Chronic Kidney Disease - Chronic Kidney Disease Stages

Chronic kidney disease (CKD), also known as chronic renal disease, is progressive loss in kidney function over a period of months or years. The symptoms of worsening kidney function are not specific, and might include feeling generally unwell and experiencing a reduced appetite. Often, chronic kidney disease is diagnosed as a result of screening of people known to be at risk of kidney problems, such as those with high blood pressure or diabetes and those with a bloodline relative with CKD. This disease may also be identified when it leads to one of its recognized complications, such as cardiovascular disease, anemia, pericarditis or renal osteodystrophy (the lat ter included in the novel term CKD-MBD). CKD is a long-term form of kidney disease; thus, it is differentiated from acute kidney disease (acute kidney injury) in that the reduction in kidney function must be present for over 3 months. CKD is an internationally recognized public health problem affecting 5â€"10% of the world population.

Chronic kidney disease is identified by a blood test for creatinine, which is a breakdown product of muscle metabolism. Higher levels of creatinine indicate a lower glomerular filtration rate and as a result a decreased capability of the kidneys to excrete waste products. Creatinine levels may be normal in the early stages of CKD, and the condition is discovered if urinalysis (testing of a urine sample) shows the kidney is allowing the loss of protein or red blood cells into the urine. To fully investigate the underlying cause of kidney damage, various forms of medical imaging, blood tests, and sometimes a kidney biopsy (removing a small sample of kidney tissue) are employed to find out if a reversible cause for the kidney malfunction is present.

Previous professional guidelines classified the severity of CKD in five stages, with stage 1 being the mildest and usually causing few symptoms and stage 5 being a severe illness with poor life expectancy if untreated. Stage 5 CKD is often called end-stage kidney disease, end-stage renal disease, or end-stage kidney failure, and is largely synonymous with the now outdated terms chronic renal failure or chronic kidney failure; and usually means the patient requires renal replacement therapy, which may involve a form of dialysis, but ideally constitutes a kidney transplant. Recent international guidelines reclassified CKD based on cause, glomerular filtration rate category (G1,G2,G3a,G3b,G4 and G5), and albuminuria category (A1,A2,A3).

Screening of at-risk people is important because treatments exist that delay the progression of CKD. If an underlying cause of CKD, such as vasculitis, or obstructive nephropathy (blockage to the drainage system of the kidneys) is found, it may be treated directly to slow the damage. In more advanced stages, treatments may be required for anemia and kidney bone disease [also called renal osteodystrophy, secondary hyperparathyroidism or chronic kidney disease â€" mineral bone disorder (CKD-MBD)]. Chronic kidney disease was the cause of 956,000 deaths globally in 2013, up from 409,000 in 1990.

Signs and symptoms

CKD is initially without specific symptoms and is generally only detected as an increase in serum creatinine or protein in the urine. As the kidney function decreases:

• Blood pressure is increased due to fluid overload and production of vasoactive hormones created by the kidney via the renin-angiotensin system, increasing one's risk of developing hypertension and/or suffering from congestive heart failure.
• Urea accumulates, leading to azotemia and ultimately uremia (symptoms ranging from lethargy to pericarditis and encephalopathy). Due to its high systemic circulation, urea is excreted in eccrine sweat at high concentrations and crystallizes on skin as the sweat evaporates ("uremic frost").
• Potassium accumulates in the blood (hyperkalemia with a range of symptoms including malaise and potentially fatal cardiac arrhythmias). Hyperkalemia usually does not develop until the glomerular filtration rate falls to less than 20-25 ml/min/1.73 m², at which point the kidneys have decreased ability to excrete potassium. Hyperkalemia in CKD can be exacerbated by acidemia (which leads to extracellular shift of potassium) and from lack of insulin.
• Erythropoietin synthesis is decreased causing anemia.
• Fluid volume overload symptoms may range from mild edema to life-threatening pulmonary edema.
• Hyperphosphatemia, due to reduced phosphate excretion, follows the decrease in glomerular filtration. Hyperphosphatemia is associated with increased cardiovascular risk, being a direct stimulus to vascular calcification. Moreover, circulating concentrations of fibroblast growth factor-23 (FGF-23) increase progressively as the renal capacity for phosphate excretion declines, but this adaptative response may also contribute to left ventricular hypertrophy and increased mortality in CKD patients.
• Hypocalcemia, due to 1,25 dihydroxyvitamin D₃ deficiency (caused by stimulation of FGF-23 and reduction of renal mass), and resistance to the calcemic action of parathyroid hormone. Osteocytes are responsible for the increased production of FGF-23, which is a potent inhibitor of the enzyme 1-alpha-hydroxylase (responsible for the conversion of 25-hydroxycholecalciferol into 1,25 dihydroxyvitamin D₃). Later, this progresses to secondary hyperparathyroidism, renal osteodystrophy, and vascular calcification that further impairs cardiac function. An extreme consequence is the occurrence of the rare condition named calciphylaxis.

• The concept of chronic kidney disease-mineral bone disorder (CKD-MBD) currently describes a broader clinical syndrome that develops as a systemic disorder of mineral and bone metabolism due to CKD manifested by either one or a combination of: 1) abnormalities of calcium, phosphorus (phosphate), parathyroid hormone, or vitamin D metabolism; 2) abnormalities in bone turnover, mineralization, volume, linear growth, or strength (renal osteodystrophy); and 3) vascular or other soft-tissue calcification. CKD-MBD has been associated to poor hard outcomes.
• Metabolic acidosis (due to accumulation of sulfates, phosphates, uric acid etc.) may cause altered enzyme activity by excess acid acting on enzymes; and also increased excitability of cardiac and neuronal membranes by the promotion of hyperkalemia due to excess acid (acidemia). Acidosis is also due to decreased capacity to generate enough ammonia from the cells of the proximal tubule.
• Iron deficiency anemia, which increases in prevalence as kidney function decreases, is especially prevalent in those requiring haemodialysis. It is multifactoral in cause, but includes increased inflammation, reduction in erythropoietin, and hyperuricemia leading to bone marrow suppression.

People with CKD suffer from accelerated atherosclerosis and are more likely to develop cardiovascular disease than the general population. Patients afflicted with CKD and cardiovascular disease tend to have significantly worse prognoses than those suffering only from the latter.

Sexual dysfunction is very common in both men and women with CKD. A majority of men have a reduced sex drive, difficulty obtaining an erection, and reaching orgasm, and the problems get worse with age. A majority of women have trouble with sexual arousal, and painful menstruation and problems with performing and enjoying sex are common.

Causes

The most common recognised cause of CKD is diabetes mellitus. Others include idiopathic (i.e. unknown cause, often associated with small kidneys on renal ultrasound), hypertension, and glomerulonephritis. Together, these cause about 75% of all adult cases.

Historically, kidney disease has been classified according to the part of the kidney anatomy involved.

• Vascular disease includes large vessel disease such as bilateral renal artery stenosis and small vessel disease such as ischemic nephropathy, hemolytic-uremic syndrome, and vasculitis.
• Glomerular disease comprises a diverse group and is classified into:
  • Primary glomerular disease such as focal segmental glomerulosclerosis and IgA nephropathy (or nephritis)
  • Secondary glomerular disease such as diabetic nephropathy and lupus nephritis
• Congenital disease such as polycystic kidney disease.
• Tubulointerstitial disease includes drug- and toxin-induced chronic tubulointerstitial nephritis, and reflux nephropathy.
• Obstructive nephropathy is exemplified by bilateral kidney stones and diseases of the prostate.
• On rare cases, pinworms infecting the kidney can also cause nephropathy.
• Nontraditional causes of CKD (CKDu) are denoted if the common causes of CKD are not present:
  • CKD of unknown etiology is the subject of a major study by the Sri Lanka Ministry of Health and the World Health Organization 2009â€"2012.
  • Mesoamerican nephropathy, a form of CKDu, is "a new form of kidney disease that could be called agricultural nephropathy".

Diagnosis

Diagnosis of CKD is largely based on the clinical picture combined with the measurement of the serum creatinine level (see above).

Etiology

In many CKD patients, previous kidney disease or other underlying diseases are already known. A significant number present with CKD of unknown cause. In these patients, a cause is occasionally identified retrospectively.

Differential diagnosis

It is important to differentiate CKD from acute kidney injury (AKI) because AKI can be reversible. Abdominal ultrasound, in which the size of the kidneys is measured, is commonly performed. Kidneys with CKD are usually smaller (≤ 9 cm) than normal kidneys, with notable exceptions such as in early diabetic nephropathy and polycystic kidney disease. Another diagnostic clue that helps differentiate CKD from AKI is a gradual rise in serum creatinine (over several months or years) as opposed to a sudden increase in the serum creatinine (several days to weeks). If these levels are unavailable (because the patient has been well and has had no blood tests), it is occasionally necessary to treat a patient briefly as having AKI until the kidney impairment has been established to be irreversible.

Work-up

Additional tests may include nuclear medicine MAG3 scan to confirm blood flow and establish the differential function between the two kidneys. Dimercaptosuccinic acid (DMSA) scans are also used in kidney imaging; with both MAG3 and DMSA being used chelated with the radioactive element technetium-99.

Toxins

In CKD numerous uremic toxins accumulate in the blood. Even when ESKD (largely synonymous with CKD5) is treated with dialysis, the toxin levels do not go back to normal as dialysis is not that efficient. Similarly, after a kidney transplant, the levels may not go back to normal as the transplanted kidney may not work 100%. If it does, the creatinine level is often normal. The toxins show various cytotoxic activities in the serum and have different molecular weights, and some of them are bound to other proteins, primarily to albumin. Such toxic protein-bound substances are receiving the attention of scientists who are interested in improving the standard chronic dialysis procedures used today.

Screening

Screening those who have neither symptoms nor risk factors for CKD is not recommended. Those who should be screened include: those with hypertension or history of cardiovascular disease, those with diabetes or marked obesity, those aged > 60 years, subjects with indigenous racial origin, those with a history of kidney disease in the past and subjects who have relatives who had kidney disease requiring dialysis. Screening should include calculation of estimated GFR from the serum creatinine level, and measurement of urine albumin-to-creatinine ratio (ACR) in a first-morning urine specimen (this reflects the amount of a protein called albumin in the urine), as well as a urine dipstick screen for hematuria. The GFR (glomerular filtration rate) is derived from the serum creatinine and is proportional to 1/creatinine, i.e. it is a reciprocal relationship (the higher the creatinine, the lower the GFR). It reflects one aspect of kidney function: how efficiently the glomeruli (filterin g units) work. But as they make up <5% of the mass of the kidney, the GFR does not tell you about all aspects of kidney health and function. This can be done by combining the GFR level with the clinical assessment of the patient (especially fluid state) and measuring the levels of hemoglobin, potassium, phosphate and parathyroid hormone (PTH). Normal GFR is 90-120 mLs/min. The units of creatinine vary from country to country.

Referral to nephrologist

Guidelines for referral to a nephrologist vary between countries. Though most would agree that nephrology referral is required by Stage 4 CKD (when eGFR/1.73m² is less than 30 ml/min; or decreasing by more than 3 ml/min/year); and may be useful at an earlier stage (e.g. CKD3) when urine albumin-to-creatinine ratio is more than 30 mg/mmol, when blood pressure is difficult to control, or when hematuria or other findings suggest either a primarily glomerular disorder or secondary disease amenable to specific treatment. Other benefits of early nephrology referral include proper patient education regarding options for renal replacement therapy as well as pre-emptive transplantation, and timely workup and placement of an arteriovenous fistula in those patients opting for future hemodialysis

Severity-based stages

All individuals with a glomerular filtration rate (GFR) <60 ml/min/1.73 m² for 3 months are classified as having chronic kidney disease, irrespective of the presence or absence of kidney damage. The rationale for including these individuals is that reduction in kidney function to this level or lower represents loss of half or more of the adult level of normal kidney function, which may be associated with a number of complications such as the development of cardiovascular disease.

Protein in the urine is regarded as an independent marker for worsening of kidney function and cardiovascular disease. Hence, British guidelines append the letter "P" to the stage of chronic kidney disease if protein loss is significant.

Stage 1 Slightly diminished function; kidney damage with normal or relatively high GFR (≥90 ml/min/1.73 m²). Kidney damage is defined as pathological abnormalities or markers of damage, including abnormalities in blood or urine tests or imaging studies.

Stage 2 Mild reduction in GFR (60â€"89 ml/min/1.73 m²) with kidney damage. Kidney damage is defined as pathological abnormalities or markers of damage, including abnormalities in blood or urine tests or imaging studies.

Stage 3 Moderate reduction in GFR (30â€"59 ml/min/1.73 m²):. British guidelines distinguish between stage 3A (GFR 45â€"59) and stage 3B (GFR 30â€"44) for purposes of screening and referral.

Stage 4 Severe reduction in GFR (15â€"29 ml/min/1.73 m²) Preparation for renal replacement therapy.

Stage 5 Established kidney failure (GFR <15 ml/min/1.73 m²), permanent renal replacement therapy, or end-stage kidney disease.

NDD-CKD vs. ESRD

The term "non-dialysis-dependent chronic kidney disease" (NDD-CKD) is a designation used to encompass the status of those persons with an established CKD who do not yet require the life-supporting treatments for kidney failure known as renal replacement therapy (RRT, including maintenance dialysis or kidney transplantation). The condition of individuals with CKD, who require either of the two types of renal replacement therapy (dialysis or transplant), is referred to as the end-stage kidney disease (ESKD). Hence, the start of the ESKD is practically the irreversible conclusion of the NDD-CKD. Even though the NDD-CKD status refers to the status of persons with earlier stages of CKD (stages 1 to 4), patients with advanced stage of CKD (stage 5), who have not yet started renal replacement therapy, are also referred to as NDD-CKD.

Treatment

The presence of CKD confers a markedly increased risk of cardiovascular disease, and people with CKD often have other risk factors for heart disease, such as high blood lipids. The most common cause of death in people with CKD is cardiovascular disease rather than kidney failure. Aggressive treatment of hyperlipidemia is warranted.

Apart from controlling other risk factors, the goal of therapy is to slow down or halt the progression of CKD to stage 5. Control of blood pressure and treatment of the original disease, whenever feasible, are the broad principles of management. Generally, angiotensin converting enzyme inhibitors (ACEIs) or angiotensin II receptor antagonists (ARBs) are used, as they have been found to slow the progression of CKD to kidney failure. They have also been found to reduce the risk of major cardiovascular events such as myocardial infarction, stroke, heart failure, and death from cardiovascular disease when compared to placebo in individuals with CKD. Furthermore, ACEIs may be superior to ARBs for protection against progression to kidney failure and death from any cause in those with CKD.

Although the use of ACE inhibitors and ARBs represents the current standard of care for people with CKD, people progressively lose kidney function while on these medications, as seen in the IDNT and RENAL studies, which reported a decrease over time in estimated GFR (an accurate measure of CKD progression, as detailed in the K/DOQI guidelines) in people treated by these conventional methods.

Replacement of erythropoietin and calcitriol, two hormones processed by the kidney, is often necessary in people with advanced disease. Guidelines recommend treatment with parenteral iron prior to treatment with erythropoietin. A target hemoglobin level of 9â€"12 g/dl is recommended. The normalization of hemoglobin has not been found to be of benefit. It is unclear if androgens help with anemia. Phosphate binders are also used to control the serum phosphate levels, which are usually elevated in advanced chronic kidney disease. Although the evidence for them is limited, phosphodiesterase-5 inhibitors and zinc show potential for helping men with sexual dysfunction.

At stage 5 CKD, renal replacement therapy is usually required, in the form of either dialysis or a transplant.

Prognosis

The prognosis of patients with chronic kidney disease is guarded as epidemiological data have shown that all cause mortality (the overall death rate) increases as kidney function decreases. The leading cause of death in patients with chronic kidney disease is cardiovascular disease, regardless of whether there is progression to stage 5.

While renal replacement therapies can maintain patients indefinitely and prolong life, the quality of life is severely affected. Kidney transplantation increases the survival of patients with stage 5 CKD significantly when compared to other therapeutic options; however, it is associated with an increased short-term mortality due to complications of the surgery. Transplantation aside, high-intensity home hemodialysis appears to be associated with improved survival and a greater quality of life, when compared to the conventional three-times-a-week hemodialysis and peritoneal dialysis.

Cancer risk

Patients with ESKD are at increased overall risk for cancer. This risk is particularly high in younger patients and gradually diminishes with age. Medical specialty professional organizations recommend that physicians do not perform routine cancer screening in patients with limited life expectancies due to ESKD because evidence does not show that such tests lead to improved patient outcomes.

Epidemiology and prevalence

About one in ten people suffer from chronic kidney disease. African Americans, American Indians, Hispanics, and South Asians, particularly those from Pakistan, Sri Lanka, Bangladesh, and India, are at high risk of developing CKD. African Americans are at greater risk due to a prevalence of hypertension among them. As an example, 37% of ESKD cases in African Americans can be attributed to high blood pressure, compared with 19% among Caucasians.

People with high blood pressure and diabetes are also at high risk of suffering from CKD than those people without these underlying conditions. About one of five adults with hypertension and one of three adults with diabetes have CKD. Other health conditions that may lead to CKD are obesity, high cholesterol, a family history of the disease, lupus, and other forms of cardiovascular diseases.

Chronic kidney disease was the cause of 956,000 deaths globally in 2013, up from 409,000 deaths in 1990. In Canada 1.9 to 2.3 million people were estimated to have CKD in 2008. The U.S. Centers for Disease Control and Prevention found that CKD affected an estimated 16.8% of U.S. adults aged 20 years and older in the period from 1999 to 2004. UK estimates suggested that in 2007 8.8% of the population of Great Britain and Northern Ireland had symptomatic CKD.

Treatment efficacy also differs between racial groups. Administration of antihypertensive drugs generally halts disease progression in white populations but has little effect in slowing kidney disease among blacks, and additional treatment such as bicarbonate therapy is often required. While lower socioeconomic status contributes to the prevalence of CKD, significant differences in CKD prevalence are still evident between African Americans and Whites when controlling for environmental factors.

Studies have shown a true association between history of chronic kidney disease in first- or second-degree relatives, and risk of disease. In addition, African Americans may have higher serum levels of human leukocyte antigens (HLA). High HLA concentrations can contribute to increased systemic inflammation, which indirectly may lead to heightened susceptibility for developing kidney disease. Lack of nocturnal reduction in blood pressure among groups of African Americans is also offered as an explanation, which lends further credence to a genetic etiology of CKD racial disparities.

A high and so-far unexplained incidence of CKD, referred to as the Mesoamerican nephropathy, has been noted among male workers in Central America, mainly in sugar cane fields in the lowlands of El Salvador and Nicaragua. Heat stress from long hours of piece-rate work at high average temperatures of about 36 °C (96 °F) is suspected, as are agricultural chemicals and other factors. In Sri Lanka, another epidemic of CKD of unknown etiology has become a serious public health concern.

Society and culture

In the USA, the National Kidney Foundation is a national organization representing patients and professionals who treat kidney diseases. The American Kidney Fund is a national nonprofit organization providing treatment-related financial assistance to one of every five dialysis patients each year. The Renal Support Network is a nonprofit, patient-focused, patient-run organization that provides nonmedical services to those affected by CKD. The American Association of Kidney Patients is a nonprofit, patient-centric group focused on improving the health and well-being of CKD and dialysis patients. The Renal Physicians Association is an association representing nephrology professionals.

In the United Kingdom, the UK National Kidney Federation and British Kidney Patient Association (BKPA) represents patients, and the Renal Association represents renal physicians and works closely with the National Service Framework for kidney disease.

Kidney Health Australia

serves that country.

The International Society of Nephrology is an international body representing specialists in kidney diseases.

Research

Currently, several compounds are in development for the treatment of CKD. These include the angiotensin receptor blocker (ARB) olmesartan medoxomil; and sulodexide, a mixture of low molecular weight heparin and dermatan sulfate.

References

External links

• National Kidney Foundation
• Dialysis Complications of Chronic Renal Failure at eMedicine
• The Kidney Foundation of Canada
• Chronic Renal Failure Information from Great Ormond Street Hospital