Range of antinuclear antibodies in “healthy” individuals compared with that in patients with Lupus, Scleroderma, RA

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OBJECTIVE: To determine the range of antinuclear antibodies

(ANA) in “healthy” individuals compared with that in patients

with systemic lupus erythematosus (SLE), systemic sclerosis

(SSc; scleroderma), Sjogren’s syndrome (SS), rheumatoid

arthritis (RA), or soft tissue rheumatism (STR).

METHODS:

Fifteen international laboratories experienced in performing

tests for ANA by indirect immunofluorescence participated in

analyzing coded sera from healthy individuals and from

patients in the 5 different disease groups described above.

Except for the stipulation that HEp-2 cells should be used as

substrate, each laboratory used its own in-house methodology

so that the data might be expected to reflect the output of a

cross-section of worldwide ANA reference laboratories. The

sera were analyzed at 4 dilutions: 1:40, 1:80, 1:160, and

1:320.

RESULTS: In healthy individuals, the frequency of ANA

did not differ significantly across the 4 age subgroups

spanning 20-60 years of age. This putatively normal population

was ANA positive in 31.7% of individuals at 1:40 serum

dilution, 13.3% at 1:80, 5.0% at 1:160, and 3.3% at 1:320. In

comparison with the findings among the disease groups, a low

cutoff point at 1:40 serum dilution (high sensitivity, low

specificity) could have diagnostic value, since it would

classify virtually all patients with SLE, SSc, or SS as ANA

positive. Conversely, a high positive cutoff at 1:160 serum

dilution (high specificity, low sensitivity) would be useful

to confirm the presence of disease in only a portion of cases,

but would be likely to exclude 95% of normal individuals.

CONCLUSION: It is recommended that laboratories performing

immunofluorescent ANA tests should report results at both the

1:40 and 1:160 dilutions, and should supply information on the

percentage of normal individuals who are positive at these

dilutions. A low-titer ANA is not necessarily insignificant

and might depend on at least 4 specific factors. ANA assays

can be a useful discriminant in recognizing certain disease

conditions, but can create misunderstanding when the

limitations are not fully appreciated.

Tan EM, Feltkamp TE, Smolen JS, Butcher B, Dawkins R, Fritzler MJ, Gordon T, Hardin JA, Kalden JR, Lahita RG, Maini RN, McDougal JS, Rothfield NF, Smeenk RJ, Takasaki Y, Wiik A, Wilson MR, Koziol JA

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