Nephritis is inflammation of the kidneys that damages their filtering units, allowing blood and protein to leak into the urine and potentially reducing overall kidney function. It can develop suddenly after an infection, build gradually from an autoimmune condition like lupus, or appear as a reaction to certain medications. Left untreated, some forms of nephritis progress to permanent kidney damage, while others resolve on their own.
How Kidney Inflammation Works
Your kidneys filter blood through tiny structures called glomeruli, each containing a mesh-like barrier that lets waste and water pass through while keeping blood cells and proteins in. In nephritis, that barrier gets damaged. The immune system sends inflammatory cells, including T cells and macrophages, to the site. Clotting pathways activate, creating tiny blood clots within the kidney’s filtering units. The result is a barrier full of holes and blockages that can no longer do its job properly.
The damage can happen through several routes: immune complexes (clumps of antibodies and foreign material) lodging in the filter, the body’s own immune system mistakenly attacking kidney tissue, direct infection of kidney cells, or a toxic reaction to drugs. Regardless of the trigger, the downstream effect is the same. The kidneys lose their ability to regulate fluid balance, filter waste, and control blood pressure.
Main Types of Nephritis
Nephritis isn’t a single disease. It falls into a few broad categories based on which part of the kidney is inflamed.
- Glomerulonephritis targets the glomeruli, the kidney’s filtering clusters. This is the most commonly referenced form and can be triggered by infections, autoimmune diseases, or genetic conditions. It accounts for roughly 10% of all patients who eventually require dialysis.
- Interstitial nephritis affects the tissue surrounding the filtering units rather than the filters themselves. Drug reactions are the leading cause. Anti-inflammatory painkillers (NSAIDs) account for 44% of drug-induced cases, antibiotics for about 33%, and acid-reducing medications (proton pump inhibitors) are an increasingly common trigger. More than 250 drugs have been linked to this type.
- Pyelonephritis is a bacterial kidney infection, usually starting in the bladder and traveling upward. It causes kidney inflammation alongside infection symptoms like fever and flank pain.
- Lupus nephritis occurs when the immune system attack of lupus extends to the kidneys. It’s classified into six stages (Class I through VI) based on how much of the kidney tissue is involved, ranging from minimal immune deposits to advanced scarring of more than 90% of the filtering units.
Symptoms to Recognize
Nephritis often announces itself through visible changes in urine. Pink or cola-colored urine signals blood leaking through damaged filters. Foamy or bubbly urine suggests excess protein escaping into the urine. You may also notice you’re urinating less than usual.
Beyond urine changes, common symptoms include swelling in the face, hands, feet, and abdomen from fluid your kidneys can’t clear. High blood pressure develops because the kidneys lose their ability to regulate fluid volume. Fatigue, nausea, vomiting, and muscle cramps can follow as waste products build up in the bloodstream. Some people have no obvious symptoms at all in early stages, with the condition only showing up on routine blood or urine tests.
Nephritic vs. Nephrotic Syndrome
These two terms sound nearly identical but describe different patterns of kidney damage. Nephritic syndrome involves blood in the urine, rising blood pressure, reduced urine output, and moderate protein loss. It typically signals active inflammation and tends to carry a more serious prognosis.
Nephrotic syndrome, by contrast, is defined by heavy protein loss (more than 3 grams per day), low blood albumin levels (below 3.0 g/dL), and significant swelling. Blood in the urine is less prominent. The distinction matters because it points toward different underlying causes and different treatment approaches. Some conditions can present with features of both.
How Nephritis Is Diagnosed
Diagnosis usually starts with a urine test looking for blood and protein, neither of which should be there in significant amounts. You may be asked to collect all your urine over 24 hours to measure exactly how much protein is leaking. A blood test checks creatinine and urea nitrogen levels, both waste products that rise when kidney filtering slows down. Low albumin in the blood is another red flag, since it means protein is being lost through the kidneys faster than the body can replace it.
When these tests point to nephritis, a kidney biopsy often follows to identify the exact type and severity. A needle is inserted through the skin into the kidney to collect a small tissue sample, which is examined under a microscope. This step is particularly important because different forms of nephritis require very different treatments, and the biopsy is the most reliable way to tell them apart.
Treatment Approaches
Treatment depends entirely on the type and severity of nephritis. Post-infection glomerulonephritis, the kind that follows a strep throat, often resolves on its own with supportive care. Drug-induced interstitial nephritis improves once the offending medication is stopped. Pyelonephritis requires antibiotics to clear the underlying infection.
Autoimmune forms like lupus nephritis are more complex. Treatment typically involves two phases: an induction phase to bring the inflammation under control, followed by a maintenance phase to prevent flares. Both phases use medications that suppress the overactive immune system, combined with steroids that are gradually tapered down over months. Current guidelines recommend maintenance therapy for at least three years. For lupus nephritis specifically, two newer targeted therapies received FDA approval in 2020 and 2021, offering additional options for patients who don’t respond fully to standard treatment.
Blood pressure control is a cornerstone of treatment across all types. Keeping blood pressure in a healthy range protects the remaining kidney function and slows further damage. Medications that block the renin-angiotensin system are commonly used because they both lower blood pressure and reduce protein leakage from the kidneys.
Long-Term Outlook by Type
Prognosis varies dramatically depending on the specific form of nephritis. At one end of the spectrum, post-streptococcal glomerulonephritis progresses to chronic kidney disease in only 1 to 2% of cases. IgA nephropathy, one of the most common forms worldwide, leads to kidney failure in about 10% of patients over 10 years.
Other types carry a heavier burden. Membranous nephropathy progresses to kidney failure in 20 to 30% of patients within a decade. Lupus nephritis reaches that point in about 20%. The most aggressive form, rapidly progressive glomerulonephritis, can destroy kidney function within weeks or months if untreated, with roughly 90% of patients progressing to kidney failure. Early detection and treatment make a significant difference in nearly every type.
Dietary Changes That Help
When nephritis leads to reduced kidney function, dietary adjustments become an important part of management. Sodium is the first target: federal guidelines recommend staying under 2,300 milligrams per day, but many people with kidney inflammation need to go lower. Cutting back on packaged foods, processed meats, and fast food makes the biggest impact. Reading nutrition labels helps: a “% Daily Value” of 20% or more means the food is high in sodium, while 5% or less means it’s low.
Protein intake may need to be moderated so the kidneys don’t have to work as hard to clear protein waste. This doesn’t mean eliminating protein, but shifting toward leaner sources and incorporating more plant-based options. Phosphorus and potassium, two minerals the kidneys normally regulate, can build up when filtering slows. Avoiding processed foods with added phosphorus (look for “PHOS” on ingredient lists) and managing potassium-rich foods through portion control and preparation techniques like boiling can help keep levels in check.
Fluid intake sometimes needs to be restricted as well, since damaged kidneys can’t remove excess water efficiently. The specifics vary by individual, so the right dietary plan depends on how much kidney function has been affected and which minerals are out of balance.