Most laboratories use a two-stage approach for ANA testing, with the first stage being an initial screen at a 1:40 or 1:80 dilution of the patient sample. Negative samples are reported as such and positive samples are titered.
There are two reasons for titering ANA-positive samples. One is to determine the amount of antibody present and the other is to look for multiple patterns. In the case of ANA testing, there is no correlation between titer endpoint and disease activity or severity. However, the higher the titer, the higher the likelihood the patient has one of the SARDs. Often more than one ANA pattern is present in the sample; titering facilitates the identification of these mixed patterns. (Identification of mixed patterns will be covered later.)
The titering scheme most frequently used in ANA testing is two-fold dilutions starting at the initial screening dilution (e.g., 1:40, 1:80, 1:160). While there is no consensus on how far to titer samples, informal communications with laboratories suggest most stop titering at about the 1:2560 dilution (plus or minus one dilution). By this dilution, the samples are often negative and/or no longer contain mixed patterns.
For ANA positive results, the sample is reported as: "ANA positive," followed by the pattern that is indicated along with the titer endpoint. For example: "Sample 12345: ANA positive, speckled, titer: 1:640."
If more than one pattern is present, all patterns are reported along with their respective endpoints. Additionally, many labs will suggest appropriate follow-up testing to identify the antibody(ies) present in the sample. By identifying the specific antibodies present in the sample, the clinician may gain further insight into which of the SARDs the patient has and what other symptoms the patient may develop.
