MLT GlobeDHA exam preparation (Dubai) – page 15
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
The three basic principles for limiting exposure to ionising radiation in the laboratory are:
Radiation dose is reduced by minimising exposure time, increasing distance from the source and using shielding, following the ALARA principle. PPE alone does not stop penetrating radiation.
During routine venipuncture, the needle should enter the vein at an angle of about:
An angle of about 15–30 degrees (bevel up) allows smooth vein entry without passing through the back wall. Steeper angles increase the risk of going through the vein.
Before collecting blood from an inpatient, the phlebotomist must positively identify the patient by:
At least two unique identifiers, checked against the wristband and request, are required. Room numbers are not identifiers, and a yes/no question may be answered wrongly by a confused patient.
A potassium result of 6.9 mmol/L is a critical value. The best practice when reporting it by telephone is to:
Critical values need prompt communication to a responsible licensed caregiver, with read-back of the result and documentation of who received it. Waiting for the clinician to see it in the system may delay urgent care.
A colony on anaerobic blood agar shows an inner zone of complete hemolysis surrounded by an outer zone of partial hemolysis. This double-zone hemolysis is typical of:
C. perfringens shows double-zone hemolysis: the inner complete zone is from theta toxin and the outer partial zone is from alpha toxin.
A suprapubic bladder aspirate from an infant grows 500 CFU/mL of E. coli. How should this be interpreted?
Suprapubic aspiration bypasses the urethra, so any growth of a uropathogen is significant. The 10^5 CFU/mL rule applies to voided midstream specimens.
A tissue biopsy for bacterial culture arrives in 10% formalin. What should the laboratory do?
Formalin kills bacteria, so a fixed specimen cannot give a valid culture result. Tissue for culture should be sent sterile, unfixed, in a small amount of saline.
An organism is inoculated on Simmons citrate agar. After 24 hours the slant has turned deep blue. This means the organism:
Organisms that use citrate as the only carbon source also use ammonium salts, which makes the medium alkaline; bromthymol blue turns from green to blue.
A patient with a damaged mitral valve has had low-grade fever for 6 weeks after a dental extraction. Blood cultures grow alpha-hemolytic, optochin-resistant, bile-insoluble streptococci. The most likely group is:
Viridans streptococci from the mouth enter blood during dental procedures and cause subacute endocarditis on abnormal valves. Optochin resistance and bile insolubility exclude S. pneumoniae.
The Kinyoun acid-fast stain differs from the Ziehl-Neelsen stain because it:
Kinyoun is a 'cold' method: a higher concentration of basic fuchsin and phenol drives the dye into the waxy wall without heating. Auramine is used in fluorochrome staining, not Kinyoun.
The HACEK organisms are clinically important mainly because they are a cause of:
HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella) are oral flora that cause endocarditis and may need longer incubation to grow in blood cultures.
A neutropenic patient develops painless skin nodules that become necrotic ulcers with black centres. This lesion, ecthyma gangrenosum, is classically caused by:
Ecthyma gangrenosum results from P. aeruginosa invading blood vessel walls in the skin, usually in neutropenic patients with bacteremia.
For enrichment of Vibrio cholerae from stool, the specimen is inoculated into:
Alkaline peptone water (pH about 8.4) favours vibrios, which tolerate alkaline pH, and suppresses most other stool flora. It is subcultured to TCBS after 6–8 hours.
A chronic knee effusion from a patient with long-standing rheumatoid arthritis shows large, flat, rectangular plates with notched corners. These are:
Notched rectangular plates are typical of cholesterol, seen in chronic effusions. Calcium oxalate crystals are envelope- or dumbbell-shaped and occur in renal dialysis patients.
Which reagent strip technique is correct?
The strip is dipped briefly so all pads are wet, and excess is removed to prevent run-over. Prolonged dipping leaches reagents from the pads.
Urinary casts are best screened and reported under:
Casts are scanned under low power with subdued light, because hyaline casts have a low refractive index and are easily missed in bright light. They are reported as the average per LPF.
Budding yeast with branching pseudohyphae is seen in urine from a woman with poorly controlled diabetes. The organism is most likely:
Candida produces budding yeast and pseudohyphae and is common in diabetic urine, where glucose supports growth. Cryptococcus does not form pseudohyphae.
Which viral infection, common in South Asia, typically causes a marked fall in the platelet count?
Dengue commonly causes marked thrombocytopenia, and serial platelet counts are used to monitor patients.
Which coagulation factor belongs only to the extrinsic pathway?
Factor VII, activated with tissue factor, is unique to the extrinsic pathway, which is measured by the PT. Factors VIII and IX are intrinsic, and X is in the common pathway.
Cold autoimmune hemolytic anemia is usually caused by an autoantibody of which class?
Cold agglutinins are usually IgM, which bind red cells in the cold and activate complement. Warm AIHA is usually IgG.