MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 6
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
Why should subcultures and suspensions of Neisseria meningitidis be handled inside a biological safety cabinet?
Laboratory workers exposed to aerosols of N. meningitidis have developed fatal infection. Manipulating isolates in a class II cabinet, and offering vaccination to staff, reduces this risk.
The Haemophilus influenzae type b (Hib) vaccine is directed against which capsular antigen?
The type b capsule is made of polyribosylribitol phosphate, and conjugated PRP is the Hib vaccine antigen. Lipo-oligosaccharide is an outer membrane component, not capsule.
The preferred specimen for laboratory diagnosis of pertussis by culture or PCR is:
Bordetella pertussis attaches to ciliated cells of the nasopharynx, so a posterior nasopharyngeal swab or aspirate is best. Cotton is toxic to the organism and calcium alginate inhibits PCR.
Very mucoid colonies of Pseudomonas aeruginosa from the sputum of a patient with cystic fibrosis are caused by overproduction of:
Mucoid strains overproduce alginate, an exopolysaccharide that forms biofilm and protects the organism in the CF lung. Pyocyanin is a pigment and does not cause mucoid colonies.
On a thin film, 250 of 10,000 red cells counted contain malaria parasites. What is the parasitemia?
Parasitemia = infected RBCs ÷ total RBCs × 100 = 250 ÷ 10,000 × 100 = 2.5%. Count infected cells, not individual parasites, on thin films.
Large cells with 'owl's eye' intranuclear inclusions in a lung biopsy of a transplant patient suggest infection with:
CMV causes cell enlargement (cytomegaly) with large intranuclear inclusions surrounded by a clear halo. Adenovirus inclusions are smudgy and lack this pattern.
Which specimen is generally preferred for detecting respiratory viruses such as SARS-CoV-2 or RSV by PCR?
Nasopharyngeal specimens have high viral loads, and flocked swabs release cells well into transport medium. Formalin and dry tubes damage viral nucleic acid and viability.
Paired sera tested 2 weeks apart show a rise in antibody titer from 1:8 to 1:64. This indicates:
A fourfold or greater rise in titer between acute and convalescent sera shows active infection. A rise from 1:8 to 1:64 is eightfold.
Three CSF tubes are collected in order. Which is the usual assignment of tubes 1, 2 and 3?
Tube 1 goes to chemistry/serology, tube 2 to microbiology and tube 3 to hematology, because the last tube is least likely to contain blood or skin contaminants from the puncture.
The normal adult CSF white cell count and main cell types are:
Adult CSF normally has up to 5 WBCs/µL, mainly lymphocytes with some monocytes. Neonates have higher counts (up to about 30/µL) with more monocytes.
Normal synovial fluid forms a long string (4–6 cm) when dropped from a syringe. This high viscosity is due to:
Hyaluronic acid from synovial cells makes normal joint fluid viscous. Inflammation breaks down or dilutes hyaluronate, giving a short string.
A urine sample left uncovered at room temperature and in light for several hours may give a false-negative result for:
Bilirubin is photo-oxidised to biliverdin on exposure to light, which does not react on the pad. Urobilinogen is also unstable and oxidises to urobilin.
A healthy student gives a urine sample after a football match. The sediment shows 0–2 hyaline casts/LPF and nothing else abnormal. This finding is:
A few hyaline casts can be seen in normal urine, and numbers rise after strenuous exercise, dehydration or heat. Cellular casts, not hyaline casts, point to renal disease.
Forward typing shows group O, but reverse typing gives no reaction with A1 or B cells. The patient has X-linked agammaglobulinemia. What causes the discrepancy?
Hypogammaglobulinemia gives weak or missing reverse reactions (a group I discrepancy). Rouleaux would cause extra positive reactions, not missing ones.
Many transfusion services require ABO typing on two separately collected samples before issuing non-group-O red cells. The main purpose is to:
A second independent sample shows whether the first tube was drawn from the wrong patient. It does not improve detection of weak subgroups.
In tube testing, a reaction with many small agglutinates and a turbid reddish background is graded as:
A 1+ reaction shows many small agglutinates in a turbid background. A 4+ reaction is one solid clump with a clear background.
On average, people of group O have lower plasma levels of:
VWF carries ABH antigens, and group O VWF is cleared faster, so levels are about 25% lower. This must be considered when interpreting VWF results.
About what proportion of people in most populations are ABH secretors?
Around 80% of people have at least one functional Se (FUT2) gene and secrete ABH substances.
An antibody is usually considered clinically significant when it:
Antibodies active at body temperature can shorten red cell survival. Those reacting only in the cold are usually insignificant.
Antibody screening at the first prenatal visit should be done for:
D-positive women can have anti-c, anti-K and other antibodies that cause HDFN, so every pregnant woman is screened.