Results on GeneXpert can be obtained in a day which isn’t the case with TaqMan Assay machine
In what is dual use of one machine, the contraption for testing drug-resistant Tuberculosis (TB) is finding successful use in testing viral load for HIV patients, Indian researchers have discovered.
Doctors at Kasturba Medical College (KMC) in Mangalore decided to put their GeneXpert machine, which is in routine used to detect if the sputum sample is resistant to first line TB drug, Rifampacin, to use for detecting viral loads in HIV patients.
Viral load indicates the number of virus copies in the HIV patient, which gives an understanding of how sick the patient is. Viral load is routinely tested by molecular TaqMan Assay machine and results take up to 7-10 days to arrive. On the contrary, testing on GeneXpert can be achieved in one day.
About 246 HIV positive patients from KMC were recruited in the study between July and September last year. Of these, 196 patients were zeroed in for final analysis as their blood plasma samples had shown accurate results. “The rest were excluded because of insufficient collection of blood, or breaking of cold chain while transporting the samples,” Dr Shrikala Baliga, Professor, Microbiology at KMC told DNA.
Two sets of blood plasma samples were collected for every patient. While one set was tested on GeneXpert machine at the KMC campus and another was sent to an accredited private diagnostic lab in Mumbai for TaqMan Assay test.
While lower limit of viral load detection for GeneXpert is 40copies/ml , for TaqMan Assay it is 38 copies/ml. “Both tests are sensitive to pick up viral load,” said Dr Baliga.
World Health Organisation defines suspected treatment failure in HIV when persistent viral load is above 1000 copies/ml.
After receiving results from both GeneXpert and TaqMan Assay tests, viral load tests for each patient were compared. In various patients, the amount of viral load detected varied from as low as 621 copies/ml to as high as 32,18,605 copies/ml.
In 96.6 per cent of cases, the viral load figures for a patient on both GeneXpert and TaqMan Assay fell within threshold of statistical acceptability. “It means that both tests yielded the same outcome, and one could be replaced for another,” said Dr Baliga.
India has 650 GeneXpert machines in public sector and close to 100 in private sector. Dr Soumya Swaminathan, head of Indian Council of Medical Research (ICMR) agrees that GeneXpert could also serve the purpose of measuring viral load in HIV patients apart from testing drug-resistance in TB.
The study, Use of GeneXpert Tuberculosis testing for HIV viral load testing in India, was published in The Lancet Global Health Journal on Monday.
Market cost
Cost of GeneXpert test for drug-resistant Tuberculosis — Rs 2,000 to Rs 5,000
Cost of TaqMan Assay test of viral load for HIV —
Rs 6,000 to Rs 12,000
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