Blood Test Helps PCPs Dx AD With Specialist-Level Accuracy

LONDON — Blood-based biomarker (BBM) testing may enable primary care physicians (PCPs) to diagnose Alzheimer’s disease (AD) as accurately as dementia specialists, potentially expanding access to accurate diagnosis beyond memory clinics, new research suggests. In a prospective study of more than 1300 patients, PCPs achieved 93% diagnostic accuracy after reviewing BBM results, which was comparable to the 94% accuracy of dementia specialists. The test also changed clinicians’ diagnoses and management plans in a substantial proportion of cases.

Sebastian Palmqvist, MD, PhD

“By equipping primary care practitioners with blood test results, we see that they’re as accurate as dementia experts in definitely ruling out [AD],” study investigator Sebastian Palmqvist, MD, PhD, senior consultant neurologist and associate professor, Lund University, Lund, Sweden, told Medscape Medical News . Using BBM results also had “a clear effect” on how clinicians managed patients, Palmqvist said. After reviewing the test results, they changed their planned management strategy for more than 60% of patients. The findings were presented on July 14 at Alzheimer’s Association International Conference (AAIC) 2026 .

Testing Clinical Utility

BBMs accurately identify the hallmark AD pathologies, amyloid-beta and phosphorylated tau (p-tau), but until now it has been unclear whether they meaningfully influence clinicians’ diagnostic and management decisions. Although BBMs have proved highly accurate for detecting AD pathology, whether they improve everyday clinical decision-making has remained an open question. A study presented at AAIC 2024 and later published in JAMA demonstrated that BBMs of amyloid-beta and p-tau accurately identified AD in patients with cognitive symptoms in both primary and specialty care. The current study builds on those findings by examining how access to BBM results changes clinicians’ diagnoses and management decisions. Rather than evaluating the accuracy of the blood test itself, the researchers examined how access to the results influenced physicians’ diagnoses and clinical management. It included a primary care sample of 443 participants — 257 with mild cognitive impairment (MCI) and 186 with dementia (mean age, 77.8 years; 47.9% female). Researchers analyzed plasma using the PrecivityAD2 test, which measures amyloid-beta and p-tau217, with results reported as negative, likely positive, or positive — with upper and lower thresholds to help rule AD in (positive predictive value [PPV]) or out (negative predictive value [NPV]). A total of 165 physicians completed questionnaires before and after receiving the BBM test results, including 156 general practitioners from 25 primary care clinics. Some questions focused on diagnosis, for example, asking physicians to identify the most likely cause of a patient’s cognitive impairment, whereas others addressed clinical management, such as whether they planned to refer the patient to specialty care, order additional testing, or initiate AD treatment.

PCPs vs Dementia Specialists

The head-to-head comparison involved the same primary care patients being evaluated independently by both PCPs and dementia specialists, including neurologists, geriatricians, and psychiatrists — before and after disclosure of the BBM results. “We wanted to understand how a dementia expert interprets or uses the blood test result differently from the [PCP],” said Palmqvist. Diagnostic accuracy was determined by comparing physicians’ assessments with a reference standard consisting of a consensus clinical diagnosis by dementia experts and confirmation with cerebrospinal fluid amyloid-beta 42/40 testing or amyloid PET, with adjudicators blinded to the BBM results. Overall, 42.2% of patients had a negative BBM result, 18.5% had a likely positive result, and 39.3% had a positive result. Negative results were more common among patients with MCI than among those with dementia (50.6% vs 30.6%), whereas positive results were more common among those with dementia than among those with MCI (50.5% vs 31.1%). BBM results prompted PCPs to revise their diagnosis in 30.0% of patients and dementia specialists in 27.1%, a difference that was not statistically significant ( P = .34). Before reviewing the BBM results, dementia specialists were better than PCPs at ruling AD in and out. After reviewing the results, however, PCPs matched specialists in ruling out AD, with similar NPVs (89% vs 87%). Specialists retained an advantage in ruling in AD, with a PPV of 96% vs 89% for PCPs. “This was significant, meaning that experts were significantly better at ruling in [AD] but not ruling it out,” said Palmqvist.

Management Change

After reviewing the BBM results, diagnostic accuracy increased from 62% to 88% among PCPs and from 73% to 93% among dementia specialists, narrowing the gap between the two groups to just 5 percentage points. “PCPs were actually just as good as the dementia experts at ruling out [AD] when equipped with the blood test results,” said Palmqvist. “After seeing the blood test results, the differences were very, very small.” BBM results also had a substantial impact on clinical management. PCPs changed their planned management strategy in 62.8% of patients after reviewing the test results, with changes affecting referrals, additional testing, and treatment decisions. One of the biggest changes involved referrals. Negative blood test results led PCPs to substantially reduce referrals for specialty evaluation, potentially sparing patients unnecessary investigations and reducing healthcare costs, Palmqvist said. In contrast, referrals increased after a likely positive result, which generally requires confirmation by a dementia specialist. Positive test results did not increase referrals, reflecting Swedish practice, where PCPs are expected to diagnose many patients with AD because specialty memory clinics lack the capacity to evaluate everyone. Palmqvist noted that referral patterns may differ in healthcare systems, where all patients with suspected AD are referred to specialists. Overall, both PCPs and dementia specialists rated the blood test as highly useful, assigning it a median score of 9 out of 10. PCPs found likely positive results somewhat less helpful (median, 7/10) than clearly negative or positive results.

‘Hopeful News’ for Patients

In a statement, Sheena Aurora, MD, vice president of medical affairs at Alzheimer’s Association, called the findings “hopeful news” for patients, many of whom face long waits for an accurate diagnosis and treatment. The results suggest BBMs can improve diagnosis and medical management in both primary and specialty care, demonstrating “great clinical utility,” she said. Stephen Salloway, MD, professor of psychiatry, human behavior, and neurology at Brown University in Providence, Rhode Island, who was not involved in the research, said the findings build on the group’s 2024 JAMA study and further support the role of BBMs in improving AD diagnosis across care settings. “Reliable blood tests should have a major impact on the diagnosis and treatment of AD in primary care and specialty settings,” Salloway said. He cautioned, however, that additional studies in more diverse populations are needed and that broader clinical adoption will depend on reimbursement from Medicare and other insurers. Maria C. Carrillo, PhD, chief science officer and medical affairs lead at Alzheimer’s Association, said she was particularly encouraged by the improvement in PCPs’ diagnostic accuracy after they reviewed the BBM results. As demand for testing grows, she noted, Alzheimer’s Association has developed a clinical decision tree to help PCPs determine which patients are appropriate candidates for BBM testing. The investigators reported no relevant disclosures. Aurora, Salloway, and Carrillo reported no disclosures.