Systemic lupus erythematosus (SLE), the most common form of lupus, affects the skin, blood vessels, organs, joints and other body parts. Cutaneous lupus erythematosus targets the skin with chronic inflammatory sores. Photosensitive skin and the rashes are prominent characteristics of this disease. Drug-induced lupus is a potential side effect of several drugs used to treat chronic conditions. When the drug is discontinued, the symptoms disappear. 

The most common symptoms of lupus include:

• Fatigue
• Hair loss
• Mouth ulcers
• Discoid rash – red, disc-shaped scaly patches 
• Seizures, psychosis and other neurological disorders
• Joint pain, swelling and stiffness in more than one location
• Photosensitive skin lesions that become worse with sun exposure
• Malar rash - a butterfly-shaped rash over the cheeks and bridge of the nose
• Fingers and toes that become blue or pale in cold weather or in stressful environments

Making a lupus diagnosis is difficult because there is no definitive laboratory test to validate that an individual has the disease. Lupus is sometimes mistaken for rheumatoid arthritis, another connective tissue disease. Unlike other chronic diseases, the symptoms differ from patient to patient, mimic other diseases and vary in intensity and duration. Most people with lupus have mild symptoms with occasional episodes where the signs and symptoms flare, or increase, in intensity. When the flare ends, the symptoms can diminish or disappear until the next flare. Physicians use a combination of tests and symptoms to reach a conclusive diagnosis.

A complete blood count measures red blood cells, white blood cells, platelets and serum. Lupus patients will test on the low end for these numbers. An abnormally low white blood cell count makes individuals more susceptible to anemia. A decrease in platelets can cause bruising and nosebleeds. Physicians use C-reactive protein, erythrocyte sedimentation rate and other blood tests to measure inflammation in the body. 

Urine tests aid in the diagnosis, early detection and treatment of lupus nephritis, one of the most serious complications of SLE. Nephritis, inflammation of the kidneys, can cause hypertension, protein in the urine and acute or end-stage renal failure. Physicians monitor the level of protein in the urine to gauge the success of therapeutic interventions. 

Antibody tests measure the level of auto-antibodies. Patients with autoimmune diseases have higher levels of auto-antibodies than the general population. The antinuclear antibody blood (ANA) test and anti-extractable nuclear antigen (anti-ENA) test are used to analyze antibodies in the serum. The ANA is sensitive, but not conclusive, for lupus. Physicians will use a positive ANA test and three or more symptoms, such as kidney, joint and skin involvement, to make a conclusive diagnosis.