Background/Purpose:
National Jewish Health (NJH) is a tertiary referral center for pulmonary and
immunologic disease.  The infectious disease division at NJH specializes in the
care of patients with chronic pulmonary infections, especially those with nontuberculous
mycobacterial disease (NTM). The NTM patients have bronchiectasis and their
sera are sent for autoantibodies to determine if there may be an underlying
concomitant rheumatic disease predisposing to infection.  It is well known that
chronic infectious disease may increase the false positive rate of some
immunologic tests.  An example is a rheumatoid factor found in tuberculosis
and/or hepatitis C.  We chose to retrospectively analyze patients with NTM and
autoantibodies to determine if these laboratory tests were more frequently
positive in the absence of defined rheumatologic illness.

Methods:  We
queried our electronic medical record from February 2008 through May of 2015. 
We defined NTM cases as those with positive cultures at our institution or an
appropriate ICD-9 code within the medical record.   Patients with defined
autoimmune disease (ICD- 9 codes with 710 or 714) and tuberculosis were
excluded from our entire analysis.  Antinuclear antibody (ANA), rheumatoid
factor (RF), cyclic citrullinated peptide (CCP), SSA and SSB results were
tabulated.  We used a Chi-squared analysis to determine if these autoantibodies
were more likely to return as positive in the NTM patients when compared with
our overall patient population. 

Results: During
the study period, 3,721 cases of NTM were seen at NJH and 65% had at least one
autoantibody resulted. RF, CCP and ANA testing were not more likely to return
as positive in the setting of NTM. Furthermore, non-NTM cases within NJH were
more likely to have a positive SSA or SSB antibody (OR 0.53, χ²
19.1 with 1DF, p 0.0001 or OR 0.41, χ² 10.0 with IDF, p 0.0015
see Table 1).

Conclusion:  Patients
with NTM were not more likely to have a positive ANA, RF, CCP as compared to
the overall population. Additionally, the SSA and SSB were less likely to be
positive in patients with NTM. This may indicate that NTM does not cause false
positive results as is seen in diseases like tuberculosis.  Therefore, in this
setting, positive autoantibodies could indicate the presence of occult
autoimmune disease. 

Figure 1: 2 x 2 contingency tables representing
individual patients and autoantibody results (excluding patients with defined
autoimmune disease), odds ratios (OR), Chi-squared test ( χ²),
and p values