Where your kidneys are
Most adults have two kidneys, each about the size of a fist, located on either side of the spine just below the rib cage. Each kidney contains roughly one million nephrons — the microscopic filtering units that do the actual work of cleaning the blood.
What your kidneys do
Filtering waste is just one of several jobs the kidneys handle. They are quietly running half a dozen critical systems:
- Filter the blood. Approximately 50 gallons of blood pass through the kidneys every day, with waste products excreted as urine.
- Regulate blood pressure. The kidneys control fluid volume and produce hormones (renin) that influence blood pressure throughout the body.
- Balance electrolytes. Sodium, potassium, calcium, magnesium, and phosphate are kept in narrow ranges by kidney function.
- Activate vitamin D. The kidneys convert vitamin D into its active form, which keeps bones healthy.
- Stimulate red blood cell production. Through the hormone erythropoietin, the kidneys signal the bone marrow to produce red blood cells.
- Maintain acid-base balance. The kidneys excrete acid and produce bicarbonate to keep blood pH stable.
Why kidney disease is often silent
The kidneys have substantial reserve capacity. You can lose up to 75% of kidney function before symptoms emerge. By the time fatigue, swelling, or changes in urination appear, the disease is often advanced. This is why blood and urine screening is recommended for anyone with diabetes, high blood pressure, family history of kidney disease, or age over 60.
How kidney function is measured
Two main tests give your nephrologist a clear picture of how well your kidneys are working:
- Estimated Glomerular Filtration Rate (eGFR): calculated from serum creatinine. A normal eGFR is 90 or higher. An eGFR below 60 for three months indicates chronic kidney disease.
- Urine Albumin-to-Creatinine Ratio (UACR): a urine test that detects early kidney damage. Above 30 mg/g indicates abnormal protein leakage — often the earliest sign of trouble.
Protecting kidney function
Once kidney tissue is damaged, it does not regenerate. The goal of nephrology care is slowing progression and preventing complications:
- Tight blood pressure control (target below 130/80 in most patients)
- Tight blood sugar control if you have diabetes
- Avoiding NSAIDs and other medications that can hurt the kidneys
- Treating risk factors like sleep apnea and obesity
- Adequate hydration without overload
If you have any of the risk factors above, ask your primary care doctor for a basic kidney panel. Early detection is everything in kidney disease.