Chapter 2 · Autoimmune serology

Autoimmune tests such as ANA, ANCA, anti-dsDNA, rheumatoid factor, anti-CCP, and antiphospholipid antibodies must have documented reference intervals and clinical interpretation guidance. ANA screening by IIF requires trained observers and documented pattern reporting (homogeneous, speckled, centromere, nucleolar). Positive ANA screens must trigger reflex testing for specific antibodies (ENA panel) per the laboratory’s documented protocol.

Chapter 2 · Practical example

ANA IIF — titre, pattern, and reflex testing

An ANA result without a pattern and appropriate reflex testing is clinically incomplete. Pattern reporting guides differential diagnosis and the next investigation step.

▲ The situation

A strongly positive ANA is reported on a patient presenting with arthralgia and fatigue. The result is released as: ANA positive, titre 1:640.

Reference: ISO 15189:2022 Clause 7.5; ACR ANA Reporting Guidelines

✓
Good practice

The scientist reviewing the result adds the pattern — speckled — and initiates reflex ENA testing per the laboratory’s algorithm for ANA titres above 1:160. The full report: ANA positive, titre 1:640, speckled pattern. ENA screen initiated per reflex protocol — see separate report. This gives the rheumatologist immediate direction for differential diagnosis (speckled ANA with positive ENA is associated with conditions such as MCTD, SLE, or Sjogren’s syndrome).

✗
Poor practice

The result is released as ANA positive, titre 1:640. The clinician refers to rheumatology. The rheumatologist requests an ENA screen — a test the laboratory would have added automatically if a reflex protocol had been triggered. The ENA result arrives six weeks later, delaying diagnosis in a patient with early MCTD.

● What this means for your practice

ANA titre and pattern are inseparable in clinical reporting. A positive ANA without a pattern forces the clinician to return for more information. Establish reflex ENA testing for all ANA titres above 1:160 — document it, train all scientists, and build it into the result authorisation process.