Alzheimer’s Blood Tests Help Primary Care Doctors Make Better Diagnoses

Blood test results helped primary care physicians diagnose Alzheimer’s disease with nearly the same accuracy as specialists, a study of Swedish patients with cognitive impairment showed.

Primary care physicians changed their diagnosis in 30% of patients after they reviewed blood test results, reported Sebastian Palmqvist, MD, PhD, of Lund University in Sweden.

Diagnostic accuracy rose from 62% to 88%, giving primary care physicians similar negative predictive values as dementia experts for ruling out Alzheimer’s disease, Palmqvist said at the Alzheimer’s Association International Conference.

Test results changed clinical management for 62.8% of patients. This included specialist referrals, additional exams, and starting or stopping medications.

Rapid advances in Alzheimer’s blood tests have fueled extensive research into their ability to identify the disease.

“All previous studies have asked how accurate these blood tests are. We asked a different question, which is what happens once the result actually reaches the physician. That is what matters in the end for the patient,” Palmqvist said.

“A diagnostic test is only worth having if it changes what the doctor does,” he told MedPage Today. “Accuracy on its own does not help anyone.”

In 2025, the FDA cleared two diagnostic blood tests for Alzheimer’s disease: one to help clinicians identify Alzheimer’s in people with signs and symptoms, the other to rule out Alzheimer’s disease in primary care.

Lab-developed tests not approved by the FDA are also on the market. Last year, the Alzheimer’s Association issued guidance outlining strict sensitivity and specificity parameters for Alzheimer’s blood tests to either triage or diagnose people with cognitive impairment.

“Because not all blood-based biomarker tests meet the same standards for accuracy, clear evidence-based guidance is essential,” said Sheena Aurora, MD, of the Alzheimer’s Association. “These tools help clinicians make informed decisions about using the right blood-based biomarker test for the right patient at the right time.”

Palmqvist assessed data from 443 patients with cognitive impairment who underwent a dementia evaluation in primary care from February 2023 to June 2026. Of these, 257 met criteria for mild cognitive impairment and 186 had dementia.

Patients had a mean age of 78 years, and 48% were women. Patients with mild cognitive impairment had a mean Mini-Mental State Examination (MMSE) score of 26.4; those with dementia had a mean MMSE score of 23.1. MMSE scores range from 0 to 30, with lower scores indicating more cognitive impairment.

Blood samples were analyzed prospectively using the PrecivityAD2 algorithm, which uses mass spectrometry to measure two biomarkers — the amyloid-beta 42/40 ratio and the percentage of phosphorylated tau 217 — in plasma. Results were reported as an amyloid probability score that was negative, likely positive, or positive.

A total of 156 primary care physicians completed questionnaires before and after the blood test results were disclosed. The reference standard was a consensus diagnosis that included an expert panel. Change in clinical management was assessed as a composite endpoint of referrals, examinations, and other actions.

The blood test was most useful for ruling out Alzheimer’s, Palmqvist observed. Primary care clinicians remained cautious about using it to diagnose the disease, preferring to send patients to specialists for confirmation.

Primary care clinicians also rated the blood test as very helpful in the diagnostic evaluation, giving it a median helpfulness score of 9/10, he noted.

“To our knowledge, this is the first study to look directly at what a primary care physician does with a blood biomarker result,” Palmqvist said. “Most patients with memory complaints are first assessed in primary care, and that is where diagnostic accuracy is lowest and where the potential gain from a blood test is therefore greatest.”