In the old days, lupus was feared mostly for its risk of kidney disease. Kidney failure was widely regarded as one of the natural outcomes of lupus. Fortunately, all that has changed, largely due to earlier diagnosis and effective treatment.
Key points
Kidney inflammation can be 'silent'
Blood and urine tests are vital
Kidney biopsy may be needed
Can respond fully to treatment
How does the kidney work?
The kidney is the body's filter. It has the amazing ability to sort out the wanted and unwanted components of the blood, getting rid of waste in the urine. The microscopic individual filters in the kidney are called glomeruli, and it is these delicate filters that can become damaged by inflammation in lupus.
The blood flow through the kidney is immense, and the brilliance of the design of the kidney centres on the close proximity of blood capillaries to the filtering apparatus.
It is not surprising that any interruption of blood flow, for example from thrombosis in Hughes syndrome or from inflammation in lupus, can quickly damage this delicate organ. This damage is irreparable unless treatment is started in good time.
Lupus
In lupus, the kidney can be damaged by two processes: blood clotting and inflammation.
Inflammation of the kidney, if unchecked, goes through four stages seen under the microscope on kidney biopsy:
The first stage is the invasion of the kidney by inflammation cells, a bit like busy bees around a flower.
In the second stage, there is the beginning of damage to the filters (the glomeruli).
In the third stage, there is progressive scarring of the glomeruli.
In the fourth stage there is more scarring of the glomeruli leading, in extreme cases, to a totally scarred, non-functioning kidney.
Obviously, the aim of treatment is to catch the disease before permanent scarring occurs; the good news is that this can usually be achieved.
Tests
By far the most important is urine testing. This usually gives the earliest indication of kidney inflammation. Blood tests monitor potentially more serious kidney disease, while a kidney biopsy gives the most definitive picture of the state of the disease.
Urine testing
Normal urine is clear, with little or no protein content, no infection and no blood cells.
Increasing amounts of protein in the urine is usually the earliest sign of kidney problems. Small amounts are detected by the well known stick testing (eg, Multistix® or Albustix®). When there is heavy protein loss, a 24 hour urine sample is sometimes ordered, to quantify the loss more precisely.
The sample is sent to the laboratory where it is spun down (centrifuged) and inspected under the microscope for blood cells and bacteria.
Blood tests
The three major blood test indicators are urea, creatinine and albumin. When the glomeruli filters are damaged, toxic waste (including the chemicals urea and creatinine) build up in the bloodstream. By contrast, the level of blood protein (albumin) can fall if there is sufficient loss of protein in the urine. These three measurements are part of the routine investigation in lupus.
Renal biopsy
A fine needle biopsy of the kidney is usually recommended in a patient with clear signs of kidney disease, especially in newly diagnosed patients. The aim of the biopsy is to assess the stage of progress of the disease (eg, whether there is any scarring).
In most centres, biopsy is carried out in the X-ray department under screen guidance. The procedure requires a small injection of local anaesthetic in the loin, and has a remarkably safe record. There is a small chance of bleeding into the urine following biopsy and patients are therefore monitored for 24 hours afterwards.
Treatment
The aims of treatment are twofold: to treat the kidney inflammation itself (usually with a combination of steroids and immunosuppressive drugs), and to treat the parallel and related conditions such as raised blood pressure, raised cholesterol and fluid retention.
Fortunately, total kidney failure in lupus is becoming less and less common, as more effective treatments are being developed that can be used early in the disease.
None the less, for those patients requiring dialysis, lupus itself does not present any major additional problems. For those lupus patients coming to kidney transplantation, the outlook is enormously improved. Indeed one of the unexpected findings of the transplant era is that in lupus patients, the disease itself rarely flares after kidney transplant. Some consolation!