Is POC A1c Testing Optimized for Diabetes Screening?

Medscape

28-05-2025

Is point-of-care (POC) glycated hemoglobin (A1c) testing the best choice for diabetes screening?
The option is an attractive one; POC A1c testing provides the convenience of rapid results in a single visit, as well as the potential to reach historically hard-to-reach patient populations, such as those in resource-poor settings. It might also help address the pervasiveness of undiagnosed diabetes, considering almost 1 in 4 US adults are undiagnosed, placing them at risk for serious, long-term, multi-organ complications.
Despite its convenience, accuracy issues have prevented POC A1c testing from replacing whole blood venous laboratory assays for diabetes screening. The American Diabetes Association has also recommended that POC A1c testing be limited to US Food and Drug Administration (FDA)–approved devices. Of note, only one device (of seven that have received regulatory clearance) has received FDA clearance for diagnosis.
Diabetes monitoring is a different story.
Sue Kirkman, MD
'There are definitely advantages to using POC A1c testing in office settings; we use them to monitor patients' diabetes control,' said Sue Kirkman, MD, adjunct (emeritus) professor of medicine in the Division of Endocrinology and Metabolism at the University of North Carolina at Chapel Hill.
'It's great to have a fingerstick test and have results available quickly and right when you are face-to-face with the patient. They're not as accurate as laboratory assays, but lots of studies have shown no difference in outcomes for monitoring,' she said.
Questionable Accuracy
Accuracy has been a long tail that has followed POC A1c testing as a screening strategy. Although there are several systems that meet National Glycohemoglobin Standardization Program standards, manufacturers have only been required to use one lot, with testing being conducted under ideal (vs real world) conditions.
POC A1c testing accreditation has also been waived since the FDA considered these tests easy to conduct. This means that there is no external oversight or quality control, and proficiency training of staff is waived, leaving room for error.
Heather Ferris, MD, PhD
'We've had some pretty significant issues recently with inaccuracies in POC A1c testing to the point where we've had to completely replace our system,' said Heather Ferris, MD, PhD, endocrinologist and associate professor of medicine at the University of Virginia Health in Charlottesville, Virginia. Ferris explained that she and her team ended up having to compare POC and serum results to try to figure out why they were seeing A1cs that were much higher than they were in reality.
'I think in the best-case scenario, POC testing is probably going to be less accurate than a blood test; as physicians, we sometimes don't think as much about test accuracy as we should,' she said.
There are also practical, patient-level considerations.
Kevin Shah, MD
'The first question is, who do you screen?' said Kevin Shah, MD, chief medical officer of Duke Primary Care South Durham, Durham, North Carolina. 'I wouldn't order this for every single patient who walked through the door, so being mindful of patients at the highest risk is important.'
Additionally, POC A1C testing results have been known to be subject to interference by hemoglobin variants, which are present in roughly 5%-7% of the global population.
'Providers should always be aware of the possibility of Hb [hemoglobin] variants, which are especially common in certain patient populations (eg, Black patients),' said Kirkman. 'Most lab assays in the US do not have interference from common variants, but it isn't true of any of the POC tests.'
Data Is Lacking
A 2017 meta-analysis (61 studies; 13 devices) showed that compared with laboratory testing, the majority (9/13) of the devices tested exhibited negative bias; this was significant for three of the devices. Nine of the 13 devices had poor imprecision (note that imprecision goals for A1c should be a coefficient of variation [CV] < 2% for A1c reported in percentage units [or < 3% in SI units, mmol/mol], with CV > 2% at low A1c levels).
Differences were also noted within the devices themselves, ranging from as much as 1.5% A1c below to 1.5% A1c above the comparator lab method.
Findings from a more recent cluster randomized controlled study comparing POC A1c and venous A1c testing for opportunistic diabetes screening in 852 Chinese at-risk patients underscored its favorability amongst patients (uptake was almost twofold higher than venous blood draws; 76.0% vs 37.5%; odds ratio [OR], 7.06; 95% CI, 2.47-20.18; P < .001).
POC testing was also shown to carry an overall 99% higher odds for detecting diabetes vs venous testing (OR, 1.99; 95% CI, 1.01-3.95; P = .048).
However, Kirkman (who was not involved in the study) pointed to several factors inconsistent with real-life scenarios, eg, monthly, rigorous staff proficiency testing and internal/external quality control.
'It wasn't just a comparison of POC vs venous testing; venous blood was drawn at a separate visit on a different day (which led to 17% loss to follow-up),' she said. 'I wonder if a study comparing venous blood draw at the same visit would have shown this much of an advantage.'
Flipping the Script: Consider POC A1c for Monitoring
Using POC A1c testing for monitoring purposes has transformed workflow, said Shah. 'What we've been able to do is create a really efficient process where, when diabetes patients come in, we have the laboratory data available to the physician at the time they see the patient,' he said.
Despite this advantage, ie, the ability to have a productive, meaningful conversation with a patient about how well their condition is controlled or to make medication adjustments, Ferris pointed out that the process itself is complex.
'It's an investment for a small community practice, buying the machine, the cartridges to run the test, and billing for it properly,' said Ferris. 'It also makes sense to have one or two appointed staff to run the tests and get training to ensure you're getting consistency.'
The bottom line? For now, clinicians considering using POC A1c testing for diabetes screening should be aware of its limitations (eg, inherent bias, potential interference with hemoglobin variants, lower accuracy vs laboratory testing) and weigh them against its multiple advantages (eg, rapid turnaround, opportunities for more patient engagement, and faster treatment decisions).
As the technology improves, the landscape might look very different. For now, however, monitoring appears to be the most accurate pathway.
Kirkman, Ferris, and Shah reported no relevant financial relationships.