Decreased kidney function is a common medical condition. The causes of decreased kidney function fall into two categories, acute and chronic. A sudden decrease in kidney function, within hours to days, is called acute kidney injury or AKI. The causes of AKI can be broken down into prerenal, intrinsic and postrenal, depending on the source of the problem. Decreased kidney function present for at least 3 months is considered chronic. The term for this is chronic kidney disease, and it is the most common cause of decreased kidney function.
Chronic kidney disease results when the tissues of the kidneys have been damaged beyond repair. More than 10 percent of adults in the United States have chronic kidney disease, according to the Centers for Disease Control and Prevention. The most common causes of this type of kidney disease are diabetes and high blood pressure. AKI can lead to chronic kidney disease if the damage is ongoing or the initial injury was so severe that repair cannot take place. The biggest concern with chronic kidney disease is the progression to end-stage renal disease, or ESRD. With ESRD, the kidneys no longer function well enough to sustain life, and regular dialysis treatment is needed.
Prerenal Causes of AKI
The kidney tissues need oxygen, carried in the blood, to function normally. Prerenal causes of decreased kidney function result from decreased blood flow to the kidney. This is the most common cause of AKI. In most cases, the kidneys are normal. but the function is impaired due to reduced blood flow. A few examples of causes include:
-- Dehydration caused by diarrhea, vomiting or excessive sweating.
-- Lack of blood flow to the kidneys caused by a heart failure.
-- Medicines like ibuprofen (Advil, Motrin) and lisinopril (Prinivil, Zestril) that decrease blood flow to the kidneys.
-- Water pills, or diuretics, such as hydrochlorothiazide (Hydra-zide, Microzide) that can lead to dehydration.
-- Low blood pressure caused by loss of blood volume from bleeding.
Intrinsic Causes of AKI
Diseases that impact the structures within the kidney leading to decreased kidney function are referred to as intrinsic causes. In this case, the tissues within the kidneys are directly damaged. Examples of this type of kidney injury include:
-- Prolonged dehydration leading to death of kidney cells called acute tubular necrosis.
-- Medications such as the antibiotic amoxicillin (Amoxil, Moxatag) and the acid reducer omeprazole (Prilosec, Prilosec OTC) that can lead to direct destruction of kidney cells called acute interstitial nephritis.
-- Small blood clots or clots of cholesterol that get stuck in the small blood vessels of the kidney.
-- Goodpasture syndrome and systemic lupus erythematosus that damage the kidneys when the immune system mistakenly attacks proteins within the kidneys.
Postrenal Causes of AKI
Postrenal AKI occurs when urine flow is blocked. The urine leaves each kidney through a tube called a ureter. The ureters direct urine to the bladder. As with prerenal disease, the kidneys may be normal but sustain damage due to the pressure backup as urine is not flowing out. As the collecting system of the kidneys enlarges to accommodate the urine backup, other kidney tissues are compressed and damaged. Assuming two normal kidneys, the blockage must impact both kidneys to impact kidney function. Examples of this kind of kidney damage include:
-- Enlarged prostate.
-- A tumor in the bladder.
-- Blood clots filling the bladder.
If one kidney is absent or already impaired, blockage of the healthy kidney can lead to an overall decrease in kidney function. In addition to the causes already mentioned, a kidney stone can block the tube of the functioning kidney and result in decreased function.
Warnings and Precautions
Appropriately functioning kidneys are essential for good health. Signs of worsening kidney function can be subtle, but if you experience a decrease in urination or your urine is dark or bright red, call your doctor. If you have any concerns about how your kidneys are functioning or how your medications may impact your kidneys, do not hesitate to contact your doctor. If you have chronic kidney disease, talk with your doctor about your prescription and over-the-counter medications. Seek immediate medical care if you have not urinated for 24 hours.