A Simple Guide to Urinary Excretion and Kidney Function (A Simple Guide to Medical Conditions)
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Based on information from references 3 and 12 through Proteinuria is associated with more rapid progression of chronic kidney disease and a greater likelihood of developing end-stage renal disease.
Consequently, detection and quantitation of proteinuria are essential to the diagnosis and treatment of chronic kidney disease. Reducing proteinuria with an angiotensin-converting enzyme ACE inhibitor or an angiotensin-II receptor blocker ARB slows the progression of chronic kidney disease in patients with or without diabetes.
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Albumin, the predominant protein excreted by the kidney in most types of renal disease, is detected readily by urine dip-stick testing. In some conditions, immunoglobulins also may be excreted in urine.
Chronic Kidney Disease
The protein-creatinine ratio in an early-morning random urine sample correlates well with hour urine protein excretion and is much easier to obtain. Albuminuria was detected in one of every three persons with diabetes, one of every seven persons with hypertension but no diabetes, and one of every six persons older than 60 years.
Microalbuminuria often heralds the onset of diabetic nephropathy. In a recent study 21 of patients with type 1 diabetes, spontaneous regression of microalbuminuria occurred in some patients, suggesting that microalbuminuria may represent an initial reversible phase of kidney damage rather than the beginning of an inexorable progression to end-stage renal disease.
Screening can be performed using a microalbumin-sensitive dipstick or analysis of a random morning urine sample to determine the microalbumin-creatinine ratio. Microalbumin dipsticks have a sensitivity of 51 to percent and a specificity of 27 to 97 percent. An algorithm for detecting proteinuria and microalbuminuria is provided in Figure 1. Algorithm for proteinuria and microalbuminuria screening in the patient with risk factors for chronic kidney disease. Accessed online February 21, , at: The value of screening for microalbuminuria has been questioned in patients who already are receiving ACE-inhibitor therapy 26 on the basis that the results are unlikely to change management.
One study 27 in patients with type 2 diabetes showed that increasing the dose of an ARB to decrease or eliminate microalbuminuria provides additional benefit in slowing progression to overt nephropathy. Therefore, current research suggests that it may be beneficial to monitor patients with chronic kidney disease, including those who are taking an ACE inhibitor or ARB, for persistence of microalbuminuria or for progression to overt proteinuria. The medication dosage should be adjusted as tolerated, with the goal of eliminating albuminuria.
Once chronic kidney disease has been identified, goals include determining the stage of the disease, establishing the cause of the disease, and evaluating comorbid conditions. All patients with chronic kidney disease should undergo urinalysis and renal imaging as part of the diagnostic evaluation. Patients with long-standing diabetes, hypertension, and a clinical course consistent with chronic kidney disease secondary to these conditions may not require further evaluation.
The evaluation of all patients is guided by the symptoms e. Underlying diseases may be identified by the physical examination, with special attention given to the skin, joints, and cardiovascular system. Table 5 28 summarizes the common presentations and appropriate serologic evaluations for the most common causes of chronic kidney disease. History and physical examination: Volume depletion, hypotension, congestive heart failure, cirrhosis, atherosclerosis. KUB radiography, intravenous pyelography, spiral CT scanning, renal ultrasonography. Pelvic examination, urine culture, voiding cystourethrography, renal ultrasonography, CT scanning.
Palpable kidneys with or without family history of cystic kidney disease, flank pain. Late-onset or refractory hypertension, sudden onset of hypertension in young woman, smoking history, abdominal bruit. Renal Doppler ultrasonography, radioisotope renal scanning, MRA, renal angiography. Management in the primary care setting. Accessed February 24, , at: Several tests may help determine the underlying cause of chronic kidney disease. Tests for complements 3 and 4 are used to screen for collagen vascular disease, hepatitis C—related disease, and infection-related immune complex disease.
The antineutrophil cytoplasmic antibody assay identifies vasculitis, whereas serum protein electrophoresis and urine protein electrophoresis detect multiple myeloma. Renal ultrasonography helps establish the diagnosis and prognosis by documenting the size of the kidneys.
Normal size indicates kidney disease that may be amenable to medical treatment. Small kidneys suggest irreversible disease. Asymmetry in kidney size suggests renovascular disease. Imaging studies that may be useful in identifying the cause of chronic kidney disease are listed in Table 6. Based on an international survey 29 of nephrologists, rates of biopsy vary widely in practice. Intravenous pyelography generally is not performed in patients with chronic kidney disease because it may precipitate acute renal failure. Information from references 1 and The management of chronic kidney disease depends on the specific treatment of the underlying cause, the stage of the kidney disease, and the presence or absence of proteinuria.
Treatment goals for all patients include slowing disease progression, detecting and managing complications, and preventing cardiovascular disease. The rate of progression for chronic kidney disease depends on the underlying cause. In general, tubulointerstitial diseases progress more slowly than do glomerular diseases, diabetic and hypertensive nephropathy, and polycystic kidney disease.
In rapidly progressing kidney disease, the GFR may decrease by as much as 10 to 20 mL per minute per 1. In more slowly progressing disease, the GFR may decrease by as little as 2 mL per minute per 1. Plotting the GFR against time is helpful in estimating the rate of disease progression and the time to kidney failure, and it helps predict the need for kidney replacement therapy Figure 2 1. Estimating the progression of chronic kidney disease. A plot of the glomerular filtration rate GFR over time can be used to predict the time to end-stage renal disease.
Detection and Evaluation of Chronic Kidney Disease
Three interventions have been proved to slow the progression of kidney disease: Complications of chronic kidney disease affect every organ system. Patients with a GFR below 60 mL per minute per 1. Red blood cell indexes, reticulocyte count, iron studies, fecal occult blood test. Hypoalbuminemia, decreased levels of immunoglobulins in patients with nephritic levels of proteinuria or signs of malnutrition. Clinical evaluation may detect gastrointestinal, neurologic, dermatologic, and musculoskeletal complications in the advanced stages of chronic kidney disease.
Gastrointestinal symptoms may herald the onset of uremia, indicating the need for kidney replacement therapy. Laboratory tests detect complications such as electrolyte abnormalities, disordered calcium or phosphorus metabolism, and anemia. Patients with nephrotic-range proteinuria are at risk for hypoalbuminemia and immune dysfunction because of the loss of immunoglobulins.
Periodic monitoring of the total serum protein level and the albumin level is indicated in these patients. Nutritional status should be evaluated because malnutrition adversely affects prognosis. Cardiovascular disease is the most common cause of death in patients with chronic kidney disease. The risk of cardiovascular disease and associated mortality increases in proportion to the decrease in the GFR. Evaluation for traditional cardiovascular risk factors, including smoking, high lipid levels, hypertension, and sedentary lifestyle, is essential.
A long-term follow-up study 35 of patients with nondiabetic kidney disease and an average GFR of 32 mL per minute per 1. The KDOQI guidelines on managing dyslipidemias 36 in chronic kidney disease recommend a low-density lipoprotein cholesterol goal of less than mg per dL 2. In these patients, the year risk for mortality from cardiovascular disease exceeds 20 percent. Paradoxically, dialysis patients with the lowest cholesterol levels are the most likely to die of cardiovascular disease.
This is because low levels of cholesterol are associated with nontraditional cardiac risk factors of malnutrition and are markers of chronic inflammation. Additional cardiac risk factors specific to chronic kidney disease include volume overload, hyperparathyroidism, and uremia. Anemia caused by decreased erythropoietin production also may contribute to cardiovascular mortality.
Treatment with exogenous erythropoietin has been shown to improve the prognosis. Nephrology referral generally is recommended for patients with a serum creatinine level of 1. According to one estimate, that would mean seven new patients per day for every nephrologist in the United States. Information from references 6 , 11 , 28 , 38 , and The value of timely referral has been demonstrated, 40 but the contribution of primary care to outcomes in patients with chronic kidney disease has not been studied.
Already a member or subscriber? Snyder received her medical degree from the University of Vermont College of Medicine, Burlington, and completed a family medicine residency at San Francisco General Hospital. She completed a surgical internship, family medicine residency, faculty development fellowship, and sports medicine fellowship at Harbor-UCLA Medical Center.
The renal pelvis passes through it, as well as the:. The ureter is a tube of muscle that pushes urine into the bladder, where it collects and exits the body. Because of all of the vital functions the kidneys perform and the toxins they encounter, the kidneys are susceptible to various problems. Learn more about some of the most common kidney diseases. If you notice any of these symptoms, contact your doctor. Depending on your symptoms, they may do some kidney function tests to make a diagnosis. The kidneys are important organs that affect many other body parts, including the heart.
Follow these tips to keep them working efficiently:. Eating a lot of salty foods can disrupt the balance of minerals in the blood. This can make it harder for the kidneys to work properly. Try swapping out processed foods — which usually have a lot of added salt — for whole foods, such as:. High blood pressure is a known risk factor for chronic kidney disease. Regular exercise, even for just 20 minutes a day, can help reduce blood pressure. Drinking plenty of water helps the kidneys perform one of their most important functions: Learn more about how much water you should really be drinking every day.
Regularly taking certain over-the-counter medications, such as nonsteroidal anti-inflammatory drugs , can cause kidney damage over time. Occasionally taking them is fine, but work with your doctor to find alternatives if you have a condition that requires managing pain, such as arthritis. Several things can increase your risk of developing a kidney condition.
Make sure you regularly have your kidney function tested if you:. Learn fun facts about the digestive system you never knew. Did you know that most heart attacks happen on Monday?
Learn more fun facts about the heart. Signs and symptoms of kidney disease are often nonspecific, meaning they can also be caused by other illnesses. Because your kidneys are highly adaptable and able to compensate for lost function, signs and symptoms may not appear until irreversible damage has occurred. If you have a medical condition that increases your risk of kidney disease, your doctor is likely to monitor your blood pressure and kidney function with urine and blood tests during regular office visits. Ask your doctor whether these tests are necessary for you.
A normal kidney has about 1 million filtering units. Each unit, called a glomerulus, connects to a tubule, which collects urine. Conditions such as high blood pressure and diabetes take a toll on kidney function by damaging these filtering units and collecting tubules and causing scarring.
How do my kidneys work?
A healthy kidney left eliminates waste from the blood and maintains the body's normal chemical balance. Fluid-filled sacs right , called cysts, characterize polycystic kidney disease. Chronic kidney disease occurs when a disease or condition impairs kidney function, causing kidney damage to worsen over several months or years. Chronic kidney disease can affect almost every part of your body.
Potential complications may include:.
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This content does not have an English version. This content does not have an Arabic version. Overview Chronic kidney disease, also called chronic kidney failure, describes the gradual loss of kidney function. Request an Appointment at Mayo Clinic. Polycystic kidney A healthy kidney left eliminates waste from the blood and maintains the body's normal chemical balance. References Goldman L, et al.