May. 01, 2010

Urine Protein Indicates Presence of Lupus Nephritis

Urinary TWEAK as a biomarker of lupus nephritis: a multicenter cohort study.
Authors: Schwartz N, Rubinstein T, Burkly LC, Collins CE, Blanco I, Su L, Hojaili B, Mackay M, Aranow C, Stohl W, Rovin BH, Michaelson JS, and Putterman C. (2009).
Arthritis Research & Therapy 11: R143. 

What is the topic?

Lupus nephritis (LN) means that the kidney is inflamed. Currently, most people who are suspected of having LN have to get a kidney biopsy, a procedure in which small pieces of the kidney are removed for study under a microscope. The biopsy shows the type of kidney problem and the extent of the inflammation so that the best treatments can be given. People with LN could benefit if the same information could be gained without a biopsy.

What did the researchers hope to learn?

The researchers hoped to find out if levels of a protein called TWEAK in samples of the urine or blood could be used to diagnose LN.

Who was studied?

People were recruited to participate in the study from across the country, including 30 patients who had kidney biopsies indicating active LN, 49 lupus patients without LN, 28 healthy people, 31 patients with kidney disease because of either diabetes or high blood pressure (renal patients), 79 rheumatoid arthritis (RA) patients, and 25 patients with osteoarthritis (OA).

For some measurements, 13 additional patients with LN were also included.

How was the study conducted?

Each patient provided a morning urine and/or blood sample. 

Levels of TWEAK were measured in the urine (called “uTWEAK”) and blood (called “sTWEAK”). The “s” stands for serum, which is the part of the blood that is left when the red blood cells are removed.

What did the researchers find?

The researchers found that levels of uTWEAK were increased in LN patients compared to other groups, except OA and renal patients. Levels of uTWEAK were similar among the following groups: non-LN lupus patients, RA patients, OA patients, renal patients, and healthy people.

They also found that higher levels of uTWEAK were related to more severe LN and that uTWEAK distinguished between LN and non-LN lupus patients better than antibodies to double-stranded DNA and complement, which are some of the tests that are currently used for this.  

uTWEAK levels were highest during LN flares and were decreased during the 4-6 months before and after a LN flare.

sTWEAK levels were lower in people with lupus than in healthy people. sTWEAK levels were not related to the presence of LN or disease activity and were not as good at identifying lupus as traditional indicators such as antibodies to double-stranded DNA and complement. Therefore, a blood test for TWEAK may not be as useful as a test of urine for TWEAK. Levels of uTWEAK were not compared to overall levels of blood proteins in the urine, which is the traditional way that LN has been diagnosed.

What were the limitations of the study?

This study was larger than many others that have been done looking at urine tests for LN, and it included other groups of people to compare to, but it will still require more studies to be sure of how well this test can predict different aspects of LN and whether it can help in monitoring patients with LN and their responses to treatments.

What do the results mean for you?

The availability of urine tests for LN may mean that a kidney biopsy may one day not be necessary to accurately diagnose LN, select the best treatments, or see how a patient is doing over time. This will be an advantage for people with lupus since a kidney biopsy is an invasive procedure, can sometimes have serious side effects, and is not a practical way to monitor LN disease activity over time.


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