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Dried Blood Spot Testing Rivals Conventional Methods for NMOSD Diagnosis
A recent multicenter study showed that dried blood spot testing for neuromyelitis optica spectrum disorder provided high accuracy and practicality in resource-limited settings.
Nisa Vorasoot, MD
(Credit: X)
A new study recently published in Annals of Clinical and Translational Neurology demonstrated the strong diagnostic accuracy and specificity of dried blood spot (DBS) testing, particularly with advanced flow cytometry techniques, in detecting aquaporin-4-IgG (AQP4-IgG) for neuromyelitis optica spectrum disorder (NMOSD) compared with conventional serum testing.1 These results suggest that DBS testing could potentially transform how the disease is diagnosed by offering a reliable, cost-effective alternative to gold standard testing.2
The study analyzed data from 150 participants, including 47 NMOSD cases and 103 controls, comparing DBS with serum testing. Findings revealed that DBS testing achieved an area under the curve (AUC) of 0.97 (95% CI, 0.92–0.99) for accuracy. Notably, sensitivity was 87.0% (95% CI: 0.74–0.95) and specificity reached 100% (95% CI, 0.96–1.00) when flow cytometric live-cell-based assays (CBA) were used. Results revealed that overall, this performance was comparable to serum testing, showing a strong correlation between DBS and serum samples (Spearman's correlation coefficient, 0.82).
“Our study established the reliability and diagnostic potential of DBS for detecting AQP4-IgG. The findings demonstrated that AQP4-IgG detection using DBS exhibits both high sensitivity and high specificity, almost comparable to the current gold standard serum testing,” lead author Nisa Vorasoot, MD, research fellow in autoimmune neurology at Mayo Clinic, and colleagues wrote.1 “This method proved feasibility in resource-limited regions and within the United States, performed by patients themselves. Moreover, our approach indicates the potential for expanding the use of DBS to test for other neurological antibodies or neuroinflammatory biomarkers.”
In this prospective study, conducted between April 2018 and October 2023, researchers collected blood samples from patients with NMOSD and controls at medical centers from 3 countries including the United States, Uganda, and Guinea. Investigators processed the gathered samples utilizing filter paper cards for DBS and then compared them against concurrent serum samples. Both types of samples were evaluated for AQP4-IgG serostatus using flow cytometry and enzyme-linked immunosorbent assay (ELISA) techniques. Overall, the study aimed to assess how closely DBS results aligned with serum-based gold standard testing.
Although findings showed that flow cytometry proved highly effective for DBS testing, authors noted that ELISA revealed mixed results. Investigators reported that DBS-ELISA exhibited lower sensitivity at 65.2% (95% CI, 0.43–0.84) compared with serum-ELISA at 69.6% (95% CI: 0.47–0.87), though findings demonstrated that DBS maintained high specificity at 95.2% (95% CI, 0.76–0.99). Moreover, DBS samples retained their diagnostic reliability for up to 24 months, which researchers noted highlights their potential for long-term storage and transportation in diverse environments.
All told, the study had several limitations including the absence of serological data from patients in the Republic of Guinea because of logistical challenges with antibody testing and serum transport. Researchers also noted that variations in blood spot sizes on DBS filter papers may have resulted in inconsistent sample volumes, which could have affected sensitivity and contributed to false-negative results. In addition, discrepancies in collection dates between some serum and DBS samples could have influenced test outcomes. Therefore, investigators suggest that further research is needed with larger sample sizes, diverse clinical settings, and a focus on testing serum transport at room temperature to address these limitations and enhance the method’s applicability in resource-limited regions.
“The versatility and practical advantages of DBS have positioned it as a valuable tool in diagnostic testing, especially in situations where traditional blood sample collection methods encounter logistical challenges,” Vorasoot et al noted.1 “Our study obtained samples from Uganda and the Republic of Guinea, where antibody testing is unavailable, demonstrating the feasibility of accessing antibody testing from a high-income country through DBS collection in resource-limited settings. Moreover, DBS can serve as a viable transfer method for ELISA, offering potential cost savings on shipping, and expediting turnaround times when performed locally.”
