MLT GlobeMOH exam preparation (UAE) – page 15
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A technologist is splashed in the eyes with a corrosive reagent. The immediate action is to:
Eyes should be flushed with water at an eyewash station for at least 15 minutes, holding lids open, then medical evaluation follows. Neutralizing agents can cause further injury.
A sharps container in the phlebotomy area should be closed and replaced when it is:
Sharps containers are replaced at about 3/4 full (or at the fill line) to prevent needles protruding and injuries from overfilling.
A 3.2% sodium citrate tube for PT and aPTT is received only half full. What effect is expected if it is tested?
The correct blood-to-citrate ratio is 9:1. Underfilling leaves excess citrate, which binds the added calcium in the test and falsely prolongs PT and aPTT.
A patient has an IV infusion running in the left forearm. The right arm has suitable veins. Where should blood be collected?
Blood should be drawn from the arm without the IV to avoid dilution and contamination by IV fluid. Drawing above an IV site is never acceptable.
A neonatal bilirubin specimen is collected. Which special handling is required?
Bilirubin is broken down by light, which can lower the result by a significant amount within an hour. Use an amber tube or wrap it in foil.
A potassium control has a mean of 4.0 mmol/L and an SD of 0.1 mmol/L. The ±2 SD acceptable range is:
±2 SD = 4.0 ± (2 × 0.1) = 3.8 to 4.2 mmol/L, which includes about 95% of expected values. 3.7–4.3 is the ±3 SD range.
A gardener develops nodules that follow the lymphatic vessels up the arm after a thorn injury. Culture at 25 °C shows thin hyphae with conidia arranged like flower petals. The organism is:
Lymphocutaneous spread after a plant injury with a mold showing rosette ('flowerette') conidia is typical of Sporothrix. It converts to cigar-shaped yeasts at 37 °C.
Hair infected with Microsporum canis viewed under a Wood's lamp typically shows:
Most Microsporum species causing ectothrix infection fluoresce yellow-green under Wood's light. Trichophyton tonsurans (endothrix) does not fluoresce; coral-red fluorescence suggests erythrasma.
A mold from an ear swab has a white surface that turns black ('salt and pepper'), with a pale reverse. Microscopy shows large round vesicles fully covered by biseriate phialides. The organism is:
Black conidial heads with a pale reverse and a radiate head covered by biseriate phialides are typical of A. niger, a common cause of otomycosis. Dematiaceous molds such as Alternaria have a dark reverse.
Branching conidiophores with metulae and phialides bearing chains of conidia, forming a 'brush-like' structure, describe:
The penicillus (brush) of Penicillium consists of branched metulae and phialides without a vesicle. Aspergillus conidiophores end in a swollen vesicle.
A diabetic patient in ketoacidosis has necrotic tissue in the nasal cavity. Histology shows broad, ribbon-like, rarely septate hyphae with right-angle branching. The likely order is:
Rhino-orbital-cerebral mucormycosis in ketoacidosis shows wide, pauciseptate, ribbon-like hyphae branching at wide angles. Aspergillus hyphae are narrow, regularly septate and branch at acute angles.
Pneumocystis jirovecii in bronchoalveolar lavage is best demonstrated by:
Pneumocystis cannot be cultured routinely; cysts are shown with immunofluorescence, methenamine silver or calcofluor, and PCR is also used. Culture on SDA gives no growth.
Routine fungal cultures for suspected dimorphic pathogens should be held before reporting 'no growth' for at least:
Dimorphic fungi such as Histoplasma and Blastomyces may take several weeks to grow, so cultures are held for about 4 weeks. Shorter holding times risk false-negative reports.
Which condition most typically produces a pleural transudate?
Transudates result from changes in hydrostatic or oncotic pressure, as in heart failure, cirrhosis or nephrotic syndrome. Infection and cancer damage the membrane and give exudates.
Which instruction is correct for a man collecting a semen sample for fertility testing?
WHO advises 2–7 days of abstinence, collection into a clean non-toxic container, and delivery within about an hour at body-near temperature. Ordinary condoms contain spermicides that affect motility.
The glucose pad on a reagent strip uses which enzyme system?
Glucose oxidase produces hydrogen peroxide, which peroxidase uses to oxidise a chromogen. The reaction is specific for glucose.
The reagent strip blood pad detects hemoglobin through:
Heme has peroxidase-like activity that breaks down the pad's hydrogen peroxide and oxidises a chromogen. Strong oxidising contaminants such as bleach can therefore cause false-positive results.
Yellow-brown, rhombic or rosette-shaped crystals that polarize strongly are seen in a urine with pH 5.5. They are most likely:
Uric acid crystals form in acidic urine, are yellow to red-brown, take rhombic, barrel or rosette shapes, and are strongly birefringent. Triple phosphate and calcium carbonate form in alkaline urine.
Colourless, prism-shaped 'coffin-lid' crystals in alkaline urine from a patient with a Proteus infection are:
Urease-producing bacteria such as Proteus make urine alkaline and promote struvite (triple phosphate) crystals and stones. Cystine forms hexagonal plates in acidic urine.
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.