ASCP M flashcards
ASCP M · Build recall with a focused review session.
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- Coagulase-positive gram-positive cocci
- Staphylococcus aureus forms gram-positive cocci in clusters, is catalase-positive, and is coagulase-positive; coagulase-negative staphylococci such as S. epidermidis are distinguished by a negative coagulase test.
- Optochin-sensitive gram-positive diplococci
- Streptococcus pneumoniae appears as gram-positive diplococci or short chains, is catalase-negative, alpha-hemolytic, optochin-sensitive, and bile-soluble; these features separate it from viridans streptococci.
- MacConkey lactose fermentation
- On MacConkey agar, lactose-fermenting gram-negative rods such as Escherichia coli produce pink colonies; non-lactose fermenters such as Salmonella and Shigella produce colorless colonies.
- Oxidase test
- The oxidase test detects cytochrome c oxidase activity; Pseudomonas aeruginosa is oxidase-positive, whereas Enterobacterales such as E. coli and Klebsiella are oxidase-negative.
- MRSA cefoxitin screen
- Cefoxitin disk diffusion or oxacillin MIC detects methicillin-resistant Staphylococcus aureus; resistance is mediated by mecA or mecC genes encoding an altered penicillin-binding protein.
- Bacteroides fragilis bile resistance
- Bacteroides fragilis is an anaerobic gram-negative rod that grows in 20% bile and is resistant to bile; it is the most common anaerobic pathogen in intra-abdominal infections.
- Fourth-generation HIV test
- Fourth-generation HIV screening detects HIV p24 antigen plus HIV-1/2 antibodies; a reactive result must be confirmed by HIV-1/2 antibody differentiation or nucleic acid testing.
- HBsAg
- Hepatitis B surface antigen indicates current hepatitis B virus infection, either acute or chronic; anti-HBs indicates immunity, and anti-HBc IgM indicates acute infection.
- Anti-HBc IgM
- IgM antibody to hepatitis B core antigen appears early in acute hepatitis B and is present during the window period when HBsAg has cleared but anti-HBs has not yet appeared.
- CMV owl's-eye inclusions
- Cytomegalovirus infection produces large intranuclear inclusions with a clear halo, described as owl's-eye inclusions; CMV DNA PCR and pp65 antigenemia are used for detection and monitoring.
- HCV RNA
- Hepatitis C virus RNA testing confirms active infection after a reactive anti-HCV screen and is used to monitor antiviral treatment response.
- Germ tube test
- Incubation of yeast in serum at 37°C for two to three hours produces germ tubes in Candida albicans and Candida dubliniensis, distinguishing them from germ tube-negative Candida species.
- India ink capsule
- India ink preparation reveals the thick polysaccharide capsule of Cryptococcus neoformans as a clear halo around yeast cells; the organism is urease-positive and phenol oxidase-positive.
- Septate acute-angle hyphae
- Aspergillus species show septate hyphae with acute-angle branching; galactomannan antigen detection in serum supports the diagnosis of invasive aspergillosis.
- Broad nonseptate right-angle hyphae
- Mucorales such as Rhizopus and Mucor show broad, nonseptate hyphae with right-angle branching; they cause mucormycosis in immunocompromised and diabetic patients.
- Dimorphic fungi
- Dimorphic fungi grow as molds at 25°C and as yeasts at 37°C; examples include Histoplasma capsulatum, Blastomyces dermatitidis, Coccidioides immitis, and Sporothrix schenckii.
- Plasmodium falciparum gametocyte
- Plasmodium falciparum gametocytes are banana- or crescent-shaped; the species also shows multiple ring forms and high parasitemia, with few mature trophozoites or schizonts in peripheral blood.
- Entamoeba histolytica trophozoite
- Entamoeba histolytica trophozoites may contain ingested red blood cells; Entamoeba coli trophozoites do not ingest red blood cells and are nonpathogenic.
- Giardia lamblia trophozoite
- Giardia lamblia trophozoites are pear-shaped with two nuclei and falling-leaf motility; oval cysts are the infectious form and are detected in stool.
- Modified acid-fast oocyst
- Cryptosporidium oocysts appear acid-fast with modified acid-fast staining; infection causes watery diarrhea and is transmitted by contaminated water or food.
- Schistosoma haematobium egg
- Schistosoma haematobium eggs have a terminal spine and are found in urine; S. mansoni eggs have a lateral spine, and S. japonicum eggs have a small lateral knob.
- Secondary antibody response
- A secondary immune response produces rapid, high-titer IgG with greater affinity than the primary response, which produces IgM first followed by IgG.
- CH50 assay
- CH50 measures total classical complement pathway activity by lysis of antibody-sensitized sheep red blood cells; AH50 measures alternative pathway activity.
- Anti-dsDNA
- Antibody to double-stranded DNA is highly specific for systemic lupus erythematosus and correlates with lupus nephritis; ANA is the sensitive screening test.
- Rheumatoid factor
- Rheumatoid factor is IgM antibody directed against IgG; it is sensitive but not specific for rheumatoid arthritis, whereas anti-CCP antibody is more specific.
- Nontreponemal syphilis test
- RPR and VDRL are nontreponemal tests used for syphilis screening and titer monitoring; treponemal tests such as FTA-ABS and TPPA confirm infection.
- CD4 count below 200
- A CD4 T-lymphocyte count below 200 cells/µL is an AIDS-defining condition and indicates increased risk for Pneumocystis jirovecii pneumonia and other opportunistic infections.
- Levey-Jennings chart
- A Levey-Jennings chart plots quality control results over time; values within ±2 SD are acceptable, and a value beyond ±3 SD triggers rejection.
- Westgard 1_3s rule
- The 1_3s Westgard rule rejects a run when one control result exceeds the mean plus or minus 3 standard deviations.
- Coefficient of variation
- Coefficient of variation equals standard deviation divided by mean multiplied by 100; it expresses assay imprecision as a percentage.
- Autoclave spore test
- Autoclave sterilization at 121°C and 15 psi for 15 minutes is monitored with Geobacillus stearothermophilus spores as the biological indicator.
- Preanalytical errors
- Preanalytical errors are the largest source of laboratory error and include improper specimen collection, labeling, transport, and handling before analysis.