MLT GlobeDOH exam preparation (Abu Dhabi) – page 30
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
A clinician wants a test to confirm (rule in) a disease with the fewest false-positive results. The most important test characteristic is high:
High specificity means few false positives, so a positive result reliably rules in disease. High sensitivity (few false negatives) is best for ruling out disease.
A comparison of a new method (y) with the current method (x) gives the regression equation y = 1.00x + 8 mg/dL. This shows:
A y-intercept different from zero with a slope of 1.00 means the new method reads a fixed amount higher at all levels: constant error. A slope different from 1.00 would indicate proportional error.
Calcofluor white is useful for direct fungal detection because it:
Calcofluor white binds beta-linked polysaccharides such as chitin and cellulose in fungal walls and fluoresces blue-white or apple-green depending on filters. A clear halo describes India ink with Cryptococcus.
A yeast isolate from a patient in an ICU is resistant to fluconazole, is misidentified by some biochemical systems, and spreads between patients on surfaces. Which organism is of greatest concern?
Candida auris is often multidrug resistant, persists on surfaces, causes healthcare outbreaks and is misidentified by older biochemical methods. MALDI-TOF with an updated database or molecular methods is recommended.
Which method is recommended for reliable identification of Candida auris?
MALDI-TOF MS with a validated, updated library or DNA sequencing reliably identifies C. auris. It is germ tube negative and gives no characteristic colony on plain SDA, so these cannot identify it.
Which serum or CSF test is most sensitive and specific for diagnosing cryptococcal meningitis?
Cryptococcal antigen (CrAg) lateral flow assay detects capsular glucuronoxylomannan with very high sensitivity. India ink misses many cases, and Cryptococcus has little beta-D-glucan.
A mold culture at 25 °C shows large, thick-walled tuberculate macroconidia and small microconidia. This suggests:
Tuberculate (knobby) macroconidia are characteristic of the mold phase of Histoplasma capsulatum. Sepedonium species look similar, so conversion or molecular confirmation is needed.
Handling a mold culture of Coccidioides immitis on an open bench is dangerous mainly because it produces:
The mold phase forms alternating barrel-shaped arthroconidia that become airborne and cause laboratory infections. Suspected cultures must be handled in a biosafety cabinet under BSL-3 conditions.
A blue-green mold grows rapidly at 45 °C. Microscopy shows uniseriate phialides covering only the upper part of a club-shaped vesicle. The most likely species is:
A. fumigatus has uniseriate phialides on the upper two-thirds of the vesicle, bluish-green colonies and tolerates high temperature. A. niger has black colonies with biseriate phialides covering the whole vesicle.
When tissue is submitted for suspected mucormycosis, the laboratory should mince it rather than grind it because:
Pauciseptate hyphae of Mucorales are easily destroyed by homogenization, which lowers culture recovery. Gentle mincing of tissue keeps hyphae viable.
CSF from a lumbar puncture is bloody in tube 1 and becomes clearer in tubes 2 and 3. The supernatant is clear and colourless. This most suggests:
A falling red cell count from tube 1 to 3 with a clear supernatant indicates blood introduced by the needle. Subarachnoid hemorrhage gives evenly bloody tubes and, after some hours, xanthochromia.
A cytocentrifuge CSF slide from a child being treated for acute lymphoblastic leukemia shows large cells with fine chromatin and nucleoli. This indicates:
Blasts in CSF indicate CNS leukemia, which changes treatment. Choroid plexus and ependymal cells appear in clusters and have uniform, mature nuclei.
Synovial fluid from a painful big toe contains needle-shaped crystals. With a red compensator, they are yellow when parallel to the slow axis. These crystals are:
Monosodium urate crystals of gout are needle-shaped and strongly negatively birefringent: yellow when parallel to the slow axis. CPPD crystals appear blue in that position.
A lymphocytic pleural exudate from a young patient in a high-prevalence country has markedly raised adenosine deaminase (ADA). This most suggests:
High pleural ADA with lymphocyte predominance strongly supports tuberculous pleurisy, especially where TB is common. Heart failure causes a transudate with low ADA.
A patient with cirrhotic ascites develops fever. Which ascitic fluid finding is diagnostic of spontaneous bacterial peritonitis?
An ascitic neutrophil count of at least 250 cells/µL establishes spontaneous bacterial peritonitis even before culture results. SAAG reflects portal hypertension, not infection.
A patient with chronic diarrhoea, weight loss and bulky stools has fecal elastase-1 of 80 µg/g stool. This result suggests:
Fecal elastase-1 below about 200 µg/g (and especially below 100 µg/g) indicates exocrine pancreatic insufficiency. Elastase is stable in the gut, so it reflects pancreatic output.
Albumin-to-creatinine ratio (ACR) is preferred to a routine dipstick for early diabetic kidney disease because:
Routine strips detect about 150–300 mg/L protein, missing moderately increased albuminuria. ACR corrects for urine concentration; KDIGO defines A2 as 30–300 mg/g (3–30 mg/mmol).
Yellow-brown clumped needles are seen in urine with a positive dipstick bilirubin in a patient with hepatitis. These crystals are:
Bilirubin crystals appear as clumped yellow-brown needles or granules and match a positive bilirubin pad. Sulfonamide crystals are usually linked to drug therapy and a negative bilirubin test.
For a neonate younger than 4 months, repeat ABO/D typing during the same hospital admission is:
Infants under 4 months rarely make new antibodies, so one ABO/D type per admission is enough. Reverse typing is not done because antibodies are maternal.
A single unit of cryoprecipitate is thawed and NOT pooled. It is kept at 20–24 °C. It must be transfused within:
Thawed single (or closed-system pooled) cryoprecipitate expires 6 hours after thawing at room temperature. The 4-hour limit applies when pooling is done in an open system.