MLT GlobeQCHP exam preparation (Qatar) – page 11
749 practice MCQs for the QCHP medical laboratory exam. Level: Intermediate.
Anti-smooth muscle antibodies with F-actin specificity are most associated with:
ASMA (anti-F-actin) and ANA are the serologic markers of type 1 autoimmune hepatitis. Type 2 disease is marked by anti-LKM-1, and primary biliary cholangitis by antimitochondrial antibody.
A 40-year-old woman has a firm goitre, fatigue and raised TSH. Which antibody is found in most patients with this likely condition?
Hypothyroidism with goitre suggests Hashimoto thyroiditis, in which anti-TPO antibodies are present in about 90% of patients. TSH receptor stimulating antibodies cause Graves hyperthyroidism, not hypothyroidism.
Antibodies to glutamic acid decarboxylase (GAD65) are most useful to support a diagnosis of:
GAD65 antibodies, with insulin, IA-2 and ZnT8 antibodies, mark autoimmune beta-cell destruction in type 1 diabetes and latent autoimmune diabetes of adults. They are not typical of insulin-resistant type 2 diabetes.
A woman has dry eyes, dry mouth and parotid swelling. Anti-SS-A (Ro) is positive. Which additional antibody is most characteristic of this condition?
Anti-SS-A and anti-SS-B are the classic antibodies of Sjögren disease; anti-SS-B rarely occurs without anti-SS-A. Anti-Scl-70 is associated with diffuse systemic sclerosis.
To identify the allergen responsible for hay fever without skin testing, the laboratory should measure:
In vitro allergen-specific IgE immunoassays identify sensitisation to individual allergens and replace skin prick testing when needed. Total IgG or allergen IgG4 does not identify IgE-mediated allergy.
A group A patient receives group B red cells in error and develops fever, back pain and haemoglobinuria. Which hypersensitivity type is this?
Preformed anti-B binds antigen on transfused red cells, activates complement and causes intravascular lysis – an antibody against a cell-surface antigen, i.e., type II. Type III involves soluble immune complexes.
Kupffer cells are resident macrophages found in the:
Kupffer cells line the hepatic sinusoids. Resident macrophages of the brain are microglia, and in bone they are osteoclasts.
Lysozyme in tears and saliva protects against bacteria by:
Lysozyme breaks the bonds between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, mainly damaging Gram-positive bacteria. Iron binding is the action of lactoferrin.
The T-cell receptor is associated with a signalling complex that is used as a pan-T-cell marker. This complex is:
CD3 transmits the activation signal after the TCR binds peptide–MHC and is present on all mature T cells. CD33 is myeloid and CD41 is a platelet marker.
HLA-B27 is most strongly associated with which disease?
About 90% of patients with ankylosing spondylitis carry HLA-B27. Coeliac disease is linked to HLA-DQ2/DQ8.
The heavy chain of IgA is designated:
Immunoglobulin class is defined by heavy chain: α for IgA, γ for IgG, δ for IgD, ε for IgE and μ for IgM.
Which immunoglobulin class has the highest concentration in normal adult serum?
IgG makes up about 70–75% of serum immunoglobulin (roughly 7–16 g/L). IgA is second in serum but is the main antibody in secretions.
In flow cytometry, side scatter (SSC) of laser light mainly reflects a cell's:
Light scattered at about 90° (side scatter) increases with cytoplasmic granules and nuclear complexity, so granulocytes have high SSC. Cell size is mainly shown by forward scatter.
Fluorescein isothiocyanate (FITC) used in immunofluorescence emits light of which colour?
FITC absorbs blue light (about 495 nm) and emits green light (about 520 nm). Rhodamine and phycoerythrin emit orange-red light.
To confirm that a colony from an anaerobic blood agar plate is an obligate anaerobe, the laboratory should:
In aerotolerance testing, the colony is subcultured both aerobically (chocolate agar in CO2) and anaerobically. Growth only under anaerobic conditions confirms an obligate anaerobe.
A rapid beta-lactamase test on Haemophilus influenzae uses nitrocefin. A positive result is shown by:
Nitrocefin is a chromogenic cephalosporin; when its beta-lactam ring is broken, it changes from yellow to red. Bubbling is the catalase reaction.
A formed (solid) stool is received for Clostridioides difficile toxin testing. The correct action is to:
Testing is limited to unformed stool (taking the shape of the container) to avoid detecting colonised patients without disease. Anaerobic culture does not solve this problem.
A urine is plated with a 0.001 mL calibrated loop. After overnight incubation, 120 colonies of one organism are counted. The colony count is:
With a 0.001 mL loop, multiply the colony count by 1000: 120 × 1000 = 120,000 CFU/mL (1.2 × 10^5). A 0.01 mL loop would use a factor of 100.
Mannitol salt agar is both selective and differential for Staphylococcus aureus because it contains:
The 7.5% salt inhibits most other bacteria, and S. aureus ferments mannitol, turning phenol red yellow. Crystal violet, lactose and neutral red are MacConkey components.
On Hektoen enteric (HE) agar, a typical Salmonella colony appears:
Salmonella does not ferment lactose, sucrose or salicin, so colonies are blue-green, and H2S gives black centres. Salmon-orange colonies are fermenters such as E. coli.