Laboratory tests for Lupus

Dr Babina Thangjam *

Lupus is a difficult disease to diagnose because its symptoms can be vague. And unlike some other diseases, it cannot be diagnosed with a single lab test.

Lupus is an autoimmune disorder that is about 10 times more common in women than in men. In lupus, the immune system, which normally protects against infections, produces an inappropriate immune response against its own tissues. This immune response can cause inflammation and damage to many areas of the body, including the skin, joints, blood vessels, and internal organs, specially kidneys, heart, lungs and the brain.

Some women with lupus may have only vague, mild symptoms while others can experience various troubling symptoms that come and go over time. Women with lupus have a higher risk of other health conditions including heart disease, kidney disease and osteoporosis.

There are several types of lupus; the most common is systemic lupus erythematosus (SLE), which affects many areas of the body. SLE is most frequently seen in people between the ages of 15 and 44, although children, including newborns, and older adults can also have lupus.

CAUSE OF LUPUS

The cause of lupus is not fully understood. It is thought to involve both an inherited component and a trigger that may be related to environmental factors, such as exposure to sunlight, and/or the use of certain medications and viral infections. Lupus may coexist with other autoimmune disorders, some forms of haemolytic anaemia, Hashimoto thyroiditis, and idiopathic thrombocytopenia purpura (ITP).

SIGNS AND SYMPTOMS

Diagnosis of lupus can be extremely challenging, especially because of its wide range of symptoms that can flare up and subside and change over time. A healthcare practitioner must rely on laboratory test results, clinical symptoms, and the person’s medical history for diagnosis. The signs and symptoms may vary from person to person, and by the type of the lupus.

People with lupus may develop a rash, such as:
o A rash resembling a butterfly that appears across the nose and cheeks (malar rash)
o A red rash consisting of round or oval-shaped patches (discoid rash)
o A rash on areas of the skin that are exposed to sunlight (typically the face and extremities)

A rash is typically the only symptom in discoid and subacute cutaneous lupus. People with other types of lupus may have a combination of the following additional signs and symptoms:
o Muscle pain
o Arthritis-like pain in one or more joints (but no or little joint damage)
o Fever
o Persistent fatigue
o Swollen lymph nodes
o Sensitivity to sunlight
o Raynaud phenomenon
o Hair loss
o Anaemia
o Mouth ulcers
o Inflammation and damage to organs and tissues, including the kidneys, lungs, heart, lining of the heart, central nervous system, and blood vessels

Symptoms of lupus may come and go over time and vary from person to person. They may worsen abruptly and die down. Flare-ups may be triggered by changes in someone’s health status, such as physical or emotional stressors, and during pregnancy and after child-birth in women.

LABORATORY TESTS FOR AUTOANTIBODIES

As the diagnosis of lupus is challenging, it is made by clinical evaluation of physical signs and symptoms in combination with tests that can help to confirm the condition or rule out other causes of the person’s signs and symptoms.

The following laboratory tests may be useful in the diagnosis of lupus:
o Anti-nuclear antibody (ANA) – positive in almost all people with SLE, although it can also be positive with those with other autoimmune diseases as it indicates a stimulated immune system
o Anti-Sm antibody (Anti-Smith antibody) – usually seen only in those with SLE
o Anti-double stranded DNA (Anti-dsDNA) – high levels are characteristic of active SLE
o Anti-SSA and Anti-SSB – may also be positive
o Anti-RNP – may be positive
o Anti-chromatin antibodies – may be present in people with SLE who are positive for ANA but negative for anti-dsDNA
o Histone antibodies – for drug-induced lupus
o Antiphospholipid antibodies – such as lupus anticoagulant, anticardiolipin, anti-beta2 glycoprotein I

Other general tests that may be useful for evaluating someone with or suspected of having of having lupus:

o Urinalysis – may show blood, urinary casts, or protein in the urine, which can indicate kidney involvement
o Complete Blood Count (CBC) – may reveal anaemia and decreased numbers of white blood cells and platelets, which can occur with lupus
o Comprehensive Metabolic Panel (CMP) – indicates current status of the kidneys and liver as well as electrolyte and acid/base balance and levels of blood glucose and blood proteins
o Serum Protein Electrophoresis – gamma globulin protein levels are indicative of inflammatory diseases such as SLE
o C-reactive protein (CRP) – another marker of inflammation that may be elevated with lupus

IMPORTANT THINGS TO CONSIDER

There are several things to keep in mind regarding lab tests for lupus:
o Lab tests usually cannot diagnose lupus. Signs and symptoms of the disease are also important.
o When a positive anti-nuclear antibody test (ANA) is accompanied by several other clues that doctors look for in diagnosing lupus, it is often a strong indication to consider lupus.
o It is common for positive lab tests to come and go over time. If this happens, it is less likely that one will receive a lupus diagnosis, though still possible.
o It is very common to get different results in different labs.