MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 11
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
A single blood culture bottle grows Staphylococcus aureus. How should this result be regarded?
S. aureus is rarely a blood culture contaminant, so even one positive bottle is treated as true bacteremia and reported promptly. Coagulase-negative staphylococci, not S. aureus, are the common contaminants.
Protein A of Staphylococcus aureus helps the organism avoid phagocytosis by binding:
Protein A binds the Fc region of IgG, so antibodies attach in the wrong orientation and cannot act as opsonins. Binding of fibrinogen is the role of clumping factor.
Malachite green is included in Löwenstein-Jensen medium to:
Malachite green is a selective dye that suppresses many contaminating bacteria. The egg base is solidified by inspissation, not by the dye.
Identification and drug-susceptibility testing on a growing culture of Mycobacterium tuberculosis should be performed under:
Manipulating cultures produces aerosols with very high numbers of bacilli, so BSL-3 containment is required. A clean-air bench protects the product, not the worker.
A surgeon sends only a dry swab from a deep abscess for mycobacterial culture. Why are swabs discouraged for this test?
Swabs hold only a small volume, and waxy mycobacteria stick to the fibres, lowering recovery. Tissue or aspirated fluid is preferred.
A false-positive oxidase test is most likely when colonies are picked with:
Iron in nichrome wire can oxidize the oxidase reagent and give a false-positive colour. Platinum, wood or plastic tools are recommended.
The reference range for total protein in adult lumbar CSF is approximately:
Normal lumbar CSF protein is about 15–45 mg/dL, much lower than plasma protein (60–80 g/L). Newborns have higher values.
The total volume of CSF in an adult and its approximate daily production are:
Adults have about 90–150 mL of CSF, produced mainly by the choroid plexus at about 500 mL per day, so it is replaced several times daily.
CSF cell counts should be performed within about 1 hour of collection because:
Cells, especially neutrophils, start to disintegrate in CSF within about an hour, falsely lowering counts. Glucose loss affects chemistry, not the cell count.
What is the usual upper limit of the WBC count in normal synovial fluid?
Normal synovial fluid has fewer than about 200 WBCs/µL, mostly mononuclear cells. Counts of 2,000–50,000/µL suggest inflammatory arthritis.
During arthrocentesis, the first tube is bloody but later tubes become clearer. This pattern most likely indicates:
Blood from needle injury is uneven and decreases as aspiration continues. True joint haemorrhage gives uniformly bloody fluid in all tubes.
Amniotic fluid sent for bilirubin (ΔA450) measurement in suspected haemolytic disease of the fetus should be:
Bilirubin is broken down by light, which gives falsely low results. The specimen must be shielded from light immediately after collection.
A patient taking high-dose vitamin C has a guaiac fecal occult blood test. What effect is expected?
Vitamin C is a reducing agent that blocks oxidation of guaiac, so bleeding may be missed. Red meat and some vegetables with peroxidase activity cause false positives.
An infant has sweat chloride of 72 mmol/L on two separate tests. The best interpretation is:
Sweat chloride of 60 mmol/L or more supports cystic fibrosis; 30–59 mmol/L is intermediate and below 30 is unlikely. Repeat positive tests with clinical findings confirm the diagnosis.
The nitrite pad of a reagent strip is based on which reaction?
Nitrite reacts with an aromatic amine to form a diazonium salt, which couples with a second compound to give a pink colour. Peroxidase activity is the basis of the blood pad.
The reagent strip pH pad uses a double indicator system of:
Methyl red and bromthymol blue give a colour range from orange to blue across pH 5 to 9. Tetrabromphenol blue is the protein pad indicator.
Many round urothelial (transitional) epithelial cells with normal morphology are seen in a urine collected just after bladder catheterisation. This finding is most likely:
Catheterisation scrapes cells from the urothelium, so increased normal transitional cells are expected. Malignancy is suspected only when cells show abnormal nuclear features.
Large, flat urinary epithelial cells with abundant cytoplasm and a small central nucleus are most often:
These are squamous cells, the largest cells in sediment, and in large numbers suggest a poorly collected specimen. Renal tubular cells are smaller with an eccentric nucleus.
Which hemoglobin value lies within the usual reference interval for a healthy adult man?
Adult male hemoglobin is roughly 13–17 g/dL, so 15.0 g/dL is well inside the range. 9.5 and 11.0 g/dL indicate anemia, and 21.0 g/dL suggests polycythemia.
Which plasma protein carries iron from the gut and storage sites to developing red cells in the marrow?
Transferrin is the iron transport protein of plasma and delivers iron to erythroblasts through the transferrin receptor. Ferritin is the storage form, and haptoglobin binds free hemoglobin.