| Antinuclear antibodies (ANA) are commonly seen in | | | | (proteins) are usually performed using what is called |
| autoimmune diseases. While a positive ANA is not | | | | the ELISA technique. Antibodies to double-stranded |
| diagnostic of an autoimmune condition, it is seen | | | | DNA are fairly specific for SLE since 70 per cent of |
| often in diseases such as systemic lupus | | | | patients with SLE will have antibodies to |
| erythematosus (SLE), systemic sclerosis, Sjogren's | | | | double-stranded DNA at some point during their |
| disease, polymyositis, and rheumatoid arthritis. | | | | illness. High levels of antibodies to double-stranded |
| Roughly 90 per cent of people with SLE will be ANA | | | | DNA indicate more severe disease and also a higher |
| positive at some time during the course of their | | | | likelihood of kidney disease. Measurements of |
| illness. | | | | antibodies to double stranded DNA change with |
| Who and where the ANA is performed is critically | | | | disease activity so that this measurement should be |
| important. Many expert rheumatologists will have an | | | | repeated for monitoring purposes. |
| office lab that is skilled in performing the ANA test | | | | Anti-Sm antibody (anti-Smith) also is specific for SLE |
| properly. Often, commercial laboratories will have | | | | but is present in only about 30 per cent of patients |
| staff people who are not as experienced in ANA | | | | with the disease. RNP antibodies are seen in patients |
| interpretation. | | | | who have a condition known as mixed connective |
| The ANA is a screening test that is very sensitive | | | | tissue disease (MCTD). |
| for the diagnosis of SLE. On the flip side, though, it is | | | | Antibodies to SSA and SSB (also known as Ro and |
| associated with many false positive test results, | | | | La) can be seen with primary Sjogren's disease and |
| particularly when the ANA is at a low level. Usually, | | | | SLE. |
| ANA levels of 1:80 or lower have less significance | | | | Other useful tests are antihistone antibodies which |
| than higher levels do. However, the interpretation of | | | | are seen with drug-induced lupus, anti-Scl-70 which is |
| the ANA must be made in combination with the | | | | seen in systemic sclerosis, and anti-Jo-1 which is seen |
| patient's history, physical examination, and other | | | | with dermatomyositis. |
| information in order to make a proper diagnosis. | | | | If these specific antibodies are performed as a |
| ANAs also have patterns. These patterns sometimes | | | | quantitative measure, meaning a number representing |
| point towards a diagnosis but are usually not specific. | | | | the amount of antibody is given, then it is often |
| One pattern that seems to be relatively specific is | | | | useful to repeat these tests for monitoring purposes. |
| the anti-centromere pattern which is seen in | | | | Where these more specific tests are performed is |
| conditions such as systemic sclerosis or limited | | | | again important. If done in a laboratory where skilled |
| cutaneous sclerosis. The nucleolar pattern is also | | | | technicians are performing the tests, then the |
| associated with Raynaud's phenomenon and systemic | | | | reliability is much higher than if they are performed in |
| sclerosis. Other patterns such as diffuse or speckled | | | | a general commercial laboratory. Commercial |
| are not very specific. Rarely, a rim or peripheral | | | | laboratories handle a tremendous amount of volume |
| pattern may be seen in patients with SLE. | | | | as well and there have been instances when wrong |
| If a patient has a positive ANA and other clinical | | | | results are given because of a mix up with |
| signs, then more specific laboratory testing is | | | | specimens. |
| required. Tests for these more specific antigens | | | | |