MLT GlobeDHA exam preparation (Dubai) – page 32
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
An antibody reacts only at the AHG phase with Fy(a+) panel cells and stops reacting when the cells are treated with ficin. The most likely specificity is:
Fya is destroyed by ficin, so anti-Fya reactivity disappears. Kidd, Rh and Lewis antibodies are enhanced by enzyme treatment, not abolished.
Malaria can be transmitted by red cell transfusion mainly because Plasmodium parasites:
Malaria parasites live inside red cells and can survive refrigerated storage, so any red-cell-containing component can transmit them. This is why donors are screened in endemic countries.
After stopping a transfusion because of a suspected reaction, the IV line should be:
The venous access is kept open with normal saline (through a new giving set) so fluids and drugs can be given if the patient gets worse.
Bilirubin rises quickly after birth in HDFN mainly because:
Before birth the placenta clears bilirubin to the mother. After birth the immature liver has little glucuronyl transferase activity, so bilirubin from ongoing hemolysis builds up.
A patient has total protein 9.5 g/dL (95 g/L) and albumin 3.0 g/dL (30 g/L). Which protein group is most likely increased?
Globulin = total protein − albumin = 6.5 g/dL, well above the usual 2.0–3.5 g/dL. A high total protein with normal-to-low albumin points to raised globulins, for example immunoglobulins.
A malnourished child has generalised edema. Which serum finding best explains the edema?
Albumin provides most of the plasma oncotic pressure. When albumin is low, fluid leaks from vessels into tissues, producing edema, as in kwashiorkor.
A patient's antiepileptic drug level is repeatedly below the therapeutic range despite a correct prescribed dose. What is the most common cause?
Poor adherence is the most frequent reason for unexpectedly low drug levels. Kidney failure usually raises levels, and a peak sample would give a higher, not lower, result.
A woman has dysuria and frequency without fever or flank pain. Urine shows many white cells and bacteria but no casts. This is most consistent with:
Pyuria and bacteriuria without white cell casts or systemic signs suggest infection of the bladder. White cell casts would point to kidney involvement (pyelonephritis).
Which quality control strain is routinely used by CLSI for disk diffusion testing of Enterobacterales?
E. coli ATCC 25922 is the standard QC strain for disk diffusion of Enterobacterales; S. aureus ATCC 29213 is used for MIC testing of staphylococci.
The slide coagulase test detects which staphylococcal product?
Clumping factor on the cell surface makes cells clump in plasma on a slide; the tube test detects free coagulase.
A TSI slant shows acid slant, acid butt with gas and no blackening. Which organism fits best?
E. coli ferments lactose/sucrose (A/A) with gas and no H2S; Shigella gives K/A, while Salmonella and Proteus give K/A with H2S.
Which CSF pattern is typical of acute bacterial meningitis?
Bacteria and neutrophils consume glucose and inflammation raises protein; viral meningitis usually shows lymphocytes with normal glucose.
Obligate anaerobes are intrinsically resistant to aminoglycosides such as gentamicin because:
Aminoglycoside entry depends on an oxygen-driven electron transport system that anaerobes lack; beta-lactamase does not affect aminoglycosides.
Plasmodium vivax preferentially invades which red cells?
P. vivax and P. ovale prefer reticulocytes, which limits their parasitaemia; P. falciparum invades red cells of all ages.
Alveolar hydatid disease, which grows like an invasive tumour in the liver, is caused by:
E. multilocularis, with foxes as main definitive hosts, forms infiltrating multivesicular (alveolar) cysts; E. granulosus forms unilocular cysts.
Which dermatophyte is the most common cause of tinea pedis and fungal nail infections worldwide?
T. rubrum is the leading cause of chronic foot and nail infection; M. canis mainly causes scalp and body ringworm from pets.
On dermatophyte test medium (DTM), a dermatophyte is suggested by:
Dermatophytes use protein and make the medium alkaline, turning the phenol red indicator red.
For rapid electron microscopy of viruses in a stool or fluid sample, particles are commonly 'negatively stained' with:
Heavy-metal salts such as phosphotungstic acid surround the particles, so they stand out light against a dark background.
A biological safety cabinet should be certified for correct airflow and filter integrity:
Certification is needed at installation, after moving or filter changes, and at least yearly.
The positive predictive value of a test is the probability that:
PPV = true positives ÷ all positives; it depends on disease prevalence as well as test performance.