Dengue Literature Review

Tan1997 - ANA Range in Healthy Individuals

4 min read

Tan1997 - ANA Range in Healthy Individuals

Full citation: Tan EM, Feltkamp TEW, Smolen JS, et al. Range of antinuclear antibodies in “healthy” individuals. Arthritis & Rheumatism 40(9), 1997: 1601–1611.

Raw file: [[raw/tan1997.pdf]]

Summary

This landmark multicenter study, conducted under the WHO/IUIS/AF/CDC ANA Standardization Committee, established the reference range of ANA in healthy individuals and compared it with ANA profiles in five rheumatic disease groups. Fifteen international laboratories (6 US, 5 European, 2 Australian, 1 Japanese, 1 Canadian), all experienced ANA reference centres, tested coded sera from 125 healthy adults and patients with SLE, SSc, Sjögren’s syndrome (SS), rheumatoid arthritis (RA), and soft tissue rheumatism (STR) at four dilutions (1:40, 1:80, 1:160, 1:320) on HEp-2 cells. Each lab used its own in-house methodology, making results representative of real-world practice variation.

Key conclusion: a substantial proportion of healthy adults are ANA positive, especially at low dilutions. A cutoff of 1:160 provides the best balance of sensitivity and specificity for discriminating normals from SLE/SSc/SS, but no cutoff can cleanly separate normals from RA or STR patients. The study recommends laboratories report ANA at both 1:40 and 1:160 and provide local normal-population positivity rates.

Study Design

  • Type: Multicenter cross-sectional reference study
  • Sample size: 125 healthy individuals (30 per age group: 21–30, 31–40, 41–50, 51–60 years); disease groups: SLE n=41, SSc n=37, SS n=40, RA n=40, STR n=27
  • Setting: 15 international ANA reference laboratories; coded serum exchange
  • Population: Healthy working adults aged 21–60 years (no physical/mental disabilities); women:men 1.9:1.0

Key Findings

  • ANA positive rates in healthy individuals: 31.7% at 1:40, 13.3% at 1:80, 5.0% at 1:160, 3.3% at 1:320
  • No significant difference in ANA prevalence across age subgroups 21–30, 31–40, 41–50, 51–60 years (χ² = 10.67, p = 0.56)
  • At 1:160 cutoff: sensitivity 95% for SLE, 87% for SSc, 74% for SS; specificity 95% in normals
  • At 1:40 cutoff: specificity only 68.3% (too low to be useful as a cutoff)
  • SLE, SSc, and SS patients could be distinguished from normals; RA and STR could not (ROC areas ~0.50 for RA and STR)
  • Inter-laboratory variability (~50% CV at 1:40) was ~3× intra-laboratory variability; both declined at higher dilutions
  • Low-titer ANA in healthy individuals may reflect: cross-reactive antibodies, transient post-infectious responses, antibodies to low-concentration antigens, or early/subclinical autoimmunity
  • 13% of normal sera came from laboratory personnel working with autoimmune sera; 50% from hospital/university staff; 37% from blood bank donors — unlikely source of significant bias

Methods Used

Entities Mentioned

(None specific to dengue)

Concepts Addressed

Relevance & Notes

This is the foundational reference for interpreting ANA positivity rates in any study population. In the dengue context, Garcia2009 - Long-term Clinical Symptoms Post-Dengue found ANA positivity in 23.1% of post-dengue symptomatic patients — notably higher than the 5.0% healthy-population rate at 1:160 (the dilution most analogous to the IIF method used in the Garcia study), supporting the suggestion of elevated autoimmunity post-dengue. However, the Garcia study used a different IIF dilution context and did not test asymptomatic controls, so direct comparison requires caution.

Limitations: population excludes children (<21 years) and seniors (>60 years); does not include ethnic diversity data; inter-laboratory variability is substantial.

Questions Raised

  • How does ANA prevalence in the healthy population vary above age 60, and how should age-adjusted normals be defined?
  • Does the 1:160 threshold remain appropriate as HEp-2 cell substrates become more sensitive (manufacturers optimizing for proliferation-phase cells)?
  • What is the prognostic significance of low-titer ANA in the general population over time?

Graph View

Backlinks