
refractometer
Confirmatory test that will detect other sugars such as lactose, fructose, galactose, and pentoses. These other sugars may signify metabolic disorders when found in the urine of small children
Clinitest - Copper reduction test
Ketone test that can be used as a backup or to evaluate questionable results, but affected by same interferences seen on dipstick
ACEtest for Ketones
True or false:
The ACEtest is a ketone confirmatory test?
False
What does a positive result look like for the ACEtest?
varying levels of purple = positive
no color change = neg.
What does the ACEtest for ketones tablet contain?
sodium nitroprusside, glycine, disodium phosphate, lactose (gives better color)
What is the confirmatory test for bilirubin?
ICTOtest – Diazo Tablets
What is the difference between bilirubin strip tests and the ICTO test?
Same principle as strip but picks up LOWER levels
What does a positive ICTO test look like?
Positive = blue-to-purple color
For example, what does it mean if ketones or blood reactions are positive?
?
Ketones are formed during the catabolism of _________.
fatty acids
A positive ketone test may signify diabetic ___________.
ketoacidosis
Any amount of BLOOD greater than ____ cells per microliter of urine is considered clinically significant.
5
What is it called when there are intact RBCs in the urine?
Can make a cloudy red appearance.
Hematuria
What are possible causes of hematuria?
-Glomerular disease
-Pyelonephritis or cystitis
-Renal calculi
-Tumor
-Trauma, hypertension, exercise, smoking, meds and other toxins
product of RBC destructions – clear red urine
Hemoglobinuria
What are possible causes of hemoglobinuria?
-Intravascular hemolysis from transfusion reactions, hemolytic anemia, paroxysmal nocturnal hemoglobinuria
-Infections – malaria
-Chemical toxicity – copper, nitrates, nitrites
-Exertional hemolysis