Low kidney function happens when your kidneys lose their ability to filter waste and excess fluid from your blood efficiently. Globally, about 788 million adults have some degree of chronic kidney disease, with an overall prevalence of roughly 14%. The causes range from common chronic conditions like diabetes and high blood pressure to genetic disorders, medications, and physical blockages in the urinary tract.
How Kidney Function Is Measured
Doctors assess kidney function using a number called your estimated glomerular filtration rate, or eGFR. This measures how well your kidneys filter blood, expressed in milliliters per minute. A normal eGFR is 90 or above. Between 60 and 89 suggests early kidney disease. Once it drops below 60, you’re in moderate to severe territory, and below 15 is considered kidney failure.
The five stages of chronic kidney disease map directly to these ranges. Stage 1 (eGFR 90+) means there may be kidney damage, such as protein in the urine, but filtering still works normally. Stage 2 (60 to 89) is mild loss. Stage 3 is split into 3a (45 to 59) and 3b (30 to 44), covering mild-to-moderate and moderate-to-severe loss. Stage 4 (15 to 29) is severe, and Stage 5 (below 15) means the kidneys can no longer sustain life without dialysis or a transplant.
Diabetes: The Leading Cause
Diabetes is the single biggest driver of low kidney function. In the United States, roughly 1 in 3 people living with diabetes develop diabetic kidney disease. The damage starts with blood sugar. Persistently high glucose levels injure the tiny blood vessels inside the kidneys that are responsible for filtering waste. As those vessels deteriorate, the kidneys become less efficient and protein starts leaking into the urine.
The process feeds on itself. Damaged kidneys contribute to high blood pressure, and high blood pressure raises the pressure inside the kidney’s filtering units, accelerating further damage. This cycle is why blood sugar control and blood pressure management are treated as inseparable goals in people with diabetes.
High Blood Pressure
Even without diabetes, high blood pressure is a major cause of kidney decline. Your kidneys have a built-in protection system: small blood vessels at the entrance to each filtering unit automatically tighten or relax to keep internal pressure stable, regardless of what your overall blood pressure is doing. This is called autoregulation.
When blood pressure stays elevated for years, those protective vessels slowly harden and stiffen. The process is gradual. In most people with uncomplicated high blood pressure, kidney function declines slowly over decades without obvious symptoms. But once the protective vessels are damaged, they can no longer shield the delicate filtering tissue from high pressure. At that point, kidney damage accelerates. In cases of very severe or “malignant” hypertension, the injury is far more acute, with rapid destruction of blood vessel walls and filtering units.
Inflammation and Autoimmune Disease
The kidney’s filtering clusters, called glomeruli, can become inflamed through several pathways. This group of conditions, collectively called glomerulonephritis, is a significant cause of kidney function loss.
Infections are one trigger. Strep throat, for instance, can lead to kidney inflammation a week or two after the infection clears, as antibodies produced against the bacteria accumulate in the kidney filters. Hepatitis B, hepatitis C, and HIV can also inflame kidney tissue directly.
Autoimmune diseases are another major category. Lupus can attack the kidneys along with the skin, joints, heart, and lungs. IgA nephropathy occurs when a specific type of antibody builds up in the kidney filters over time, gradually impairing their function. A rarer condition called Goodpasture’s syndrome causes the immune system to produce antibodies that target tissue in both the lungs and kidneys simultaneously.
Vasculitis, a group of diseases that inflame blood vessels throughout the body, also damages the kidneys. Conditions like granulomatosis with polyangiitis affect the small and medium blood vessels supplying the kidneys, lungs, and upper airways.
Genetic Causes
Polycystic kidney disease (PKD) is the most common inherited cause of low kidney function. In the dominant form, which runs in families and typically shows up in adulthood, mutations in either of two genes cause thousands of fluid-filled cysts to develop throughout the kidneys. These cysts gradually crowd out healthy tissue, disrupting normal filtering. The recessive form, caused by a different gene mutation, is rarer and usually appears in infancy or childhood.
The proteins produced by these genes are involved in chemical signaling between cells. When the genes are faulty, the signals that guide normal kidney development and organization go wrong, and cyst formation begins. Over time, the kidneys can grow several times their normal size while losing function steadily.
Medications and Toxins
Drug-induced kidney injury accounts for an estimated 14% to 26% of acute kidney injury cases in adults. The kidneys are especially vulnerable to toxic substances because they filter the entire blood supply repeatedly throughout the day, concentrating whatever is in it.
Common culprits include over-the-counter pain relievers like ibuprofen and naproxen, which can reduce blood flow to the kidneys when used frequently or at high doses. Certain antibiotics are known to cause direct damage to the kidney’s tubular cells. Contrast dyes used in imaging scans, particularly when delivered in high doses through arteries, are another recognized cause. Cancer chemotherapy drugs and immunosuppressive medications also carry kidney risks.
The damage may be temporary if the offending drug is stopped quickly, but prolonged or repeated exposure can cause lasting harm. People who already have reduced kidney function, are dehydrated, or are taking multiple kidney-stressing drugs at once face the highest risk.
Physical Blockages
When urine can’t drain properly, it backs up toward the kidneys and causes swelling, a condition called hydronephrosis. If the blockage isn’t relieved, the sustained back-pressure can permanently damage kidney tissue and eventually lead to kidney failure.
The most common physical causes of urinary obstruction include:
- Kidney stones that lodge in the ureter, the tube connecting the kidney to the bladder
- Enlarged prostate (benign prostatic hyperplasia), which compresses the urethra
- Scar tissue in the ureters or urethra from previous infections, surgeries, or injuries
- Nerve damage affecting the muscles that control bladder emptying
Cancers in or near the urinary tract, including bladder, prostate, cervical, colon, ovarian, and uterine cancers, can also press on the ureters or urethra and block urine flow.
Heart Failure
The kidneys and heart are tightly linked. When the heart can’t pump effectively, the kidneys receive less blood flow, which reduces their ability to filter waste. This triggers a hormonal cascade: the body’s fluid-retention systems ramp up, sodium and water accumulate, congestion worsens, and kidney function drops further.
For a long time, low cardiac output was considered the primary reason kidneys suffered during heart failure. More recent understanding has shifted this view. In most patients with acute heart failure, the dominant problem isn’t insufficient blood flow to the kidneys but rather venous congestion, the buildup of pressure in the veins draining the kidneys. Only a small subset of patients in or near cardiogenic shock experience kidney decline driven primarily by low forward blood flow.
Dehydration and Muscle Injury
Severe dehydration reduces the volume of blood reaching the kidneys, which can trigger acute kidney injury. This is usually reversible with fluid replacement, but repeated or prolonged episodes can cause lasting damage, especially in people whose kidneys are already compromised.
A more dramatic form of acute injury occurs with rhabdomyolysis, the rapid breakdown of muscle tissue. When muscle cells rupture, they release a protein called myoglobin into the bloodstream. In large quantities, myoglobin overwhelms the kidneys. It forms obstructive clots inside the kidney’s tiny tubules, directly damages tubular cells, and causes blood vessels within the kidney to constrict. Dehydration significantly increases the risk of kidney injury during rhabdomyolysis because concentrated urine makes it easier for myoglobin to form those obstructive clots. Causes of rhabdomyolysis include crush injuries, extreme exercise, prolonged immobilization, and certain medications.
Why Multiple Risk Factors Compound
Many people with low kidney function don’t have a single cause but a combination. Someone with diabetes who also takes anti-inflammatory painkillers regularly and has mildly elevated blood pressure faces compounding threats to their kidneys from three directions simultaneously. Each condition independently damages the kidney’s filtering system, and together they erode function faster than any one cause would alone. This is part of why kidney disease often progresses silently for years: no single factor seems severe enough to raise alarm, but the cumulative effect steadily reduces the kidneys’ capacity until symptoms finally appear.