Primaquine, G6PD Deficiency, and Haemolytic Risk in a Cambodian Farmer
A 32-year-old male farmer from Prey Veng province presents to a referral hospital with a five-day history of dark urine, jaundice, and profound fatigue. Two weeks earlier he was diagnosed with Plasmodium vivax malaria and started on chloroquine plus primaquine 0.25 mg/kg/day for 14 days. He weighs 55 kg. He reports completing five doses. On examination he is pale and tachycardic. Laboratory results: haemoglobin 7.8 g/dL (baseline 13.5), reticulocytes 6%, total bilirubin 3.2 mg/dL with indirect fraction 2.8 mg/dL, lactate dehydrogenase markedly elevated, and haptoglobin low. Blood smear is negative for malaria parasites. No glucose-6-phosphate dehydrogenase (G6PD) testing was performed before primaquine. His older brother reportedly had a similar illness after malaria treatment. The hospital has no G6PD test available on site, and the nearest reference laboratory is 3 hours away. The clinician must decide on immediate management, whether to restart primaquine, and how to counsel the family.
1. Explain the biochemical mechanism by which primaquine can cause haemolysis in a person with G6PD deficiency, and why the brother's history is relevant.
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G6PD is the rate-limiting enzyme of the pentose phosphate pathway. It converts glucose-6-phosphate to 6-phosphoglucono-delta-lactone while reducing NADP+ to NADPH. NADPH is needed to regenerate reduced glutathione, which protects red cells from oxidative damage. Primaquine is an 8-aminoquinoline that is metabolised to reactive intermediates capable of producing hydrogen peroxide and other oxidants. In G6PD deficiency, NADPH supply is inadequate, reduced glutathione falls, and oxidants damage haemoglobin and the red cell membrane. Haemoglobin oxidises to methaemoglobin and precipitates as Heinz bodies; the membrane becomes rigid and fragile, leading to intravascular and extravascular haemolysis. The brother's similar illness suggests an X-linked inherited G6PD variant, because the G6PD gene is on the X chromosome and males are hemizygous. A family history therefore raises the pre-test probability substantially and should be treated as a warning even when no laboratory test is available.
2. Interpret the laboratory results and decide whether primaquine should be restarted. What confirmatory test would you request, and what are the limitations of testing during an acute haemolytic episode?
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The combination of falling haemoglobin, reticulocytosis, indirect hyperbilirubinaemia, high lactate dehydrogenase, and low haptoglobin is a classic haemolytic pattern. The negative blood smear makes relapsing vivax malaria an unlikely explanation for this acute deterioration. Primaquine should be stopped immediately. It should not be restarted until G6PD status is known, because re-exposure can precipitate severe haemolysis. The confirmatory test is a quantitative G6PD enzyme activity assay, ideally with a fluorescent spot test or point-of-care test as a screen. A critical limitation is that during acute haemolysis and reticulocytosis, young red cells have higher G6PD activity, so the result can be falsely normal. Testing should therefore be repeated at least 2–3 months after recovery, when the red cell population is stable. Recent blood transfusion can also confound the result. If radical cure is urgent, the clinician should discuss supervised alternative regimens with a malaria specialist rather than restarting primaquine empirically.
3. Discuss why routine G6PD testing before primaquine is important in Cambodia, and propose a practical approach for a district hospital with no on-site G6PD test.
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Cambodia has both Plasmodium falciparum and P. vivax transmission, and primaquine is used for radical cure of vivax and for gametocytocidal treatment of falciparum malaria. G6PD deficiency is not rare in the region and varies between population groups, so giving primaquine without screening exposes a predictable minority to severe haemolysis. A district hospital without on-site testing can adopt a risk-reduction pathway: use a validated point-of-care G6PD test before starting primaquine whenever available; if unavailable, delay radical cure and give chloroquine alone for the blood stage, with counselling to return immediately if dark urine or jaundice develops. For patients who need gametocytocidal treatment, use a single low dose of primaquine only after assessing G6PD status or according to national guidance. The family should be counselled that dark urine, jaundice, and fatigue are danger signs. Where supervised weekly primaquine regimens are recommended for mild deficiency, they should be given only under direct observation and with clear referral criteria. The key judgement is to avoid unwarranted harm while still treating malaria effectively.