Low kidney function happens when your kidneys lose their ability to filter waste and excess fluid from your blood efficiently. The two most common causes are diabetes and high blood pressure, which together account for the majority of chronic kidney disease cases worldwide. About 14.2% of adults globally have some degree of chronic kidney disease, and the leading risk factors are high blood sugar, high body mass index, and high blood pressure.
Kidney function is measured by how well your kidneys filter blood each minute, expressed as a number called GFR. A normal GFR is 90 or above. Mildly decreased function falls between 60 and 89, moderate loss between 30 and 59, severe loss between 15 and 29, and anything below 15 is considered kidney failure.
How Diabetes Damages the Kidneys
Persistently high blood sugar is one of the most destructive forces your kidneys face. The damage starts at a microscopic level: excess glucose in the bloodstream triggers a chain of metabolic changes inside the kidney’s tiny filtering units. Sugar increases oxidative stress, which injures the delicate cells lining your blood vessels. Over time, this causes inflammation, scarring, and a steady loss of working filters.
Diabetes also disrupts the kidney’s built-in pressure regulation. Healthy kidneys have a mechanism that keeps blood pressure inside their filters stable, regardless of what your overall blood pressure is doing. In diabetic kidney disease, that protective mechanism breaks down. The result is that higher pressures from the rest of your circulation get transmitted directly into the kidney’s fragile filtering structures, accelerating damage. To make matters worse, kidney cells affected by diabetes ramp up their absorption of glucose, which keeps the cycle of sugar-driven injury going even when blood sugar levels elsewhere in the body improve temporarily.
The Role of High Blood Pressure
High blood pressure and kidney disease feed each other in a vicious cycle. When blood pushes through the kidneys at higher-than-normal force, it stretches and damages the walls of the small blood vessels inside each filtering unit. That triggers inflammation and scarring, which reduces the number of functioning filters. As kidney function drops, the kidneys become worse at removing sodium and water, which increases blood volume and drives blood pressure even higher.
This cycle is why many people with kidney disease also have resistant high blood pressure. The kidney damage makes it harder for medications to bring blood pressure down, and the elevated pressure continues to erode kidney tissue. For people who have both diabetes and high blood pressure, the two conditions compound each other’s effects on the kidneys significantly.
Autoimmune and Inflammatory Kidney Disease
Your immune system can attack your kidneys directly. In conditions collectively known as glomerulonephritis, the immune system targets the kidney’s filtering membranes, causing inflammation that disrupts their ability to separate waste from useful proteins and blood cells. The most common form is IgA nephropathy, where a specific type of antibody deposits in the kidney filters and triggers chronic inflammation.
Lupus is another major autoimmune cause. In lupus nephritis, the immune system produces antibodies that attack kidney tissue, leading to inflammation and, in severe cases, permanent scarring. The most aggressive form, called diffuse proliferative nephritis, can cause rapid scarring that progressively and irreversibly reduces kidney function. Treatment focuses on suppressing the immune system to slow or stop the attack, but any scarring that has already formed is permanent.
Genetic Causes
Polycystic kidney disease is the most common inherited cause of kidney failure. It affects roughly 1 in 400 to 1,000 people and causes fluid-filled cysts to grow throughout both kidneys over a person’s lifetime. These cysts slowly expand, crushing and replacing healthy kidney tissue. The kidneys can grow to several times their normal size before function drops noticeably.
The disease is caused by mutations in one of two genes that produce proteins essential to the structure of kidney cells. When those proteins are defective, kidney cells multiply abnormally and secrete excess fluid, forming the cysts. Because the cyst growth is gradual, many people don’t experience symptoms until their 30s or 40s, but the damage has been accumulating since birth.
Medications That Harm the Kidneys
Several common medications can reduce kidney function, sometimes after just short-term use. NSAIDs (ibuprofen, naproxen) are among the most frequent culprits. They work by reducing blood flow to the kidneys, which lowers the filtering rate. Occasional use in a healthy person is generally tolerable, but regular use, especially in someone who already has reduced kidney function, can cause lasting damage.
Other medication categories that can injure kidneys include:
- Certain antibiotics, which can form insoluble crystals in kidney tissue or directly damage the tubules that process filtered fluid
- Lithium, used for mood disorders, which can cause chronic inflammation in kidney tissue over years of use
- Some antiviral drugs, which can crystallize inside the kidneys and block the flow of urine at a microscopic level
- Certain cancer drugs, particularly platinum-based treatments, which are directly toxic to kidney cells
The risk increases when multiple kidney-stressing medications are used at the same time, or when someone is dehydrated, since concentrated drug levels in the kidneys amplify the toxic effects.
Physical Obstructions
Anything that blocks the flow of urine can cause kidney damage by forcing urine to back up into the kidneys, raising internal pressure. In men, the most common cause of obstruction is an enlarged prostate, which squeezes the urethra and makes it difficult for the bladder to empty completely. Kidney stones are another frequent cause, particularly when a stone lodges in the tube connecting a kidney to the bladder.
Damage from obstruction can begin within hours. The backed-up pressure dilates the kidney (a condition called hydronephrosis) and, if it persists for weeks or months, causes the kidney’s internal structures to atrophy. Tissue that was once filtering blood gets replaced by scar tissue. Short-term obstructions are often fully reversible once the blockage is cleared, but chronic obstruction can lead to permanent nephron loss and, eventually, kidney failure.
Infections and Kidney Scarring
A kidney infection, or pyelonephritis, can cause lasting damage if not treated promptly. Bacteria typically travel up from the bladder into one or both kidneys, triggering intense inflammation. A single well-treated infection rarely causes long-term problems, but recurrent infections or a severe infection that goes untreated can scar the kidneys permanently. That scarring reduces the total amount of functional tissue available for filtering, leading to a measurable drop in kidney function over time.
Sudden vs. Gradual Loss of Function
Not all kidney function loss develops slowly. Acute kidney injury is a rapid decline that can happen over hours or days, often triggered by severe dehydration, a sudden drop in blood pressure (from major blood loss or sepsis), or exposure to a toxic substance. The kidneys essentially shut down because they aren’t receiving enough blood, or because something is directly poisoning their cells. The good news is that acute kidney injury is frequently reversible if the underlying cause is corrected quickly.
Chronic kidney disease, by contrast, develops over months to years and is usually not reversible. Its symptoms are subtle at first: fatigue, poor appetite, waking at night to urinate, itchy skin. Many people don’t realize they have it until a routine blood or urine test reveals the problem. A blood test measuring your GFR and a urine test checking for protein leakage (specifically, albumin) are the two main tools for catching kidney disease. A urine albumin level between 30 and 300 mg/g indicates moderate kidney damage, while a level above 300 mg/g signals more advanced disease.
Having one episode of acute kidney injury increases your risk of developing chronic kidney disease later, and people who already have chronic kidney disease are more vulnerable to acute episodes. The two conditions are closely intertwined, which is why even a temporary insult to the kidneys deserves follow-up monitoring.