ASCP M cheat sheet

Gram-positive cocci in clusters with catalase-positive reaction are staphylococci; coagulase-positive isolates are Staphylococcus aureus.

Gram-positive cocci in chains that are catalase-negative and optochin-sensitive are Streptococcus pneumoniae; they are also bile soluble.

Gram-negative diplococci that are oxidase-positive are Neisseria; N. meningitidis ferments glucose and maltose, while N. gonorrhoeae ferments glucose only.

On MacConkey agar, lactose fermenters such as Escherichia coli form pink colonies; non-lactose fermenters such as Salmonella and Shigella form colorless colonies.

Oxidase test detects cytochrome c oxidase; Pseudomonas aeruginosa is oxidase-positive, while Enterobacterales are oxidase-negative.

Beta-hemolysis is complete RBC lysis, alpha-hemolysis is partial green discoloration, and gamma-hemolysis is no hemolysis.

MRSA is confirmed by cefoxitin disk diffusion or oxacillin MIC; resistance is mediated by mecA or mecC genes encoding altered penicillin-binding protein.

Group A Streptococcus is bacitracin-sensitive and PYR-positive; Group B Streptococcus is hippurate-positive and CAMP-positive.

Nucleic acid amplification tests detect viral DNA or RNA directly and are generally more sensitive than antigen tests or culture for acute viral infection.

Influenza A and B are classified by hemagglutinin and neuraminidase surface proteins; rapid antigen tests have lower sensitivity than molecular assays.

HIV fourth-generation screening detects p24 antigen plus HIV-1/2 antibodies; a reactive result requires confirmation by antibody differentiation or nucleic acid testing.

HBsAg indicates current hepatitis B infection; anti-HBs indicates immunity; anti-HBc IgM indicates acute infection including the window period.

HBeAg indicates active hepatitis B replication and high infectivity; anti-HBe suggests lower replication but does not alone prove resolution.

Anti-HCV is the screening test for hepatitis C; HCV RNA confirms active infection and is used to monitor treatment response.

Cytomegalovirus produces large intranuclear owl's-eye inclusions; pp65 antigenemia and CMV DNA PCR are used for detection and monitoring.

HSV PCR is preferred for diagnosis; Tzanck smear may show multinucleated giant cells but cannot distinguish HSV from VZV.

Germ tube formation in serum identifies Candida albicans and Candida dubliniensis; other Candida species are germ tube-negative.

Cryptococcus neoformans is an encapsulated yeast that is urease-positive and phenol oxidase-positive; India ink shows its capsule.

Aspergillus species show septate hyphae with acute-angle branching; galactomannan antigen supports diagnosis of invasive aspergillosis.

Mucorales show broad, nonseptate hyphae with right-angle branching; they cause mucormycosis in immunocompromised patients.

Dimorphic fungi grow as molds at 25°C and as yeasts at 37°C; examples include Histoplasma, Blastomyces, Coccidioides, and Sporothrix.

Dermatophytes include Trichophyton, Microsporum, and Epidermophyton; they infect keratinized tissue and are cultured on Sabouraud agar.

Malassezia is lipid-dependent and shows spaghetti-and-meatballs morphology on skin scrapings; it causes tinea versicolor.

Candida glabrata is germ tube-negative and forms small yeast cells without pseudohyphae; it is often fluconazole-resistant.

Plasmodium falciparum shows multiple ring forms and banana-shaped gametocytes; mature trophozoites and schizonts are uncommon in peripheral blood.

Plasmodium vivax enlarges infected RBCs and shows Schüffner dots; relapse occurs from hypnozoites in the liver.

Entamoeba histolytica trophozoites may contain ingested RBCs; Entamoeba coli trophozoites do not ingest RBCs.

Giardia lamblia trophozoites are pear-shaped with two nuclei and falling-leaf motility; cysts are oval and infectious.

Cryptosporidium oocysts are acid-fast and detected with modified acid-fast stain; infection causes watery diarrhea.

Strongyloides stercoralis rhabditiform larvae may be found in stool; autoinfection can cause hyperinfection in immunosuppressed patients.

Schistosoma mansoni eggs have a lateral spine, S. haematobium eggs have a terminal spine, and S. japonicum eggs have a small lateral knob.

Enterobius vermicularis is diagnosed with a Scotch tape preparation from the perianal area; eggs are not reliably found in stool.

Primary antibody response produces IgM first, then IgG; secondary response produces rapid, high-titer IgG with greater affinity.

CH50 measures total classical complement pathway activity by lysis of antibody-sensitized sheep RBCs; AH50 measures alternative pathway.

ANA indirect immunofluorescence on HEp-2 cells is a screening test; anti-dsDNA and anti-Sm are more specific for systemic lupus erythematosus.

Rheumatoid factor is IgM antibody against IgG and is sensitive but not specific; anti-CCP is more specific for rheumatoid arthritis.

Nontreponemal tests RPR and VDRL are used for syphilis screening and titer monitoring; treponemal tests FTA-ABS and TPPA confirm infection.

IgA tissue transglutaminase antibody is used for celiac disease; IgA deficiency can cause false-negative results, so total IgA should be checked.

CD4 T-lymphocyte count below 200 cells/µL is an AIDS-defining condition and indicates risk for Pneumocystis jirovecii pneumonia.

Sandwich ELISA captures antigen between capture and detection antibodies; Western blot separates proteins and confirms reactivity by band pattern.

Levey-Jennings charts plot QC results over time; results within ±2 SD are acceptable, and ±3 SD triggers rejection.

Westgard 1_3s rule rejects a run when one control exceeds mean ±3 SD; 2_2s rejects when two consecutive controls exceed ±2 SD.

Coefficient of variation is CV = (SD/mean) × 100 and expresses assay imprecision as a percentage.

Autoclave sterilization uses 121°C, 15 psi, for 15 minutes; Geobacillus stearothermophilus spores are the biological indicator.

Preanalytical errors are the largest source of laboratory error and include collection, labeling, transport, and specimen handling.

Biosafety level 2 covers routine clinical microbiology; BSL-3 is used for Mycobacterium tuberculosis; BSL-4 for Ebola and other risk group 4 agents.

Sensitivity is TP/(TP+FN); specificity is TN/(TN+FP); positive predictive value depends on disease prevalence.

Proficiency testing evaluates laboratory performance against peer groups and is required for CLIA-certified testing.