Paper I — 2023 January (Supplementary) (2019 Scheme) — Q3
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Paper I
2023 January (Supplementary) (2019 Scheme) · 100 marks · 180 min
Question
Quantitative buffy coat examination– principle, applications, advantages and
Disadvantages. (3+1+2+2)
Q38 marksShort Essays
Answer
Quantitative Buffy Coat (QBC) examination
Principle: a blood sample is collected into a specially designed capillary tube pre-coated with acridine orange (a fluorescent DNA/RNA-binding stain) and an anticoagulant; after centrifugation, blood components separate by density, with parasites/leukocytes concentrating at the buffy coat layer (between plasma and packed RBCs); a floating plastic float within the tube expands this thin buffy coat layer, and the tube is examined under a fluorescence microscope, where parasitized cells/organisms fluoresce brightly (their nucleic acid taking up the acridine orange stain) against the surrounding tissue, allowing rapid detection even at low parasite density.
Applications: primarily used for rapid detection of blood parasites, most notably Plasmodium species (malaria) — also used for detecting microfilariae, trypanosomes, and can assist in leukocyte/platelet quantification given the buffy coat separation principle.
Advantages:
Higher sensitivity than conventional thick smear for detecting low-density parasitaemia, since the technique concentrates the parasites into a thin, easily-scanned layer.
Faster to perform and screen than a conventional Giemsa-stained smear.
Technically less demanding for the initial screening step.
Disadvantages:
Cannot reliably distinguish Plasmodium species (unlike a conventional Giemsa-stained thin smear, which allows detailed species-level morphological identification) — a significant limitation, since species identification (particularly confirming/excluding P. falciparum) is clinically important for treatment decisions.
Cannot accurately quantify parasitaemia (percentage of infected RBCs) with the same precision as smear microscopy — important for assessing disease severity in falciparum malaria.
Requires a fluorescence microscope, which is more expensive and less widely available than a standard light microscope.
More expensive per test (specialized capillary tubes) than conventional smear examination.
A confirmatory Giemsa-stained smear is generally still required for definitive species identification once QBC screening is positive.
