How is point-of-care testing growing?
A: The COVID-19 pandemic has been a strong force in decentralizing diagnostics, from a lab personnel shortage to an increase in over the counter (OTC) home testing. Infectious disease testing, once the realm of central labs, is growing, led by SARS-CoV-2 antigen tests. Most of the latter tests use nasal swabs and detect nucleocapsid proteins of the virus. As long as they are used according to instructions, POC tests deliver quick and early results to both patients and clinicians alike.
There are now point-of-care (POC) tests for many diseases that are inexpensive, easy to use, robust, and widely used. Many POC tests use lateral flow immunoassay technology, where the built-in control works automatically. For professionals, POC tests are especially useful for emergency room staff and for first responses, for example, to diagnose traumatic brain injury.
Infectious disease testing is about 37% of the POC market. Flu testing is the largest contributor, and about 80% of flu testing in the U.S. is performed in the physician office setting. Testing for syphilis and gonorrhea by POC devices also has been a success story (1).
Another POC growth areas is testing for drugs of abuse in urine or other body fluids that use immunoassay screening cups. They are also easy to use and include controls. In one POC kit, the assay components are incorporated in the caps of the cup. The user ensures a minimum volume of urine in the cup and tilts it to activate test, with qualitative results in 5 minutes. Depending on the drug to be tested, and cut-offs used, these POC tests may have greater than 90% concordance with the gold standard chromatography/mass spectrometry assays.
Urine dipstick technology also is now available for albumin/creatinine ratio, a marker of kidney health. Serum creatinine and cystatin C, both kidney markers, also have POC tests.
Can home testing keep expanding?
The rapid proliferation and public focus on at-home testing for SARS-CoV-2 is unique. But history shows such expansion has been building for years. Home testing certainly is not new: patients have used blood glucose meters since 1981. And since 2019, hemoglobin A1c has joined the glucose testing in POC diabetes market. Similarly, while home pregnancy tests have been on market since 1976, the fast and easy to use tests the public is used to came to market only in the 1980s.
POC tests for coagulation also have become essential. These make self-monitoring of anticoagulants, such as warfarin, easier.
Of course, another exciting opportunity of at-home POC is molecular testing, even beyond SARS-CoV-2. POC has become established for fecal occult blood testing to screen for colorectal cancer. It is hoped that incorporating immunoassays and molecular testing in stool tests will increase early detection of colorectal cancer.
What are current challenges for POC testing?
One challenge of POC testing is quality control and result reporting. Laboratories can deal with these by employing wireless laboratory information system connectivity for POC devices (2). A second challenge is test errors; home tests should be made robust, with results as good as central labs. But even central lab tests occasionally suffer from various kinds of interference. Analytical interference is observed in POC as well. The solution here is similar to that of the central lab: If a result does not match the clinical picture—or other test results—serial dilution of the sample can confirm suspected interference and deviation from linearity (3). Most assay reagents now contain various blockers, for example, heterophilic antibody blockers, to reduce such interference.
Pradip Datta, PhD, DABCC, is a senior staff scientist with Siemens Healthcare Diagnostics in Newark, Delaware. Email: [email protected]
References
- Adamson P, Loeffelholz, M, Klausner J. Point-of-Care Testing for Sexually Transmitted Infections: A Review of Recent Developments. Arch Pathol Lab Med Vol.144, 1344-1351. doi: 10.5858/arpa.2020-0118-RA
2. Plebani M. Does POCT reduce the risk of error in laboratory testing? Clin Chim Acta. 2009; 404: 59-64.
3. Datta P. How to detect and solve immunoassay interference. Clin Lab News, October 2015.