The International Consensus on ANA Patterns (ICAP) has taken another significant step in the continuous advancement to promote harmonization and understanding in antinuclear antibodies (ANA) of the HEp-2 IFA. As previously anticipated, in the ongoing update of the ANA pattern classification, two newly identified patterns, AC-30 and AC-31, have been incorporated into the ICAP nomenclature and classification tree. A special code has also been assigned to unclassified patterns (AC-XX). This update, dated February 27, 2025, reflects the latest scientific evidence and improves the accuracy of ANA pattern interpretation in clinical and research laboratories worldwide.

_{^{Adapted from www.anapattern.org and from reference [1].}}

Advancing ANA Pattern Classification

Since its establishment, ICAP has provided a standardized framework for the interpretation and classification of ANA patterns, offering clear guidance to clinical laboratories, researchers, and physicians. The HEp-2 IFA test remains a fundamental tool in the detection of autoantibodies, and the refinement of its classification system is essential to maintain diagnostic accuracy.

The addition of AC-30 and AC-31 follows extensive research and expert consensus discussions at the 7th ICAP Workshop in 2023, which recognized the need for further differentiation within the nuclear fine-speckled pattern category. These new patterns contribute to a more nuanced understanding of ANA reactivity and its clinical implications.

Key Characteristics of AC-30 and AC-31

• AC-30: A newly identified nuclear fine-speckled pattern with stained metaphase plate that differs from the established AC-2 (Dense Fine Speckled) pattern. It presents distinct morphologic and immunologic characteristics necessitating its classification as a separate entity. AC-30 showed minimal association with anti-DFS-70 antibodies, in contrast to the strong presence of such antibodies in AC-2 samples [2].

_{^{(A) Dense fine speckled (AC-2) pattern and (B) dense fine speckled pattern with mitotic plate (AC-30). Adapted from reference [1].}}

• AC-31: A refined subcategory of the nuclear AC-4 (Smooth Fine Speckled) pattern, characterized by a myriad of discrete tiny dots. Research indicates a strong association between AC-31 and anti-SS-A/Ro60 antibodies [3], reinforcing its diagnostic significance in autoimmune diseases such as systemic lupus erythematosus (SLE) and Sjögren’s syndrome.

_{^{(A) Smooth fine speckled (AC-4) and (B) myriad discrete speckled (AC-31). Adapted from reference [1].}}

Implications for Clinical Practice and Laboratory Diagnostics

The integration of AC-30 and AC-31 into the ICAP classification tree provides several benefits for laboratory professionals and clinicians:

• Improved Diagnostic Accuracy: Differentiation of fine-speckled nuclear patterns allows for more precise ANA test interpretations, reducing the risk of misclassification.
• Enhanced Standardization: By refining pattern definitions, ICAP ensures greater consistency in ANA reporting among laboratories worldwide, promoting best practices in autoimmune diagnostics.
• Guidance for Further Testing: The association of AC-31 with anti-SS-A/Ro60 antibodies provides clinicians with a valuable diagnostic marker to guide targeted follow-up testing and patient management.

Next Steps and Ongoing Developments

While AC-30 and AC-31 are now officially part of the ICAP classification system, additional resources are being developed to support their implementation and will be updated gradually on the website:

• Example Images: High-quality HEp-2 IFA images will be added to the ICAP website to aid in pattern recognition and differentiation.
• Updated Descriptions: Comprehensive documentation, including immunological and clinical correlations, will be published to provide laboratories with clear interpretative guidance.
• Educational Initiatives: ICAP will continue to engage with the global scientific community through workshops and online resources to ensure widespread adoption and understanding of the new classifications.

The updated ANA pattern classification tree is available, also in different languages, on the ICAP website (www.anapatterns.org).

ICAP remains committed to advancing the standardization of ANA pattern interpretation to ensure that autoantibody diagnostics continue to evolve in line with scientific advances and clinical needs.

[1] Reflecting on a decade of the international consensus on ANA patterns (ICAP): Accomplishments and challenges from the perspective of the 7th ICAP workshop

[2] How consistent are the association of HEp-2 patterns and autoantibody specificities

[3] Strong Association of the Myriad Discrete Speckled Nuclear Pattern With Anti-SS-A/Ro60 Antibodies: Consensus Experience of Four International Expert Centers