New Tests for Lupus Kidney Disease?
- Urinary lipocalin-2 is associated with renal disease activity in human lupus nephritis
- Arthritis & Rheumatism, Volume 56, Issue 6, June 2007, pp. 1894-1903
What is the topic?
Anti-dsDNA antibodies are known to contribute to inflammation and this can lead to an increase in specific proteins that can be detected in the blood or urine. One of these compounds is a protein called lipocalin-2, which can be measured in urine samples. In several studies it appeared that high levels of lipocalin-2 in the urine could be an early predictor of kidney damage; these studies, however, were not done on lupus patients, but on patients who suffered kidney problems as a result of infection, surgery, or chemotherapy. One study done on children with lupus reported a correlation between urinary lipocalin-2 and kidney disease.
What did the researchers hope to learn?
The researchers wanted to find out if there was an association between urinary lipocalin-2 and lupus-related kidney disease. If so, could urinary lipocalin-2 serve as a helpful test to identify lupus patients at risk for serious lupus nephritis (LN) and/or as an advance warning sign of an oncoming flare?
Who was studied?
The researchers studied 70 lupus patients from three medical centers in New York City; 32 of these patients had active kidney disease, while the other 38 did not. The lupus patients were predominantly Hispanic (56%) and African American (41%), reflecting the populations served by the urban medical centers. They also included 13 healthy volunteers who didn’t have lupus in order to compare the results to what would be expected in healthy people.
How was the study conducted?
The researchers tested the levels of lipocalin-2 in urine samples and blood samples from each of the patients. They also collected information from all of the lupus patients about the medications they were taking, and used a number of other tests to determine the level of lupus activity in each patient. A number of the patients had previously undergone kidney biopsies, and these were examined as well. The researchers compared and analyzed all of this information to see how they related to the level of lipocalin-2 in the urine.
What did the researchers find?
The researchers found significantly higher levels of lipocalin-2 in the urine of lupus patients with active kidney disease than in the urine of the other lupus patients or the controls -- and the more active the kidney disease, the higher the levels of urinary lipocalin-2. They also noted that higher levels of lipocalin-2 in the urine correlated with evidence of lupus kidney disease but not with other (non-kidney) lupus activity. There was no significant difference in the levels of lipocalin-2 found in the blood samples of the patients with kidney disease so only the urine test seemed to be useful. The researchers took this as further evidence that higher levels of lipocalin-2 in the urine probably resulted from inflammation in the kidneys, and not some other reason. Based on all of these findings, the researchers concluded that urinary lipocalin-2 is a promising potential test for lupus-related kidney disease, and call for additional studies to investigate that possibility further.
What were the limitations of the study?
This research suggests an association between levels of lipocalin-2 in the urine and lupus-related kidney disease, but it doesn’t provide any clue as to whether lipocalin-2 may be contributing to disease activity or just resulting from it.
Also, with the exception of only two patients, all of the lupus patients in this study were either African American or Hispanic. Though both of these ethnic groups are considered to be at high risk for lupus and for severe lupus-related kidney disease, the lack of Caucasians, Asians or other ethnic groups in the study population makes it difficult to draw conclusions from this study that could apply to all lupus patients. Further studies that would include many more patients and also be more representative of the population at large are needed to see if these findings about lipocalin-2 can have broader application. Ideally, those studies would be designed to have kidney biopsies performed in conjunction with lipocalin-2 levels; this would enable researchers to better track the correlation between urinary lipocalin-2 levels and different stages of kidney disease.
What do the results mean for you?
When lupus affects the kidneys, disease activity and damage can occur before symptoms show up, but there are still no specific and reliable indicators for this undetected activity. If lipocalin-2 levels in the urine prove to be an early signal that kidney damage is occurring, doctors might know to begin treatment sooner in attempts to prevent both short- and long-term consequences.