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53 Cards in this Set
- Front
- Back
What's the other name for Group strep A?
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Strep pyogenes
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What are the cellular antgens on Strep A?
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-M protein
-Group-specific polysaccharide |
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What extracellular products does Strep A produce?
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-Streptolysin O
-Streptokinase -Hyaluronidase -DNAse A/B/C/D -Proteinase/Esterase/Amylase -Erythrogenic toxin |
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What are suppurative strep infections?
Nonsuppurative? |
ones producing pus;
ones not producing pus |
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What are the suppurative strep infections?
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-pharyngitis/tonsilitis/strep throat
-scarlet fever -impetigo/pyoderma -cellulitis -sinusitis/otitis media -pneumonia -stss -necrotizing fasciitis |
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what are the nonsuppurative strep infections?
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-Rheumatic fever
-Acute glomerulonephritis |
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why are some infections better tested serologically?
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if the infectious organism is not obtainable on a specimen.
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which infections may be better tested with serologic methods?
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cellulitis/skin infections
sinusitis/otitis media finish this one |
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what are 4 serological tests for strep A?
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1. Antistreptolysin O (ASO)
2. ASO Latex agglutntion-rapid 3. Anti-DNAse B (ADN-B) 4. Anti-Hyaluronidase (AHT) |
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What type of specimen is best for any of them?
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Paired sera, 3 weeks apart
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what if no paired sera is available?
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Compare the convalescent specimen to a reference range.
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How does the ASO classic test work?
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1. Serum + Streptolysin O added, incubate 15 min at 37'C.
2. Add 5% RBC suspension, incubate 30 min at 37'C. 3. Centrifuge, look for hemolysis |
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In the classic ASO, what is:
-Positive -Negative |
Pos = no hemolysis
Neg = hemolysis; no ASO was present to neutralize the antigen added, so it bound to RBCs and caused lysis. |
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What type of RBCs are used in the ASO test?
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-Human group Oneg
-Rabbit RBCs |
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How is the titer reported in the ASO test?
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The reciprocal of the highest dilution showing NO HEMOLYSIS.
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What is the ref range for ASO?
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<166 Todd units
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What controls are run with the ASO?
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1. RBC control - only cells, to make sure not auto-hemolysis.
2. ASO control - Buffer, reagent, and RBCs to make sure hemolysis CAN occur. 3. Standard - to see what 166 Todd units looks like. |
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What are 3 sources of error in the classic ASO test?
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1. Oxidation of reagent from shaking/aerating vial
2. Reconstituted reagent older than 10 minutes. 3. Lipoprotein, cholesterol, bacterial contamination. |
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How does the rapid ASO test work?
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1. Latex beads coated with antigen (streptolysin O).
2. Add serum; look for agglutination. |
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What should occur if the rapid ASO is positive?
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The lab tech should do a quantitative test.
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What is the ref range for the rapid aso test?
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<200 U/ml
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What are 4 sources of error in the rapid ASO?
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1. Bacterial contamination
2. Reaction read beyond 3 min 3. Lipemic serum - nonspecific 4. Subjective readings |
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Along with the classic/rapid ASO tests, what is used for Strep A?
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ADN-B test
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What type of test is the ADN-B test?
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Neutralization test
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What is the ADN-B principle?
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-Serum and Strep DNAse B are incubated 20 min at body temp.
-Inc w/ DNA-methyl grn overnite Clear = neg; DNAse worked Green = pos; the strep's DNAse beat the added to substrate. |
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How do you report the titer of the ADN-B test?
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Reciprocal of highest dilution showing 3+ green.
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What is the ADN-B ref range for
-preschoolers -other |
Preschool: <120
Other: <1360 |
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What mainly causes error in the ADN-B test?
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dnase from organisms other than StrepA
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What is one other test that can be used but is uncommon?
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AHT - anti-hyaluronidase test
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What is the advantage of the ASO test?
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-ASO titer rises within 7 days of disease onset.
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What are disadvantages of the ASO test?
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-Many people have low titers already, b/c of freq. exposure.
-Strep skin infections may produce low titers, undetected -False + from rising titer in rheumatic fever. -Only half of glomeruloneph. patients show high titer. |
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What is the advantage of the ADN-B test?
What is its limitation? |
-Most reliable test for Strep A
but.... Titer rises later than ASO. |
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What disease is Mycoplasma pneumoniae responsible for?
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walking pneumonia
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How is M. pneumoniae tested for?
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-Culture but it takes up to a month to grow!
--Serology |
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What 3 serological methods are used for mycoplasma?
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1. Complement fixation
2. EIA 3. Cold agglutinins |
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What is the principle of the cold agglutinins test?
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M. pneumoniae agglutinates human group O RBCs in the cold.
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What are limitations of the cold agglutinins test?
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-The agglutinins are only in 50% of cases.
-Other viral resp diseases can also stimulate cold agglutinins. |
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what diseases are assoc. with Helicobacter pylori?
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-Gastritis
-Peptic ulcers |
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What 4 specimen types are tested for H. pylori? How?
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1. Mucosa - Endoscopic biopsy
2. Serum - Serology 3. Stool - EIA for Ag in 4. Breath - Urea tests |
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What is the CLO test?
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a urease test done on endoscopic biopsies for h. pylori.
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What do serological H. pylori tests look for?
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Antibody in serum to the bug.
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What are adantages and disadvntg of serological methods for h. pylori?
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Advntg: less invasive than endoscopic biopsy
Disadvntg: less specific and sensitive. |
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which test for h pylori is best? why?
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Urea breath tests - have the highest combined sens./specificty.
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What is febrile agglutinins testing used for?
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Identifying hard-to-grow microorganisms that often cause fever of unknown origin.
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What 4 bacterial diseases are included in a febrile agglutinin panel?
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1. Salmonella somatic/flagellar antigens (typhi/paratyphi)
2. Brucella abortus 3. Francisella tularensis 4. Rickettsia |
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What is the Weil-felix test?
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A presumptive test for Rickettsial antibodies
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What is the principle of the Weil-felix test?
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Rickettsia antibodies cause positive reaction
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what is the major limitation of the weil-felix test?
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-Antibody detected is heterophilic and nonspecific.
-If Proteus is causing the infection, will get a false pos. |
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what is the lab's role in diagnosing lymes disease?
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-Culture impractical - time
-Serology is most used method. |
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What are the problems with serological methods for lymes?
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-Tests/reagents not standardizd.
-Tests have low sensitivity |
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Which seroloical methods are used for screening lymes?
What specimens? |
IFA - lo volume
Elisa - hi volume -serum/csf |
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What confirms lymes diagnosis?
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-Four fold paired sera titer
-Western blot |
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what type of fluid can PCR be used on for lymes? What is the problem with this test type?
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-Synovial fluid
-Can detect both viable and nonviable lymes. |