HIV-related point-of-care testing can potentially play a major role in accelerating the pace of progress towards achieving the '90-90-90' targets of the UNAIDS (joint United Nations programme on HIV/AIDS). Increasing access to quality and accurate diagnostics which function in low-resource settings is undoubtedly a critically important step in HIV care.
However, challenges remain regarding the appropriate use of point-of-care testing to ensure accurate patient results. Maintaining a high quality of testing while increasing access is critical for better patient care, said experts at the 9th National Conference of AIDS Society of India (ASICON 2016).
Recap: What are the '90-90-90' UNAIDS targets?
* By 2020, 90% of all people living with HIV (PLHIV) should know their HIV status
* 90% of all those with diagnosed HIV infection should be put on antiretroviral treatment (ART), irrespective of their CD4 cell count
* 90% of all people receiving ART should have their viral load suppressed to less than 1000 copies/ml of RNA.
A tall order indeed. The ever increasing serious phenomenon of drug resistance (which will further escalate as more and more PLHIV are put on ART and at least 5% will need second-line ART) magnifies the problem.
What is point-of-care test?
Point-of-care testing implies that the test is available at or near the person being tested; results are made available to the patient during the same visit, (preferably within a very short time) and then used immediately for patient care and referral. Point-of-care tests for diagnosing HIV, estimating the CD4 cell count, measuring viral load and detecting drug resistance play a major role in achieving our goal of eliminating AIDS.
Any point-of-care test should:
- be simple to use and easy to perform, requiring minimal training;
- be robust with no requirement of any special equipment or refrigeration of reagent;
- give results rapidly, preferably within 30 minutes or so;
- have high sensitivity and specificity; and
- be usable in remote/hard to reach places and in communities.
Point-of-care test for diagnosing HIV
Rapid tests being extensively used for HIV diagnosis for the last 15 years are examples of point-of-care tests and their scale up has increased the access to HIV testing in India and globally.
A point-of-care test using oral fluid for HIV diagnosis is very user-friendly, as giving oral samples is less invasive for the patient and sample collection has less biosafety hazards for the collector of sample. Moreover turnaround time with oral sample is just 45 minutes as compared to 3 hours with blood samples.
Dr Madhuri Thakar of NARI (National AIDS Research Institute) - part of Indian Council of Medical Research (ICMR), shared with CNS (Citizen News Service) that NARI evaluated 3 such different types of kits for the detection of antibodies of HIV1/ HIV2 in human oral fluid based on the principle of immune chromatography.
They found that:
- Calypte Aware for HIV1/2 is 100% sensitive and 99.7% specific
- Oraquick Rapid for HIV1/2 is 100% sensitive and 99.2% specific
- Oracheck for HIV is 98.07% sensitive and 100% specific.
While the advantages of these diagnostic kits are many, Dr Thakar cautioned that, “The positive results need to be confirmed by blood test and in case of negative result, test should be repeated after 3-6 months. The external quality assessment (EQA) participation of the centre doing the blood test is a must”.
The WHO pre-qualified Xpert HIV-1 Qual, which is based on GeneXpert technology, is another qualitative test that provides on-demand molecular testing for early HIV diagnosis. It is a qualitative in vitro diagnostic test and can detect HIV-1 in whole blood and dried blood spots from individuals, including infants within 90 minutes.
Point-of-care test for estimation of CD4 count
CD4 count is a gatekeeper for assessing immune status and establishing eligibility for treatment and care. It is important to increase access to CD4 count at earliest after knowing HIV result to know requirement of ART initiation.
Dr Thakar said that most of the available point-of-care technologies for CD4 count used in India are battery-operated, use thermostable reagents, there is minimal or no sample preparation, and all use finger prick/ venous blood.
The National AIDS Research Institute (NARI) evaluated two such machines: BD FACSPresto, (which is a near point-of-care CD4 counter) and the PIMA CD4 Analyser (Alere).
The WHO pre-qualified and US-FDA approved BD FACSPresto is an image based cell and absorbance measurement technology and measures absolute CD4 cell count, CD4 and total haemoglobin. Results are available in less than 22 minutes and can be read within up to 2 hours. It uses dried reagents, is light weight, portable and battery operated. A multi-site study done in India, Thailand, Kenya, China and USA found the error rate to be less than 5%.
The WHO prequalified PIMA CD4 Analyser (Alere) was the 1st point-of-care CD4 counter that came in the market. It measures only absolute CD4 counts using venous or capillary blood. Study results in India have shown good correlation at all CD4 ranges and 91% requiring ART were correctly identified. Number of invalid tests was less than 7%. But cost is high at $ 6500-12000 per equipment and $ 6-12 per test.
The point-of-care CD4 equipment/ methodologies are still in the process of being implemented in India. Dr Thakar cautioned that point-of-care test is not the answer for every situation. In the case of very high load of patients on a daily basis HIV ELISA or conventional CD4 machines would be more useful.
Point-of-care test for Viral Load
Dr David Katzenstein, Emeritus Professor, Medicine (Infectious Diseases), Stanford School of Medicine, said that while access to ART worldwide has significantly improved but coverage is still very heterogenous. The last '90' of the '90-90-90' cascade (90% suppressed viral load) is critically important. There is a huge demand for viral load testing as less than half of those on ART have their viral load tests.
Monitoring of viral load to identify virologic failure is critical for care of PLHIV. Having point-of-care test for viral load testing has many benefits: convenience, portability, speed, quality assurance and decreased laboratory workload.
Dr Ellen Jo Baron, Emeritus Professor of Pathology at the Stanford University Medical Center and associated with Cepheid, gave the example of Cepheid's Xpert HIV1 Viral Load assay which is strictly not a point-of-care test. But it can be done in a small laboratory that has necessary resources. It is fully automated, can identify all the sub-types and gives results in 90 minutes. Dr Baron shared that Cepheid has got a grant to create a finger-stick test for viral load testing, which is battery operated, portable, rugged, relatively affordable, can be run on omni instrument at remote sites. It is hoped to give results in less than 60 minutes, with an accuracy of 500 copies/ml.
Point mutation assays at near point-of-care or at point-of-care are the hope that in future we will be able to provide information to all PLHIV that is critical to their long term care.
Point-of-care test for finding drug resistance
Dr Rami Kantor, Associate Professor of Medicine, Brown University, USA, elaborated the importance of point mutation assays and drug resistance testing in HIV management. He said that, “Transmitted and acquired resistance is a major problem for patient care in India and globally. Global incorporation of drug resistance testing into clinical care is inevitable. Point mutation assays are more sensitive and so can detect more drug resistance and should continue to be developed." Conventional drug resistance testing, using 'Sanger' sequencing, is the most common assay used globally. But apart from being expensive, labour intensive and time consuming, its sensitivity is also less and so there is likelihood of under estimation of resistance.
More advanced assays to determine drug resistance mutations are emerging to identify lower levels of mutations and also to detect single mutations. Dr Kantor mentioned one such assay - the Oligonucleotide Ligation Assay (OLA). It amplifies the virus and then does ligation to find if the mutation is there or not. It is:
(i) highly sensitive and detects mutant frequency;
(ii) 100% specific;
(iii) quantifies mutant frequencies; and
(iv) requires minimal equipment of a simple thermocycler costing US$ 3000.
However it requires technical skill, turn around time is 8 hours and it is not strictly a point-of-care test.
Important 'cog-in-the-wheel' but not the only one!
Point-of-care test can result in timely initiation of ART and also reduce loss to follow up of patients who drop off through cascade of linkage to care and treatment. Another impact could be to improve patient care and improved public health response. But having point-of-care test alone will not be able to deliver the desired results. Rapid results may not always translate into rapid correct treatment/ follow up in all settings. The right test ordered at the right time; rapid reporting and delivery of results; and the ability to act quickly on the results to improve patient management - all of these are equally important to end the AIDS epidemic.
(Shobha Shukla is the Managing Editor of CNS (Citizen News Service). Follow her on Twitter: @Shobha1Shukla)