Diagnosing lupus is difficult because signs and symptoms vary considerably from person to person. Signs and symptoms of lupus may vary over time and overlap with those of many other disorders.
No one test can diagnose lupus. The combination of blood and urine tests, signs and symptoms, and physical examination findings leads to the diagnosis.
Blood and urine tests may include:
- Complete blood count. This test measures the number of red blood cells, white blood cells and platelets as well as the amount of haemoglobin, a protein in red blood cells. Results may indicate you have anaemia, which commonly occurs in lupus. A low white blood cell or platelet count may occur in lupus as well.
- Erythrocyte sedimentation rate. This blood test determines the rate at which red blood cells settle to the bottom of a tube in an hour. A faster than normal rate may indicate a systemic disease, such as lupus. The sedimentation rate isn’t specific for any one disease. It may be elevated if you have lupus, an infection, another inflammatory condition or cancer.
- Kidney and liver assessment. Blood tests can assess how well your kidneys and liver are functioning. Lupus can affect these organs.
- Urinalysis. An examination of a sample of your urine may show an increased protein level or red blood cells in the urine, which may occur if lupus has affected your kidneys.
- Antinuclear antibody (ANA) test. A positive test for the presence of these antibodies — produced by your immune system — indicates a stimulated immune system. While most people with lupus have a positive ANA test, most people with a positive ANA do not have lupus. If you test positive for ANA, your doctor may advise more-specific antibody testing.
If your doctor suspects that lupus is affecting your lungs or heart, he or she may suggest:
- Chest X-ray. An image of your chest may reveal abnormal shadows that suggest fluid or inflammation in your lungs.
- Echocardiogram. This test uses sound waves to produce real-time images of your beating heart. It can check for problems with your valves and other portions of your heart.
Lupus can harm your kidneys in many different ways, and treatments can vary, depending on the type of damage that occurs. In some cases, it’s necessary to test a small sample of kidney tissue to determine what the best treatment might be. The sample can be obtained with a needle or through a small incision.
Skin biopsy is sometimes performed to confirm a diagnosis of lupus affecting the skin.
Criteria For Lupus Diagnosis
The American College of Rheumatology (ACR) has devised certain classification criteria, and four or more of these criteria must be present for a classification of lupus. Although these criteria are currently being updated, they are believed to be about 90% effective. The ACR criteria include malar rash; discoid rash; photosensitivity (development of a rash after sun exposure); oral or nasal ulcers; arthritis of multiple joints; serositis: (inflammation of the lining around the lungs or heart); kidney disease indicated by protein or casts in the urine; neurological disorders such as seizures and psychosis; and blood disorders such as hemolytic anemia, leukopenia, and lymphopenia.
Other signs that are common but not included in the classification criteria are hair loss or breaking, especially around the forehead, and Raynaud’s Phenomenon, a two- or three-colour change of the fingertips upon cold exposure.
Although no one symptom qualifies someone as having lupus, certain clinical techniques can be used to narrow down the diagnosis. For example, a test for antinuclear antibodies (ANAs) in the blood is probably the first tool a physician will use. A positive ANA test does not necessarily mean that someone has lupus; in fact, one out of five normal women has a positive ANA. However, a negative ANA test greatly reduces the suspicion.