Rods & Rings (AC-23) Pattern: Navigating Challenges

The AC-23 pattern, also known as the “rods and rings” pattern, is a cytoplasmic fluorescence pattern recognized by the International Consensus on ANA Patterns (ICAP). On HEp-2 cells, it is characterized by short, rod-shaped and ring-shaped filamentous structures distributed throughout the cytoplasm, occasionally in the perinuclear region. As this pattern is detected through indirect immunofluorescence microscopy only, its recognition relies on careful visual examination by a trained observer, with attention extending beyond the nucleus. Consequently, automated screening systems and solid-phase assays may fail to identify this pattern.

Clinically, the AC-23 pattern is most strongly associated with chronic hepatitis C virus (HCV) infection in patients treated with pegylated interferon-alpha and ribavirin. Ribavirin inhibits inosine monophosphate dehydrogenase (IMPDH), a mechanism thought to contribute to the induction of the associated autoantibody response. However, AC-23 has also been reported in individuals without HCV infection, including patients with autoimmune disorders such as systemic lupus erythematosus, Sjögren syndrome, and primary biliary cholangitis, as well as in apparently healthy individuals. Evidence regarding its associations with specific treatment regimens, hepatic fibrosis, and cerebrovascular risk remains limited and inconsistent. Therefore, the AC-23 pattern should not be considered diagnostic of a particular disease but rather a laboratory finding that requires interpretation in the context of the patient’s clinical presentation and treatment history.

In routine laboratory practice, the AC-23 (rods and rings) pattern may be overlooked, resulting in the sample being reported as “ANA negative.” Explicitly identifying and reporting this pattern helps prevent misclassification, alerts clinicians to the possibility of previous or ongoing HCV treatment and contributes to local data on its prevalence and clinical distribution. Furthermore, its recognition reflects adherence to ICAP nomenclature and a comprehensive assessment of the entire cell rather than focusing solely on nuclear fluorescence. In conclusion, careful examination, accurate identification and reporting of the rods and rings pattern are essential for reliable laboratory interpretation and appropriate clinical correlation.