Organ affected: kidneys

Lesson 4 Common questions

Learn some terms used in renal care, how they relate to IgG4-RD kidney involvement, and which changes should prompt clinical follow-up.

Common kidney questions in IgG4-RD

When IgG4-related disease (IgG4-RD) involves the kidneys or the area around them, it is natural to have questions. Such as: “Why did this happen to ME?”

You may wonder what your test results mean, why imaging is needed and what kinds of imaging tests are best, or when a symptom should prompt a call to your care team. And many more.

In this lesson you will find clear answers to common kidney questions in IgG4-RD. It will help you understand what your clinicians are watching for and how kidney-related changes may be managed.

1. What does it mean if IgG4-RD involves my kidneys?

It means IgG4-RD is affecting either the kidney itself or the tubes and tissues around the kidney. The kidney is like a careful filter. It cleans waste from the blood while keeping the things your body still needs. If inflammation enters the kidney’s filter system, or if urine cannot drain normally because a ureter is narrowed, kidney function can be strained.

Some people feel symptoms, such as back or side pain, swelling in the legs, changes in urination, or fatigue. Others feel well, and the problem is found only because blood tests, urine tests, or imaging show a change. That is why monitoring matters. The kidneys can be quiet even when they need help.

Kidney involvement is one of the recognized organ patterns in IgG4-RD, and retroperitoneal disease can narrow the tubes that connect the kidneys to the bladder.¹

2. What is creatinine, and why does my doctor check it?

Creatinine is a waste product that comes from normal muscle activity. Your kidneys remove creatinine from the blood. A blood test can measure how much creatinine is present.

If the creatinine level rises, it may mean the kidneys are not clearing waste as well as expected. But one number never tells the whole story. Creatinine can vary based on age, muscle mass, hydration, medications, and the lab method. Your care team looks at the pattern over time, not just one result.

A helpful way to picture creatinine is to imagine the kidney as a sink drain. Creatinine is like water that should flow through the drain. If the drain is slowed by inflammation, scarring, dehydration, medication effects, or a blockage, the level in the “sink” can rise. Your team’s job is to find out why.

3. What is eGFR?

eGFR stands for estimated glomerular filtration rate. That is a long phrase, but the idea is simple: eGFR is an estimate of how well your kidneys are filtering blood.

The “glomeruli” are tiny filtering units in the kidneys. Think of them as small strainers. The eGFR gives your care team a broad sense of how much filtering power the kidneys have. A lower eGFR can mean the kidneys are under stress or have less filtering ability than expected.

Your eGFR is usually calculated from your creatinine level, along with other information such as age and sex. Because it is an estimate, your doctor will interpret it together with your urine tests, blood pressure, imaging, medications, and IgG4-RD activity.

4. What is hydronephrosis?

Hydronephrosis means swelling of the kidney because urine is backing up. It is not a disease by itself. It is a sign that urine may not be draining normally from the kidney to the bladder.

In IgG4-RD, hydronephrosis can happen when inflammation or fibrosis in the retroperitoneum presses on a ureter. The ureter is the soft tube that carries urine from the kidney to the bladder. If the ureter is squeezed, urine can back up, like water behind a kinked garden hose.

Hydronephrosis is important because pressure can injure the kidney if it is not relieved. Depending on the situation, doctors may treat the inflammation, place a ureteral stent to hold the tube open, place a drainage tube directly into the kidney (this is called a nephrostomy tube), or use a combination of approaches.²

5. What is retroperitoneal fibrosis, and how can it affect the kidneys?

Retroperitoneal fibrosis, often shortened to RPF, means scar-like inflammatory tissue in the retroperitoneum. The retroperitoneum is the deep space in the back of the abdomen, near the aorta, kidneys, and ureters.

Fibrosis means scar-like tissue. In IgG4-RD, fibrosis can form when the immune system’s “repair crew” gets stuck in overdrive. Instead of finishing the repair and stepping away, the repair process keeps building firm tissue. If that firm tissue forms around a ureter, it may squeeze the ureter and slow urine flow.

RPF can be caused by IgG4-RD, but not every case of RPF is IgG4-RD. Other causes can include certain medications, infections, prior radiation or surgery, other inflammatory diseases, and cancer. For that reason, doctors may recommend imaging, blood tests, and sometimes a biopsy to confirm what is causing it. ³

6. What is a ureteral stent?

The ureter is a tube that connects each kidney to the bladder. When hydronephrosis develops, the ureter becomes restricted and blocked by fibrosis. If that occurs, a ureteral stent must be inserted into the ureter to keep the ureter open and maintain normal urine flow from the kidney to the bladder.

A ureteral stent is a small, soft tube placed inside the ureter to help urine drain from the kidney to the bladder. It is not the same as a heart stent, though the idea is similar: it helps keep a narrowed passage open.

A stent may be used when the ureter is narrowed or squeezed and the kidney is swelling from backed-up urine. Some people notice bladder pressure, urinary frequency, blood-tinged urine, or discomfort while a stent is in place. Others tolerate it well. Your urologist can explain what is expected and when the stent should be changed or removed.

A stent treats the drainage problem. It does not treat the immune inflammation by itself. That is why kidney care in IgG4-RD often involves teamwork among rheumatology, nephrology, urology, radiology, and sometimes other specialists.

7. Does a normal blood IgG4 level mean my kidneys are safe?

No. A normal blood IgG4 level does not fully rule out IgG4-RD activity.

Serum IgG4 level means the amount of IgG4 antibody measured in the blood. It can be helpful, but it is not a perfect test. Some people with IgG4-RD have normal IgG4 levels, and some people have high IgG4 levels for reasons other than IgG4-RD. IgG4ward explains that IgG4 is present in everyone’s blood and that some patients with IgG4-RD have normal serum IgG4 concentrations.⁴

>For the kidneys, your team usually looks at the whole picture: creatinine, eGFR, urine testing, complements such as C3 and C4, symptoms, imaging, and sometimes biopsy results. The blood IgG4 number is one clue, not the whole map.

8. Will kidney involvement always cause symptoms?

No. Kidney involvement can be quiet.

This can feel surprising. Many people expect kidney problems to cause pain right away. But the kidneys often do their work silently. You may feel completely normal while a blood test shows a change in creatinine, a urine test shows protein or blood, or an ultrasound or CT scan shows hydronephrosis.

That is why follow-up matters even when you feel well. Regular testing is not just a formality. It is a way of listening to organs that may not speak loudly at first.

9. When should I contact my care team?

Please contact your care team if something feels new, different, or concerning. Your own clinic may give you more specific instructions, and those should come first. In general, kidney-related reasons to call include:

• New or worsening pain in your side, back, or lower belly

• Fever, chills, burning with urination, or signs of infection

• A clear drop in urine amount, or trouble passing urine

• New blood in the urine, or urine that looks cola-colored

• New swelling in the legs, feet, face, or around the eyes

• New shortness of breath, chest discomfort, or sudden weight gain from fluid

• A message from your clinic that creatinine has risen, eGFR has fallen, or imaging shows hydronephrosis

• New symptoms after a ureteral stent, especially fever, severe pain, or inability to urinate

If you have severe pain, high fever, confusion, chest pain, fainting, or you cannot urinate, seek urgent medical care.