– No repeat tests within nine months

Repeat ANA/ENA requests: we will no longer do an ANA and/or ENA if one has already been done in the previous nine months

Background:

Antinuclear antibody (ANA) testing is useful in the diagnosis of systemic connective tissue diseases. A negative ANA test or a positive ANA with a DFS70 pattern makes such a diagnosis unlikely. A positive ANA with a pattern specific for a disease – e.g. centromere – can support a specific diagnosis, as can a positive ANA where further testing shows a positive double stranded DNA (dsDNA) or extractable nuclear antigen (ENA) antibody result, e.g. strong positive speckled ANA with SSA (Ro) and SSB (La) antibodies in a patient with possible Sjogren’s disease.

Often patients present with non-specific symptoms such as muscle/joint aches and fatigue, and an ANA is done “to rule out” an underlying connective tissue disease. Positive ANAs at a titre of 1:80 or higher occur in the normal population at rates of up to 20%, depending on age, and so there is a high chance of false positives in this setting.

Current practice:

At Awanui Labs Auckland, ANA testing is performed using indirect immunofluorescence with Hep20-10. The ANA result will report if the test is positive, the titre, and the pattern. Titre results indicate the degree to which the serum can be diluted before the test is no longer positive; initial screening is done at a titre of 1:80 and subsequent titres are 2-fold, i.e. 1:160, 1:320 etc. This is an interpretative test and minor differences in titre, such as serial results of 1:320 and 1:640, are not significant. Positive ANAs will be sent for ENA/dsDNA testing without the need to specifically request this.

Repeat requests:

We frequently get requests for ANAs that have already recently been performed. Often this is because they were added to a repeat request form. Doing these repeat tests has effects on laboratory workload as well as contributing to patient and requestor uncertainty over what are most often non-significant discrepancies between tests.

Repeating a negative test is unlikely to provide any new information unless symptoms have changed or the result was unexpected. Repeating a positive test is similarly only useful if a different or additional diagnosis is now strongly suspected. Serial ANAs on patients with established diseases are not useful in monitoring or predicting disease activity.

Likewise, serial ENAs are not useful unless new symptoms are present or there is concern about an original negative result. Serial dsDNAs have a role in monitoring SLE disease activity and can be performed without a minimum interval.

New policy:

From now on we will not perform an ANA and/or ENA if we have already done one in the last nine months. We will however store the sample for fourteen days and if a repeat test is still felt to be necessary then the immunology laboratory can be contacted to perform this as an add-on.