Lab Testing for Lupus
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Lab Testing for Lupus
(The following information are excerpts taken from an article written by Dr. Michael Lockshin entitled, Laboratory Testing in Lupus.)
Are you confused by the names of the blood tests doctors use to diagnose or monitor lupus? Do you know what the tests mean? If you are confused, perhaps the information below will help:
An antibody is a protein (such as gamma globulin and other globulins) that the body normally makes to defend itself against bacteria (germs), viruses, and other things that cause harm. In lupus, the body mistakenly makes antibodies against a person’s normal tissue.
An antibody is named according to the substance (antigen) which it is made to fight. Thus, an antibody induced by a polio vaccination is called an anti polio virus antibody.
Because the basic abnormality of lupus is an immune system that is in overdrive, most of the tests measure the degree to which the immune system is active.
Other tests measure the function of specific organs such as the kidneys.
ANA, FANA (Common name of test, including synonyms)
Translation of name: (Fluorescent) Anti-Nuclear Antibody
Brief Explanation of what the test is designed to look for: An antibody against the nucleus, or central controlling part of each cell. All organs are made of cells and all cells have nuclei (plural for nucleus). ANAs have four basic patterns describing the way they look under a microscope. The patterns are "diffuse" (the whole nucleus lights up) "peripheral" or "rim" (only the rim around the nucleus does), "speckled" (just what it sounds like) and "nucleolar" (two very specific spots light up).
What a positive test means: Almost all patients with lupus have a strongly positive test (still positive even when diluted more than 100 times, commonly expressed 1:100). Many normal people also have positive tests, usually less strong (diluted ten to 30 times, 1:10, 1:30). The "diffuse" and "speckled" patterns are common in lupus but are also seen in other diseases and in normals; the "peripheral" pattern is relatively specific for lupus. The nucleolar does not often occur in lupus. A positive test means lupus is a possible diagnosis.
What a negative test means: A negative test usually means that a patient does not have lupus, or that lupus is in remission. However, most patients in remission do not have negative ANAs.
anti (ds) DNA antibody
Translation of name: Antibody of Double-Stranded (also called native) Deoxyribonucleic Acid
Brief explanation of what the test is designed to look for: DNA is the major part of the cell nucleus, and is the stuff of which our genes are made. The anti-DNA antibody is usually the reason for the positive ANA. People who have a positive ANA who do not have anti-DNA have antibodies against other parts of the nucleus. Anti-ss-DNA (Single Stranded, or denatured) is less important than anti-ds-DNA.
What a positive test means: An unequivocally positive test in a person with symptoms almost always means lupus is present. The higher the amount, the more likely the disease is active. Rarely, well blood relatives of lupus patients have positive tests, as do some patients with rare other diseases. (There are several ways of expressing a positive test).
What a negative test means: A negative test does not mean that lupus is not present, since other tests can still be positive in a person who has had a positive test, a negative test usually means remission. (See ant-Sm).
Complement, CH 50, C3, C4
Translation of name: Complement is a series of proteins that help antibodies fight antigens: CH 50 refers to the amount of complement necessary to destroy (hemolyse) 50% of red blood cells in an immune reaction. C3 and C4 are the third and fourth complement proteins
Brief explanation of what the test is designed to look for: Complement is used up in immune reactions, such as lupus.
What a positive test means: Low levels of complement mean the body is undergoing a severe immune reaction, primarily in the kidneys. Lupus is one cause, but there are many others. CH 50 is usually 150-300 units. C3 about 80-150 mg/dL, C4 about 15-40 mg/dL.
What a negative test means: Normal levels of complement make lupus inflammatory kidney disease unlikely. Other types of kidney disease, such as leaky kidneys or scarring, can still occur even if complement is normal. Other types of lupus (rash, arthritis, brain disease) do not usually lower complement.
aCL, aPL, lupus anticoagulant, antiphospholipid antibody, a PTT, dRVVT
(Common name of test, including synonyms)
Translation of name: Antibody to CardioLipin, antibody to PhosphoLipid, Activated Partial Thromboplastic Time; Dilute Russell Viper Venom Time
Brief explanation of what the test is designed to look for: Cardiolipin is a phospholipid (a type of fat that contains phosphate). There are many other phospholipids, but cardiolipin is the one most frequently tested. The test can be performed on clotted blood. The lupus anticoagulant test (for antibodies to clotting factors) can be performed only on fresh blood, since it measures the time it takes the blood to clot. Except for the different techniques, the tests measure approximately but not exactly the same things, so it is possible to have a positive aPL test and a negative lupus anticoagulant, and vice versa. The membranes that surround all cells are composed of phospholipids. aPTT and dRVVT are two specific clotting tests used to screen for a lupus anticoagulant antibody.
What a positive test means: An unequivocally and repeatedly positive test means a higher than normal likelihood of developing internal blood clots or problems with pregnancies. Weakly positive tests that come and go are common and generally not important. About 1/3 of lupus patients have either an aPL or lupus anticoagulant test positive. Normal aCL (immunoglobulin G, lgG) is usually under 15 GPL units, for immunoglobulin M (lgM), under 10 MPL units. Normal aPTT is usually under 35 seconds.
What a negative test means: A negative test markedly reduces the likelihood of internal clotting problems or certain types of pregnancy complications.
Urinary protein, proteinuria, albuminuria
(Common name of test, including synonyms)
Translation of name: Self explanatory
Brief explanation of what the test is designed to look for: The kidneys normally do not excrete protein.
What a positive test means: The kidneys that leak protein are abnormal. The more they leak the worse the injury. Normal is under 1/4 gram in 24 hours. Over 4 grams a day is high.
What a negative test means: Kidneys that do not leak protein are usually normal or near normal. Rarely, function can be abnormal even without protein in the urine.
Platelets
Translation of name: A type of blood cell that helps in clotting
Brief explanation of what the test is designed to look for: Platelets are used up in severe clotting and are reduced by antibodies to platelets.
What a positive test means: Low platelets occur for several reasons in lupus. All reasons need to be checked out, since very low platelets are associated with spontaneous bleeding. Normal platelet count is 150,000/cubic mL of blood.
What a negative test means: A normal platelet count means no problems in this system.
The information above are excerpts from a medical article entitled "Laboratory Tests in Lupus" written by Dr. Michael D. Lockshin is Director, Barbara Volcker Center for Women and Rheumatic Disease, Hospital for Special Surgery, Professor of Medicine, Cornell University Medical College, New York, NY.
www.LupusMCTD.com
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