Adapted blood test predicts risk for anemia following malaria treatment

An existing diagnostic blood test may accurately predict the risk for anemia in patients treated for malaria, according to a report published in Science Translational Medicine.

Artesunate — recommended first-line treatment for severe Plasmodium falciparum malaria — clears the parasite from infected patients better than the previously recommended drug quinine.

However, the agent can induce anemia, called post-artesunate delayed hemolysis.

Because this condition can lead to severe kidney failure, WHO has called for the urgent setup and validation of a simple test that can predict post-artesunate delayed hemolysis in patients with malaria who have been cleared of their infection after treatment with artesunate.

“Post-artesunate delayed hemolysis is linked to the destruction of circulating red blood cells that were once infected but from which parasites have been removed by ‘pitting’ in the spleen after artesunate treatment,” Papa Alioune Ndour, PhD, from the Institut National de la Transfusion Sanguine at Université Paris Descartes in Paris, and colleagues wrote. “In travelers treated with artesunate, post-artesunate delayed hemolysis correlates with the peak concentration of these once-infected red blood cells measured with flow cytometry based on the ring erythrocyte surface antigen, a method potentially available only in well-equipped hospitals.”

The researchers sought to validate a predictive blood test for post-artesunate delayed hemolysis using the parasite protein histidine-rich protein 2 (HRP2), which persists in the blood of artesunate-treated patients with malaria.

Ndour and colleagues used diluted blood samples from 95 Bangladeshi patients and 53 French travelers who became infected with malaria in Africa — all of whom received artesunate — compared with 49 French travelers treated with quinine.

HRP2 persisted in whole blood of artesunate-treated patients with malaria from both Bangladesh (median concentration, 2,693 ng/ml at day 3 vs. 6,139 ng/ml at day 0) and France (median concentration, 8,460 ng/ml at day 3 vs. 10,575 ng/ml at day 0) at higher levels than among quinine-treated patients (median concentration, 2,892 ng/ml at day 3 vs. 15,725 ng/ml at day 0).

Using an optimized membrane permeabilization method, researchers found HRP2 persisted in once-infected red blood cells from artesunate-treated patients by immunofluorescence, Western blotting and electron microscopy. Further, HRP2 was deposited at the membrane of once-infected red blood cells in a pattern similar to that for ring erythrocyte surface antigen, a parasite invasion marker.

Based on these findings, researchers developed a semi-quantitative titration method using a widely available HRP2-based rapid diagnostic dipstick test — the BinaxNOW malaria kit (Alere).

In terms of accuracy for predicting post-artesunate delayed hemolysis, a day 3 titer of 1:500 dilution of whole blood from artesunate-treated patients with malaria predicted subsequent post-artesunate delayed hemolysis with an 89% sensitivity and 73% specificity. At day 7, the sensitivity decreased to 64% and specificity increased to to 80%.

The researchers noted the addition of this test to 28-day follow-up in all patients treated with artesunate could offer two potential advantages for patient management.

“First, there can be greater focus on the subset of patients who are at high risk [for] developing post-artesunate delayed hemolysis, with closer follow-up of clinical, hematological and renal measures, enabling an optimized preparation for blood transfusion,” Ndour and colleagues wrote.

“Second, the approach should allow earlier identification of distinct causes of clinical deterioration in the follow-up period that might be confused with post-artesunate delayed hemolysis,” they added. “Predicting post-artesunate delayed hemolysis with a currently available cheap, simple rapid diagnostic test using a dipstick should ensure a sustained positive outcome in patients with severe malaria treated with artesunate.” – by Kristie L. Kahl

Disclosure: Ndour received grants from Fast-Track North Potomac and Guillin Pharmaceutical. Please see the full study for a list of all other researchers’ relevant financial disclosures.