DEAR DR. ROACH: I have lupus, so my kidneys and other organs are always of concern. After having chronic urinary tract infections for about two years, I was referred to a nephrologist for further testing, and was diagnosed with stage 4 kidney disease. My creatinine level in February was 2.35.

However, when I went back three weeks later to discuss biopsy, a new lab report suggested that the disease had reversed. The creatinine was back down to my normal, around 1.31. Other lab reports in the past had indicated kidney malfunction as well, so while I was not surprised at the disease diagnosis, I was surprised at the reversal. Is this reversal normal at stage 4? I had not been given any changes in medications or diet during the three-week period. — D.R.

ANSWER: Creatinine is a substance in the blood, a waste product of normal muscle turnover. It is removed by the kidney, and it is a pretty good, but not perfect, measurement of kidney function. If kidney function is poor, the creatinine will rise. However, people with more muscle to begin with will have creatinine levels a bit higher.

Some medications, especially ACE inhibitors, increase the creatinine level while still protecting the kidney. Also, changes in fluid status will affect the creatinine. People who get too dry and volume-depleted will have a bump in their creatinine (the bump will be larger in people who already have some kidney malfunction). Because of this, it’s the overall trend that is important, and a single elevated number may or may not be the beginning of a trend, which is why the nephrologist (kidney specialist) wisely rechecked it before performing an invasive procedure like a biopsy. I think the 2.35 number was a bump, perhaps from being dry. Lab errors are rare.

You are absolutely right that people with lupus need to be concerned about kidney function. A biopsy may be appropriate for a sudden increase in the creatinine, but it must be confirmed by a second test on a different day.

DEAR DR. ROACH: I have had several bouts with iritis over the years. My ophthalmologist requested bloodwork by my general physician, and I tested positive for HLA-B27. I am not sure what that actually means. My physician said it has to do with inflammation and arthritis. But he didn’t suggest more tests or treatment. If this is the basis for the iritis, is there anything I need to be doing to prevent future episodes? Could you explain exactly what ”HLA-B27” means? — B.C.

ANSWER: Iritis, also called ”anterior uveitis,” is inflammation of the iris, the colored structure of the eye. It causes pain and redness, and may cause some loss of vision. It isn’t one disease: It can happen by itself or in association with other systemic diseases. Three common and feared systemic diseases that are associated with uveitis are ankylosing spondylitis, reactive arthritis and inflammatory bowel disease.

The human leukocyte antigens (HLA) are molecules on our cell surfaces that allow the immune system to distinguish self from nonself. If a cell is recognized as nonself (such as a foreign invader), it is attacked by the immune cells.

HLA-B27 is a family of these molecules. It is associated with autoimmune disease. Only about 6 percent of North Americans have HLA-B27, but 90 percent of people with ankylosing spondylitis and reactive arthritis are HLA-B27-positive. The body’s immune system can be the cause of the damage to the eye, joints and gut. I am guessing your ophthalmologist and physician may look for evidence of joint or gut disease, even if you don’t have symptoms now.

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