MLT GlobeDHA exam preparation (Dubai) – page 31
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
A cell culture inoculated with a nasopharyngeal specimen from an infant with bronchiolitis shows large multinucleated cells (syncytia) in HEp-2 cells. The most likely virus is:
RSV causes cell fusion and syncytia in continuous cell lines such as HEp-2. Adenovirus produces rounded, grape-like clusters instead.
An unvaccinated child has fever, cough, conjunctivitis, a spreading maculopapular rash and small white spots on the buccal mucosa. Which test best confirms the diagnosis?
Koplik spots with the classic prodrome suggest measles, confirmed by measles IgM and/or RT-PCR of respiratory or urine specimens. Rubella avidity helps date rubella infection, not measles.
A patient with advanced HIV has progressive weakness and confusion. MRI shows white matter lesions without mass effect. Which CSF test best supports the likely diagnosis?
Progressive multifocal leukoencephalopathy is caused by JC virus infecting oligodendrocytes and is supported by JC virus DNA in CSF. Toxoplasma usually causes ring-enhancing mass lesions.
A student has painful swelling of the parotid glands. Which specimen is best for RT-PCR confirmation of the likely virus?
Mumps virus is shed in saliva, so a buccal swab near Stensen's duct after gland massage gives the best yield, ideally within a few days of swelling.
CSF protein electrophoresis shows several discrete bands in the gamma region that are absent from the patient's paired serum. This finding most supports:
Oligoclonal bands found in CSF but not serum show intrathecal IgG synthesis, as in multiple sclerosis. Bands present in both CSF and serum reflect systemic immune activity.
A patient has severe chest pain after repeated vomiting. Left pleural fluid has a very high amylase, a low pH and food particles. The most likely cause is:
Salivary amylase and gastric contents leak into the pleural space through an oesophageal tear. Pancreatitis also raises pleural amylase, but food particles point to oesophageal rupture.
Bloody pleural fluid has a haematocrit of 22%, and the blood haematocrit is 38%. This most likely indicates:
A fluid haematocrit greater than 50% of the blood haematocrit (here 58%) defines a haemothorax. A traumatic tap gives much less blood, and its amount falls as the tap continues.
Pleural fluid contains more than 10% eosinophils. Which is the most common cause?
Pneumothorax and haemothorax are the most frequent causes of pleural eosinophilia; allergy, parasites and some drugs are others. Tuberculous effusions are usually lymphocytic.
A semen sample is still a thick gel 90 minutes after collection at body temperature. Deficient secretion from which gland most likely explains this?
Semen coagulates due to seminal vesicle proteins and liquefies through prostatic proteases such as PSA. Liquefaction not complete by 60 minutes suggests prostatic dysfunction.
Using strict (Tygerberg) criteria, what is the WHO 2021 lower reference limit for sperm with normal morphology?
The WHO 2021 5th centile for normal forms by strict (Tygerberg) criteria is 4%. 54% is the lower limit for vitality, 30% for progressive motility, and 14% was Kruger's older strict-criteria prognostic threshold, not the WHO reference limit.
A 25-year-old with chronic diarrhoea has fecal calprotectin of 450 µg/g. This result most supports:
Calprotectin comes from neutrophils in the gut wall, so high levels indicate mucosal inflammation such as IBD. Irritable bowel syndrome usually gives normal calprotectin.
A strip is held horizontally too long after dipping, and the pH pad reads falsely low. The most likely cause is:
If excess urine is not removed, the acid buffer of the protein pad can run over onto the pH pad and lower the reading. Loss of CO2 or bacterial growth tends to raise pH.
A patient receiving high-dose trimethoprim-sulfamethoxazole has brown sheaves of needles and fan-like crystals in acidic urine. They are most likely:
Sulfonamide crystals form sheaves, fans or rosettes in acidic urine of patients on sulfa drugs, especially when poorly hydrated. Medication history helps separate them from tyrosine in liver disease.
A cellular cast slowly degenerates as it stays in the tubule. Which sequence of cast appearance is expected?
Cells in a cast break down into coarse, then fine granules, and long stasis gives a homogeneous waxy cast. Waxy casts therefore imply prolonged urine stasis.
Spherocytes form mainly because red cells:
When membrane is lost (for example through a defect in HS or removal of antibody-coated membrane by macrophages), the cell takes the shape with the least surface area for its volume, which is a sphere. Excess membrane gives target cells.
Cabot rings, seen in some severe anemias, are thought to be remnants of:
Cabot rings are thin ring or figure-of-eight inclusions thought to come from microtubules of the mitotic spindle. Ribosomal RNA gives basophilic stippling and denatured hemoglobin forms Heinz bodies.
Clot retraction depends mainly on:
Platelets contract through their actin-myosin system and pull on fibrin through GP IIb/IIIa. Clot retraction is poor in thrombocytopenia and Glanzmann thrombasthenia.
Activated protein C needs which cofactor to inactivate factors Va and VIIIa?
Protein S is the cofactor of activated protein C. Thrombomodulin helps thrombin activate protein C in the first place but is not the APC cofactor.
Hb Bart's is a tetramer made of four:
When alpha chains are severely lacking in fetal life, the extra gamma chains form γ4 (Hb Bart's). In adults the extra beta chains form β4 (HbH).
In the cyanmethemoglobin method, which reagent oxidizes hemoglobin to methemoglobin?
In Drabkin's reagent, potassium ferricyanide oxidizes hemoglobin to methemoglobin, and potassium cyanide then converts it to stable cyanmethemoglobin, read at 540 nm.