Medical laboratory technician interviews test your knowledge of sample collection, haematology, biochemistry and microbiology techniques, lab safety and quality control. These questions suit DMLT and BMLT graduates applying to hospital and diagnostic labs.
These answers are for interview preparation and follow standard teaching. They are not clinical guidance; always follow current protocols and your institution's policies.
Fundamentals, definitions and simple scenarios. Good for freshers and warm-ups.
A common recommended order is: blood culture bottles, sodium citrate (light blue), serum tubes with or without clot activator or gel (red or gold), heparin (green), EDTA (lavender), then fluoride oxalate (grey). Following the order prevents additives being carried from one tube to the next, which can give wrong results; for example, EDTA contamination falsely raises potassium and lowers calcium.
EDTA (the lavender-top tube). It prevents clotting by binding calcium, and it preserves the shape and size of blood cells well, which is essential for accurate cell counts and smear examination. The tube must be filled to the correct volume and mixed gently by inverting it several times so the blood does not clot.
Roughly 13 to 17 g/dL in adult men and 12 to 15 g/dL in adult women, although exact reference ranges vary between laboratories and methods, so the lab's own range is always printed on the report. Values below the range indicate anaemia; values are also affected by altitude, pregnancy and hydration.
Under the Bio-Medical Waste Management Rules, 2016: yellow bags for infectious waste such as soiled dressings, human and anatomical waste and discarded medicines; red bags for contaminated recyclable plastic such as tubing, bottles and gloves; a white translucent puncture-proof container for sharps such as needles and blades; and blue boxes or containers for glassware. Waste is segregated at the point it is generated.
Applied problems, trade-offs and questions about your own projects.
Serum is the liquid left after blood has clotted, so it contains no fibrinogen or other clotting factors; it is collected in plain or clot-activator tubes. Plasma is the liquid part of blood collected with an anticoagulant, so it still contains fibrinogen and clotting factors. Many biochemistry tests use serum, while coagulation tests need citrated plasma.
Internal quality control runs control samples of known values with patient samples, plots them on Levey-Jennings charts and applies Westgard rules to decide whether a run can be accepted. External quality assessment, or proficiency testing, compares the lab's results with other labs. With regular calibration, equipment maintenance and documented procedures, this supports accreditation such as NABL under ISO 15189.
Apply crystal violet, then Gram's iodine as a mordant, then decolourise with alcohol or acetone, and counterstain with safranin. Gram-positive bacteria, with their thick peptidoglycan wall, keep the crystal violet and appear purple. Gram-negative bacteria lose it during decolourisation and take up the safranin, appearing pink or red. Decolourisation time is the most critical step.
Causes include a very fine needle, drawing too forcefully, shaking tubes vigorously, a tourniquet left on too long, and delays or temperature extremes before processing. When red cells burst they release their contents, falsely raising potassium, LDH, AST and some other results, and can interfere with test methods. A significantly haemolysed sample should usually be rejected and recollected.
System design, deep internals, leadership and tough follow-ups.
I first make sure the result is genuine: check the sample identity and quality, and repeat the test if the protocol requires it. Then I report it immediately to the responsible doctor or nurse by phone, as per the lab's critical value policy, and ask them to read back the result to confirm. I document the time, the result and the name of the person informed.
Pre-analytical errors happen before the sample is tested, and they make up most laboratory errors. Examples are wrong patient identification, wrong tube, haemolysed or clotted samples, too little sample, delays in transport and wrong storage temperature. They are reduced with two patient identifiers, labelling tubes at the bedside, barcodes, clear collection procedures and training, and rejection criteria for unsuitable samples.
ELISA (enzyme-linked immunosorbent assay) uses the specific binding of an antigen and an antibody. An enzyme linked to an antibody converts a substrate into a coloured product, and the colour intensity, measured by a reader, is proportional to the amount of the target substance. The main types are direct, indirect, sandwich and competitive ELISA. It is used for tests such as HIV, hepatitis B and C screening, and hormone levels.
A calibration curve plots the instrument's response against standards of known concentration. The concentration of a patient sample is then read from its response on the curve. The curve is valid only within its linear range: samples above it must be diluted and retested, and calibration is repeated as required, for example after a reagent lot change or when quality control fails.