We summed the characteristics of each IF category, and noticed that both cohorts revealed 7.4 % and 6 %, respectively of sera, which did not show positive IF at an acceptable dilution (only by 1:10) or were fully negative in IF test, but were clearly positive in immunoblot test. This was especially alarming with anti-Scl-70 antibodies, which could be barely recognized in IF test, but were clearly present in 53 of 407 positive stained strips (cohort A) and/ or 14 out of 156 positive stained strips (cohort B).