Tests and diagnosis of Lupus
There is no specific test for the diagnosis of lupus and could take months or years to detect it. For its diagnosis, the following are performed a medical history, a complete physical examination and blood tests.
Laboratory tests for autoimmune disorders. Patients with systemic lupus erythematosus (SLE) have several antibodies and other immunological alterations, the presence of which is monitored using blood tests:
- Antinuclear antibodies: They are usually present in the majority of autoimmune diseases and generally very high in SLE.
- Anti-DNA antibodies: They are specific for SLE and increase when there is flare-up of the disease.
- Anti-Sm (Smith) antibodies: Although they are also specific for SLE, they appear in low percentage (10%) of patients.
- Anti-Ro, anti-La and anti-RNP antibodies: They appear in some patients with SLE, but also in other related autoimmune diseases.
- Anti-phospholipid antibodies (anticardiolipin, anti-beta-2-glycoprotein I and lupus anticoagulant antibodies): They appear in approximately 30% of patients with SLE, and their presence increases the risk of developing blood clots, and complications in pregnancy.
- Rheumatoid factor: Although it is more typical of rheumatoid arthritis (another autoimmune disease that mainly affects the joints), it can also appear in patients with SLE.
- Complement levels (C3, C4, CH50): They decrease when there is a flare-up of the disease.
- Given that the anti-DNA antibodies increase and the decrease in the complement levels are indicative of flare-ups of the disease, their determination is usually repeated periodically (every few months).
Skin biopsy. In order to diagnose cutaneous lupus erythematosus (CLE), samples of skins tissue are analysed under a microscope (histology study), as well as a direct immunofluorescence study. The diagnosis of CLE is based on three points:
- Clinical findings. That is to say, the appearance of the lesions. It is important that they are examined by a dermatologist with sufficient experience in CLE because the lesions can easily be confused with the lesions of other more common skin diseases.
- Histology findings. That is to say, the microscopic examination of the skin lesions. It is important that the biopsies are examined by a pathologist expert in skin lesions. The diagnostic characteristics under the microscope are much more likely to be found in the skin lesions specific to CLE than in lesions not specific to CLE.
- Direct immunofluorescence findings. It is a special microscopic examination technique of the skin lesions. This test is often negative, but when it gives positive results it can be very useful for the diagnosis of CLE. It is particularly effective for diagnosing chronic CLE.
Kidney biopsy. In patients with lupus nephritis, the kidney biopsy helps to determine the severity of the inflammation, the extent of the scarring, and to establish the most appropriate treatment.
This test is performed using local anaesthetic. Using a special needle, a very small piece, of about 2-3 cm, of kidney (generally the left one) is removed and analysed under the microscope. It is a straightforward procedure apart from the discomfort of the puncture itself and the complete rest for the first 24 hours. The patient has to lie on his/her back and follow the instructions of the medical team.
As with any other medical procedure there may be complications such as:
- Appearance of blood in the urine in the first 24-48 hours.
- Slight discomfort around the site of the puncture.
- An arteriovenous fistula, which is the communication between an artery and a vein that is generally asymptomatic and cures by itself, although, in some cases, it has to be treated.
- Bleeding around the kidney that very exceptionally requires a surgical intervention, as it normally resolves spontaneously.
In order to reach a firm diagnosis and to perform scientific studies, many doctors used the so-called “classification criteria”, which are clinical manifestations and analytical results common in lupus. The criteria most used are the 11 criteria described by the American College of Rheumatology, of which 4 have to be present simultaneously or over a period of time. However, medical experts can reach a lupus diagnosis if the clinical and laboratory manifestations are very characteristic, although they may not contain these four “criteria”.
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