MLT GlobeDHA exam preparation (Dubai) – page 26
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
A thick film from a patient in Central America shows a trypomastigote with a large posterior kinetoplast, often curved into a 'C' shape. The organism is:
T. cruzi trypomastigotes have a large kinetoplast and a typical C shape; it causes Chagas disease in the Americas. African trypanosomes have a small kinetoplast.
A cyst in an iodine wet mount has a single nucleus and a large, sharply outlined glycogen vacuole that stains brown. It is:
Iodamoeba cysts have one nucleus and a prominent glycogen mass that stains dark brown with iodine. Endolimax cysts have four small nuclei without a large vacuole.
A round egg about 35 µm with a thick radially striated shell containing a six-hooked oncosphere is seen. The correct report is:
Eggs of T. solium and T. saginata look identical, so they are reported as Taenia species. Species identification requires the scolex or gravid proglottids, or molecular testing.
HBsAg has been positive for 8 months. Total anti-HBc is positive, IgM anti-HBc is negative and anti-HBs is negative. This indicates:
HBsAg persisting beyond 6 months defines chronic infection. Absent IgM anti-HBc argues against acute infection.
Which hepatitis virus spread by the fecal–oral route causes a high death rate in pregnant women, especially in the third trimester?
HEV genotypes 1 and 2, spread by contaminated water, can cause fulminant hepatitis in pregnancy. HAV is also fecal–oral but does not show this high mortality in pregnancy.
How is HIV infection diagnosed in a 2-month-old infant born to an HIV-positive mother?
Maternal IgG antibodies cross the placenta and may last up to 18 months, so antibody tests cannot diagnose infant infection. Virologic tests (NAT) are required.
A Tzanck smear from a vesicle shows multinucleated giant cells. Which statement is correct?
HSV-1, HSV-2 and VZV all produce multinucleated giant cells with nuclear molding. PCR or specific antigen tests are needed to identify the virus.
A 3-year-old has fever, pharyngitis and atypical lymphocytes, but the heterophile antibody test is negative. Which test is best next?
Young children often do not make heterophile antibodies during EBV infection. EBV-specific VCA IgM shows acute infection.
EBV serology shows VCA IgG positive, VCA IgM negative and EBNA IgG positive. This indicates:
Antibody to EBNA appears weeks to months after infection and persists for life. With negative VCA IgM, the pattern shows past infection.
A viral specimen in transport medium cannot be tested for 5 days. How should it be stored?
Specimens can be held at 2–8 °C for up to about 72 hours. For longer delays, freezing at −70 °C preserves viruses; −20 °C and freeze–thaw cycles reduce recovery.
What is the purpose of an internal control in a viral PCR assay?
The internal control is amplified in every sample. If it fails, a negative result is invalid because inhibitors or poor extraction may have caused it.
A patient has had fever, headache and muscle pain for 2 days after travel to a dengue area. Which test is most useful now?
During the first 5 days of fever, viremia and NS1 antigen are high while IgM is usually not yet present. IgM becomes useful after about day 5.
Serum albumin is 3.0 g/dL and ascitic fluid albumin is 1.2 g/dL. The serum–ascites albumin gradient and its meaning are:
SAAG = serum albumin − ascitic albumin = 3.0 − 1.2 = 1.8 g/dL. A gradient of 1.1 g/dL or more indicates portal hypertension, such as cirrhosis.
Which is an advantage of the fecal immunochemical test (FIT) over the guaiac fecal occult blood test?
FIT uses antibodies to human globin, so diet (red meat, peroxidase-rich vegetables) does not cause false positives. Globin is digested in the upper GI tract, so FIT detects mainly lower GI bleeding.
A highly alkaline urine (pH 9) may cause which error on the reagent strip protein pad?
Highly alkaline or heavily buffered urine overcomes the pad buffer and changes the indicator colour without protein, giving a false-positive result.
High levels of ascorbic acid in urine can cause false-negative results on which pads?
Ascorbic acid is a strong reducing agent that removes hydrogen peroxide and inhibits the peroxidase-type reactions on the blood and glucose pads. It can also affect bilirubin, nitrite and leukocyte esterase.
A persistently high urine pH (above 8.0) in a fresh specimen from a patient with a UTI suggests infection with:
Urease splits urea into ammonia, making urine alkaline and favouring struvite (triple phosphate) stones. An old unrefrigerated specimen can give the same false result.
A patient with heavy proteinuria has casts containing highly refractile droplets that show 'Maltese cross' patterns under polarized light. These are:
Fatty casts contain cholesterol-rich lipid droplets that form Maltese crosses under polarized light, typical of nephrotic syndrome. Waxy casts are homogeneous and do not polarize this way.
A hospitalized patient develops acute kidney injury after hypotension. Urine sediment shows many 'muddy brown' coarse granular casts and renal tubular epithelial cells. This suggests:
Muddy brown granular casts and tubular cells reflect injured, sloughing tubular epithelium in acute tubular necrosis. Prerenal azotemia usually has a bland sediment with only hyaline casts.
Colourless hexagonal plates are seen in acidic urine from a child with kidney stones. Which test confirms their identity?
Hexagonal crystals suggest cystine (cystinuria); the cyanide–nitroprusside test turns red-purple with cystine. Uric acid can form similar-looking plates, so confirmation is important.