Antinuclear antibodies (ANA) arc frequently found in healthy populations. To define the prevalence, pattern, and titer of ANA in different groups of the healthy Mexican population, we studied 304 individuals, classified into 3 groups: 104 blood donors, 100 hospital personnel working at The State General Hospital, which included doctors, laboratory technicians, and nurses; and 100 relatives of patient diagnosed either with systemic lupus erythematosus or rheumatoid arthritis, all of them apparently healthy at the time of study. We determined ANA using immunofluorescence microscopy performed on HEp-2 cells. Fluorescence was detected in 165 serum samples (54.3%). The most frequent pattern was the speckled (50.3%). The most frequent dilution was 1:40 (35.4%), followed by 1:80 (13.4%), 1:160 (3.2%), and 1:320 (1.3%). Regarding the results by study group, we found a trend toward higher ANA levels in group 2 (hospital personnel), compared with group I (blood donors) and group 3 (relatives of patients), a trend also reflected,by the increasing frequency of serum titers of 1:80 and higher (P = 0.074). According to occupation, medical doctors showed a higher incidence of speckled pattern when compared with other occupations (P = 0.022). Medical doctors (n = 75) showed also higher titers of this particular pattern (P = 0.03). In group 3, relatives of patients with systemic lupus erythematosus showed the speckled pattern more frequently than relatives of patients with rheumatoid arthritis, in low titers (P = 0.017). We suggest that ANA tests showing speckled pattern should be at a 1:160 titer or higher to be considered positive; other patterns such as homogeneous, peripheral, or centromeric might be considered positive even at low titers (<= 1:40) although this needs investigation. ANA should generally not be tested without clinical indication. Positive ANA finding in the absence of physical signs and symptoms has limited diagnostic utility and should always be interpreted by a rheumatologist, in the context of clinical symptoms and results of laboratory tests for specific autoantibodies. Populations such as doctors and relatives of patients with autoimmune disease tend to presents increased ANA titers.
