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An RPR, rapid plasma reagin, is a blood used in the screening for syphilis. It is similar to the VDRL, venereal disease research laboratory, test. And RPR blood test searches for antibodies that will be present in the blood of patients with syphilis.
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How in This Blood Test Done?
This blood test is done by drawing blood from a vein, typically a vein on the back of the hand or a vein on the inside of the elbow. The health care provider will tie a tourniquet around the upper arm to encourage the vein to swell with blood. They will clean the area with an alcohol swab. They will then carefully insert a needle into the chosen vein. The blood will flow into an airtight tube or vial attached to the other end of the needle. They will remove the tourniquet and once enough blood has flowed into the vial or tube, they will remove the needle. The puncture site will be covered with a small square of sterile gauze or a sterile cotton swab. The patient will be told to apply pressure to the puncture site and elevate the arm. If there is still a little bleeding after a few minutes, the puncture site will be bandaged.
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How Should I Prepare and Does it Hurt?
Most patients will not have to prepare at all. However, those who tend to become woozy after they have blood drawn should bring some orange juice to drink after the blood test. Patients who take any medications or who have any medical conditions should tell their doctor, however, because certain medical conditions can interfere with this blood test and produce a false-positive result.
This blood test is not painful, but there may be some discomfort for some patients. Patients may feel a stinging sensation or prick when the needle is inserted into the vein. After the test is done some patients may feel some temporary throbbing. The area of the puncture may be bruised for a few days after the test is done and this is normal.
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Why is an RPR Performed?
An RPR blood test is primarily done to diagnose syphilis, but it does have other purposes. Patients who have already been diagnosed with syphilis may have this blood test to see how well their syphilis treatment plan is working. Once they are diagnosed, they will be prescribed antibiotics that should decrease the level of syphilis antibodies and this blood test will be able to determine whether these antibodies are actually decreasing. If they are not decreasing the doctor can adjust the patient's treatment plan. If a patient's level of syphilis antibodies is rising or is not changing at all this can indicate a persistent infection and the doctor can adjust the treatment plan.
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A negative result means that the test is normal. However, a negative result does not always mean a patient does not have syphilis because antibodies are not always produced by the body in response to the syphilis bacteria. Because of this, the RPR is not always accurate. False-negative results can occur in the late stages of this disease and in the early stages of this disease. If a false-negative occurs, further testing is often necessary.
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Once this blood test is done and the sample is analyzed, a positive result means the patient has syphilis. If a positive result is present, the diagnosis will be confirmed with a specific syphilis test known as an FTA-ABS. An FTA-ABS will confirm a syphilis diagnosis by distinguishing between other infections and syphilis. During the early and later stages of the disease and RPR is not nearly as sensitive as it is during the middle stages of this disease. During the middle stages this blood test is almost 100 percent accurate. Certain medical conditions may cause a false positive test result and these include HIV, systemic lupus erythematosus, Lyme disease, malaria, and certain forms of pneumonia.
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Medline Plus. (2009). RPR Test. Retrieved on February 23, 2010 from Medline Plus: http://www.nlm.nih.gov/medlineplus/ency/article/003533.htm
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Phlebotomy Tray: Bubbels – Wikimedia Commons