I came across the following information. The website I used is provided at the end.
How is Lupus Diagnosed?
Very slowly and with great difficulty in many cases yet surprisingly quickly in others. Lupus can present in a bewildering number of ways, even to the extent of mimicking other diseases such as RA and MS. With the variety of presentations, lupus is difficult to diagnose and it can be overlooked, often for years, unless the doctor or consultant is alert to its possibility. Many a time the patient has been told "it's all in your mind". A further problem the patient faces is that she or he can look quite well, e.g. "healthy red cheeks" are often in evidence. It is recommended that the patient keep a symptom log or journal as regularly as possible to help in diagnosing and understanding the course of disease. [NOTE: an excellent symptom journal is available through the LFA.]
Doctors will typically rely on lab tests for complete diagnosis. Unfortunately, how each doctor interprets these tests is highly variable and leads to some cases taking years to diagnose.
Basic lab tests should include a CBC with differential, blood chemistries/analyses (SMAC), ESR and urinalysis. Abnormal CBC results may include thrombocytopenia, leukopenia or lymphocytopenia, and/or anemia. It's not uncommon for there to be long-standing, slightly-low WBC's and RBC's. While a single such result might be dismissed as insignificant, long-standing results like these can be significant. Thus, making a graph of these lab results can be a very important tool to aid in diagnosis. 
There may also be an elevated ESR or C-reactive protein which merely indicates that an inflammatory process does exist. Finally, blood chemistries and a urinalysis are important to check for major organ involvement (such as kidney, liver and the thyroid gland). Signs of kidney involvement would include an elevated BUN and creatinine, or the presence of protein in the urine. Blood chemistries which evaluate liver function include AST, ALT, bilirubin, alk. phos. and GGT. Thyroid studies include the T3, T4, Free T4 and TSH.
A biopsy may be performed on a skin rash, mouth ulcer, or if there is a major organ involvement (such as the kidney), on the affected organ.
Lab tests for specific antibodies should also be performed. Most general practitioners will run only an ANA to start with, then if that comes back positive and symptoms of lupus are present, make a referral to a rheumatologist. However, a negative ANA does not preclude referral to a rheumatologist if symptoms persist.
The following are some of the standard tests which most rheumatologists run when lupus is suspected. These include:
- The ANA (antinuclear antibodies) which are considered the cornerstone of lupus diagnosis as they are present at some point in 95-98% of patients with lupus.
- The anti-dsDNA found in 50% of patients with lupus. Anti-dsDNA is so rarely present in patients without SLE that its presence is generally considered diagnostic for SLE.
- Anti-Ro (SSA) which is commonly found in cases of ANA-negative lupus and may indicate secondary Sjogren's Syndrome, and anti-La(SSB) which occurs mainly with primary Sjögren's Syndrome.
- Anti-Sm which is seen in few lupus patients, but when presentcan help confirm the diagnosis.
- The anti-RNP which may indicate mixed connective tissue disease (MCTD) at high levels, or confirm a lupus diagnosis at low levels.
- Anticardiolipins and the lupus anticoagulant. Since1/3 of SLE patients test positive for one or all anticardiolipins (IgA, IgG, IgM) and APS is so common among lupus patients, rheumatologists will often run these tests.
- Rheumatoid Factor (RF) which is positive in 80% of those with RA, but only 20-30% of those with lupus. A high RF titre may suggest an RA diagnosis rather than SLE.
- Immune complexes or complements (C3, C4, CH50) which tend to be low when lupus is very active, and can also be an important gauge of disease severity.
Other important lab tests include CPK, PT and PTT. CPK tends to be elevated when there is muscle inflammation as is common with lupus myositis. Also, the PT and PTT tend to be prolonged in those who are positive for the lupus anticoagulant.
When looking at the above test results, it's important to consider them in context with other test results and symptoms. This means borderline and low-positive results may have more significance than they otherwise would. Also, it's important to track trends over a period of time and note whether the results are abnormal but stable, or fluctuating widely. Further, if there is fluctuation, keeping a symptom log may help pinpoint what caused it.
More on Lupus Diagnosis from Dr. Graham Hughes
The following URL is important for understanding different views of how to diagnose Lupus. We recommend reading the contents of this site in addition to the above diagnostic methods. It can be found at http://www.northeastlupus.org.uk/hughfaq.htm
I've heard of Lupus Criteria - what's that?
It's important to distinguish between SYMPTOMS and CRITERIA. The symptoms listed above are what you have. The criteria are what your doctor can use, along with blood tests, to say "Yes, it's Lupus." or "No it's not." or "I don't know yet." You don't have to have all criteria at the same time. Also, some drugs or metabolic disturbances can cause these symptoms and these need to be excluded.
The American College of Rheumatology has drafted a set of 11 criteria to aid in identifying SLE. These criteria do NOT include all of the symptoms of lupus. In fact, some very common symptoms of lupus (such as chronic fevers, fatigue and hair loss) are not included in the criteria because these symptoms are also very common to other conditions. This list is usually undergoing some amount of revision; however, in its present form it's generally accepted as valid by virtually all physicians in the U.S. and elsewhere.
Generally, to be said to have lupus, you must meet 4 out of these 11 criteria. This does not necessarily provide a definitive diagnosis, however. These criteria are weighted. The criteria given the most weight would involve objective data such as laboratory evidence of SLE. The criteria given the least weight would include more subjective information such as rashes and joint pain. Therefore, a person who has a butterfly rash, joint pain and swelling, pleuritis and mouth ulcers MAY indeed have lupus; however, the certainty of the diagnosis is much greater in a person who has a positive anti-dsDNA, leukopenia, kidney disease and arthritis. Generally, the more criteria met, the more certain the diagnosis.
No compulsory criteria must be met to diagnose SLE. In other words, if a doctor or other health care provider says "You can't have lupus, you don't have [insert any symptom here]." then carefully consider if this doctor is the right person to put your trust in for taking care of you, especially if you have presented with many other obvious symptoms.
Skin
- Butterfly rash (lupus rash over the cheeks and nose)
- Discoid rash (a disk-like rash which starts out red and scaly and later scars)
- Sun Sensitivity (rash upon exposure to sunlight; also commonly fatigue and an exacerbation of other symptoms)
- Oral ulcerations (apthous ulcers are large, irregularly shaped erosions which are often, but not always, painless)
Major organs
- Arthritis (inflammation of two or more joints with pain and tenderness, which may feel worse than it appears)
- Serositis (inflammation of the lining of the heart [pericarditis], the lungs [pleuritis], or abdomen)
- Kidney disorder (as evidenced by protein or abnormal sediment in the urine, elevated BUN and/or creatinine, or kidney biopsy)
- Neurologic disorder (as evidenced by seizures or other CNS symptoms which have no other explanation)
Lab Tests
- Blood abnormalities (hemolytic anemia, low white cell counts, low platelet counts)
- Immunologic disorder (as evidenced by a false positive VDRL, positive anti-dsDNA, or positive anti-Sm)
- Positive ANA
It's important to note here that doctors are usually cautious about diagnosing SLE. One major reason is that once diagnosed, an individual may not be able to get health insurance, or may be forced to pay very high rates for it. Also, this is a major illness and doctors hate to scare patients unnecessarily. Even so, few things are more frustrating to a patient than not being diagnosed where lupus seems obvious. Sadly, it does seem that some doctorsare overly cautious about diagnosing this condition. In this instance, patients usually feel like they are not being taken seriously or treated adequately. The result may be needless suffering.
What is a Positive ANA?
This seems to be the most common question, as this is the test in which most general practitioners and internists (that's hospital doctors in UK) put the most faith as a screening test for lupus. For many doctors, the lowest titre at which they will entertain a diagnosis of lupus is 1:640. However, interpretation of the ANA titre is subject to wide variation. Some are diagnosed with SLE with an ANA titre as low as 1:80, and a large number are diagnosed with a level of 1:160. It's important to realize though that what's considered an insignificant level of ANA varies from lab to lab depending on their methods and materials. Also, this test should always be interpreted in light of other lab results and symptoms. It's far from accurate enough on its own to serve as a definitive test for lupus, nor can it be used to accurately determine the severity of the disease. Its main usefulness seems to be more in determining who probably does NOT have lupus. Since approximately 95% of people with lupus test positive for ANA, lupus is unlikely in someone who tests negative for ANAs repeatedly. The ANA titre is frequently positive in several other autoimmune conditions such as MS, Scleroderma and UCTD. It may be positive in Fibromyalgia (FMS) but at this time, FMS is not considered an autoimmune disease by most medical professionals. ANA titres can be weakly positive in as many as 10% of the healthy population. Still, ANA titres above 1:640 virtually always indicate an autoimmune problem.
I have a Positive ANA but I'm told I don't have Lupus
Many patients make the mistake of assuming that because they don't have a lupus diagnosis *now* that they will never get one. A weakly positive titre in an otherwise healthy individual is generally seen as presenting no cause for concern or further testing. However, if there is a positive titre AND there are symptoms and/or other lab tests suggestive of lupus,periodic re-testing and follow-up is advisable. Such testing should probably include (but not necessarily be limited to) an ANA, anti-dsDNA, CBC with differential, SMAC, and urinalysis. How often this re-testing should be done varies. In some individuals, once a year may be sufficient; however, in others (such as is the case with children suspected of having lupus) that may not be nearly enough.
It's not uncommon for it to take many years to secure a definitive lupus diagnosis. This is because at first presentation, the symptoms and lab tests may be very vague. In time though, the picture usually becomes much clearer and a diagnosis is possible. In a very few, no definitive diagnosis is ever possible. Even so, when the physician is pretty sure they are dealing with either lupus or something related to it, most patients can be successfully treated symptomatically. In fact, a successful trial of medication normally used for lupus may in itself help cement a diagnosis.
Can a Lupus Patient have a negative ANA titre?
From 1-5% of lupus patients may have a negative ANA test despite numerous qualifying criteria. Still, in this instance, patients often test positive for anti-Ro (SSA), a type of ANA. Some will also have a positive anti-dsDNA. This is why when the patient is ANA-negative but complaining of lupus-type symptoms it is worthwhile to ask for these two tests.
A similar problem is that of Undifferentiated Connective Tissue Disease (UCTD). This is acase in which many SLE symptoms are present, even a low-positive ANA, but for which the doctor cannot fit the patient to at least 4 of the ACR's SLE Diagnostic Criteria.
Both ANA Neg. SLE (also called sero-negative SLE) and UCTD are very frustrating for the patient as they often feel they are not receiving the same level of care or concern from their doctors that a patient with full-blown SLE would receive.
Finally, there are times when consistent treatment with standard Lupus medications and taking care of oneself can lead to remissions during which ANA titres are much lower or even negative. Doctors (uninformed ones) have been known to mistakenly undiagnose the patient that has been diagnosed for years, sometimes going so far as to remove lupus therapy and putting the patient at great risk.
http://www.ghg.net/schwerpt/ASLFAQ/diag.htm
I thought that this website had a amaging amount of information. I hope it clears things up for you too.
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