MLT GlobeDOH exam preparation (Abu Dhabi) – page 14
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
A freezer used for storing sera must be kept at −20 °C. What is this temperature in degrees Fahrenheit?
°F = (°C × 1.8) + 32 = (−20 × 1.8) + 32 = −36 + 32 = −4 °F. −36 °F forgets to add 32.
According to the CLSI order of draw, a collection requires blood culture, light blue, gold (SST), green, lavender and gray tubes. Which tube is drawn immediately before lavender?
CLSI order: blood culture, citrate, serum tubes, heparin, EDTA, then glycolytic inhibitor. So green (heparin) comes just before lavender; gray is last.
During venipuncture, a seated patient becomes pale, sweaty and says she feels faint. The phlebotomist should first:
Stop the draw immediately, remove tourniquet and needle, apply pressure and lower the head or have the patient lie down. Ammonia inhalants are not recommended.
In the classic Westgard multirule procedure, the 1-2s rule is used as:
In the classic multirule scheme, 1-2s is a warning that prompts checking the other rules. Using it alone for rejection causes a high false-rejection rate (about 5% per control).
A glucose result exceeds the upper limit of the analytical measurement range. The appropriate action is to:
Results outside the AMR are unverified. The sample should be diluted using a validated dilution and the result multiplied by the dilution factor, or reported as greater than the limit per policy.
Why is 10% potassium hydroxide (KOH) added to skin scrapings before microscopy for fungi?
KOH digests keratin and host cell debris, clearing the specimen so hyphae and yeasts stand out. It does not stain or fluoresce fungi; calcofluor white is the fluorescent reagent.
Which yeast forms in tissue appear as a large cell with multiple buds attached, described as a 'ship's wheel' or 'mariner's wheel'?
Paracoccidioides produces a mother cell with many narrow-necked daughter buds around it. Blastomyces has a single broad-based bud.
On cornmeal Tween 80 agar, which feature supports identification of Candida albicans?
Terminal chlamydospores on cornmeal agar with Tween 80 are characteristic of C. albicans (and C. dubliniensis). Arthroconidia suggest Trichosporon or Geotrichum.
A skin scraping from a patient with pale scaly patches on the trunk shows short curved hyphae and round yeasts ('spaghetti and meatballs'). Culture requires olive oil overlay. The organism is:
Malassezia causes pityriasis versicolor, shows the spaghetti-and-meatballs pattern, and most species require lipids for growth. Hortaea causes tinea nigra with dark palmar patches.
Three CSF tubes are collected in order. Which is the usual assignment of tubes 1, 2 and 3?
Tube 1 goes to chemistry/serology, tube 2 to microbiology and tube 3 to hematology, because the last tube is least likely to contain blood or skin contaminants from the puncture.
Normal synovial fluid forms a long string (4–6 cm) when dropped from a syringe. This high viscosity is due to:
Hyaluronic acid from synovial cells makes normal joint fluid viscous. Inflammation breaks down or dilutes hyaluronate, giving a short string.
A urine sample left uncovered at room temperature and in light for several hours may give a false-negative result for:
Bilirubin is photo-oxidised to biliverdin on exposure to light, which does not react on the pad. Urobilinogen is also unstable and oxidises to urobilin.
A healthy student gives a urine sample after a football match. The sediment shows 0–2 hyaline casts/LPF and nothing else abnormal. This finding is:
A few hyaline casts can be seen in normal urine, and numbers rise after strenuous exercise, dehydration or heat. Cellular casts, not hyaline casts, point to renal disease.
Forward typing shows group O, but reverse typing gives no reaction with A1 or B cells. The patient has X-linked agammaglobulinemia. What causes the discrepancy?
Hypogammaglobulinemia gives weak or missing reverse reactions (a group I discrepancy). Rouleaux would cause extra positive reactions, not missing ones.
In tube testing, a reaction with many small agglutinates and a turbid reddish background is graded as:
A 1+ reaction shows many small agglutinates in a turbid background. A 4+ reaction is one solid clump with a clear background.
About what proportion of people in most populations are ABH secretors?
Around 80% of people have at least one functional Se (FUT2) gene and secrete ABH substances.
An antibody is usually considered clinically significant when it:
Antibodies active at body temperature can shorten red cell survival. Those reacting only in the cold are usually insignificant.
Antibody screening at the first prenatal visit should be done for:
D-positive women can have anti-c, anti-K and other antibodies that cause HDFN, so every pregnant woman is screened.
Many laboratories omit the immediate-spin and room-temperature phases in the antibody screen mainly because:
Cold-reactive IgM antibodies such as anti-M, anti-P1 and anti-Lea are found in these phases and are rarely significant.
Four-factor prothrombin complex concentrate, used for urgent warfarin reversal, contains factors:
Four-factor PCC contains the vitamin K–dependent factors II, VII, IX and X (plus proteins C and S). These are the factors reduced by warfarin.