What Is Chronic Kidney Disease (CKD)?
Definition: Chronic kidney disease (CKD) is the presence of kidney damage or decreased kidney function for > 3 months. (<3 months is considered acute kidney disease.)
Nephron: each individual functional unit of the kidney, consisting of a glomerulus (the renal corpuscle–a tuft of capillaries) and its associated tubule.
Glomerular Filtration Rate (GFR): Kidney function is determined by glomerular filtration rate, which is a sum of the function of all working nephrons. The fewer the number of functioning nephrons, the lower the GFR and the more disease is present. GFR is merely a gauge to classify degrees of kidney dysfunction:
- Normal GFR is 125 mL/min/1.73 m2 (filtered blood per minute as applied to body size/area)
- Chronic kidney disease is a GFR < 60 (mL/min/1.73 m2)
- Kidney failure is a GFR or < 15 (mL/min/1.73 m2)
Kidney damage refers to structural or functional abnormalities other than a decreased GFR, such as
- Glomerular disease from diabetes, autoimmune disease, infection, drug toxicity, or malignancy
- Vascular disease (affecting blood supply to the kidneys) from atherosclerosis, hypertension, ischemia, or vasculitis
- Tubular disease (kidney tubules disease), from infections, stones, obstruction, or drug toxicity
- Congenital abnormality of the anatomy (e.g., polycystic kidney disease)
Signs and Symptoms of CKD
- Edema (swelling)
- Decreased urine output (“oliguria”)
The body’s biochemical reactions all work best at an ideal pH (measurement of acidity/alkalinity due to urinary excretion of the daily acids accrued through normal metabolism). When the kidney falters in this task, the acids are not eliminated efficiently and the blood becomes more acid (acidotic, or a lowering of pH). Compensatory mechanisms (excretion of ammonium) fail when GFR falls below 40-50 mL/minute. Chronic acidosis from chronic kidney disease results in bone resorption (osteopenia), muscle protein breakdown, hyperparathyroidism, impaired cardiac muscle/heart failure, insulin resistance (diabetes), and hypotension.
Clinical Course of CKD
With progressive failure, the dysfunction in CKD and its acidosis can eventually reach a point at which either physiological or medical compensation is no longer enough to be compatible with life, and at this point–called “end-stage renal failure”(ESRF)–either dialysis or kidney transplant is necessary.
How Is Chronic Kidney Disease Diagnosed?
U/A: The initial test in evaluating the kidney is the urinalysis (U/A). It can assess
- Turbidity: Cloudiness, indicating particulate matter, such as white blood cells (pus), red blood cells, epithelial cells, uric acid and other crystals, sediment, tubular casts (tubule-shaped clumps of white blood cells or red blood cells), and bacteria;
- Color: Dark due to dehydration or because of myoglobin (filtered debris of muscle damage); red or brown urine (tinged with blood); and
- Biochemical markers via dipstick: A mini-battery of tests for the presence of glucose, blood, nitrite, protein, pH, and specific gravity (how much the weight differs from plain water).
Microscopic evaluation is done with a spun-down urine to examine the sediment:
- Crystals: Uric acid (suggestive of acute kidney injury/tumor), calcium, cystine, and magnesium ammonium phosphate (consistent with infection)
- Microorganisms: Bacteria, fungi
- Cells: red blood cells (hematuria), white blood cells (pyuria), and epithelial or tumor cells
Red blood cells (RBCs) are normally absent in the urine, but when present can represent benign temporary effects from exercise, sexual intercourse, or menstrual contamination; alternately, hematuria could be the first evidence of malignancy, especially in the elderly. Red blood cells are also associated with intrinsic kidney disease, such as glomerulonephritis (inflammation of the nephron), or systemic disease, such as sickle cell anemia or systemic anemia from hemolysis (RBC destruction). The mechanical shearing of delicate urinary tract tissue from stone migration can cause microscopic hematuria.
White blood cells (WBCs) should not be present and when present indicate infection until ruled out (via a urine culture). In non-infectious pyuria (“sterile pyuria”), kidney stones or intrinsic kidney disease (e.g., nephritis) is considered.
- Casts: Cylinders of compressed structures that have loosened from the tubules and passed intact into the urine. When they are primarily made of protein, urinary acidity (low pH) or high urine concentration causes them.
RBC casts indicate intrinsic disease in the kidney, such as glomerulonephritis.
WBC casts indicate inflammation and infection, such as pyelonephritis infection.
GFR: Glomerular filtration rate is used to classify kidney damage and dysfunction, assessed as filtered blood per minute as applied to body size/area, i.e, mL/min/1.73 m2.
- Normal GFR is 125
- Chronic kidney disease is a GFR < 60
- Kidney failure is a GFR or < 15
Proteinuria/Albuminuria: chronic kidney disease (CKD) can be described in terms of abnormal amounts of protein spilled into the urine from filtration abnormalities; normal filtration is designed to keep albumin in the blood by way of limiting its excretion via glomerular permeability. When the permeability is abnormal, too much is excreted, and this can be determined by urinalysis.
Serum creatinine: elevated in those with CKD, even when they have no symptoms that would otherwise provoke suspicion. For this reason, the creatinine level is included in the routine metabolic profile blood test, which along with a complete blood count (CBC), is the universal starting point of screening in primary care. An albumin/creatinine ratio allows meaningful integration of these two components that increases accuracy of determining the degree of kidney dysfunction.
- Ultrasound can reveal small-sized kidneys, indicative of long-term scarring from infection. Structural anatomy, as is abnormal in congenital polycystic kidney disease, congenital absence of a kidney, or misplacement as a “pelvic” kidney can be identified.
- Kidney biopsy under ultrasound guidance: The position of the kidneys makes them very accessible to biopsy with just a needle insertion through the skin, visualized in real time with bedside ultrasound. A biopsy is done for an exact diagnosis, to judge the efficacy of treatment, to separate acute kidney disease or injury from chronic kidney disease, and to diagnose genetic disease.
- CT and MRI are also useful when other imaging is inconclusive.
- X-rays are all that are needed to identify a stone obstruction.
- Intravenous pyelogram: The injection of dye into the blood that is cleared through the urine, can light up the entire urinary tract to identify congenital anomalies, obstruction, or physical distortions to the kidneys, ureters, or bladder.
Management of Chronic Kidney Disease
When filtration via the glomeruli and tubules (together, the “nephron” unit) declines with chronic kidney disease (CKD), the other nephrons compensate via “hyperfiltration.” While initially helpful, hyperfiltration ends up causing long-term damage and scarring in them, resulting in progressive kidney disease.
The gradual decline in kidney function in CKD is initially asymptomatic but is relentless toward end-stage renal disease (ESRD). Besides jeopardizing the kidney, it also increases the risk of cardiovascular disease from associated hypertension, diabetes, and a metabolic syndrome. Because of this, management and treatment of CKD is part of a combination management that includes heart health.
Management of CKD is focused on both treating symptoms and complications and on delay in progression.
Treatment of reversible causes:
- Hypovolemia/decreased renal perfusion, from vomiting, diarrhea, hypotension, and diuretics.
- Elimination of nephrotoxic drugs (certain antibiotics, GI acid reducers, or antifungal agents).
- Urinary tract obstruction, addressed by dissolution, retrieval, or passage of a stone.
Treatment of reversible consequences:
- Acidosis can be mitigated by sodium bicarbonate therapy to prevent its consequences (CKD progression, bone deterioration, and malnutrition). Such “alkali” therapy slows progression of CKD
- Treatment for hypertension (in its vicious cycle with CKD) with antihypertensive medication, weight management, and smoking cessation
- Treatment of dyslipidemia (cholesterol/triglyceride elevations) with statin drugs
- Reduction of proteinuria/albuminuria (excreting protein/albumin in the urine), with ACE inhibitors or angiotensin receptor blockers; protein restriction
- Glycemic control and maintenance of a target hemoglobin A1c level, which can slow albuminuria
Treatment of complications of CKD:
- Electrolyte imbalance (potassium, calcium, phosphate, sodium, etc.)
- Anemia from iron, vitamin B12, or folate deficiency
- Dyslipidemia (abnormal lipid–cholesterol/triglycerides)
- Pericarditis and pericardial effusions
- Neuropathy (cognitive changes related to uremia)
- Hypothyroidism from impaired excretion of thyroid hormones
- Prevention of infection (immunizations), as the general debilitation from CKD makes one prone to communicable diseases
End-Stage Renal Failure (ESRF)
With progressive failure, the dysfunction in CKD can eventually reach “end-stage renal failure” (ESRF), treated with either dialysis or kidney transplant, or dialysis while awaiting kidney transplant.
How Can I Prevent Chronic Kidney Disease?
To reduce the risk of developing chronic kidney disease:
- Follow instructions on over-the-counter medications. When using nonprescription pain relievers, such as aspirin, ibuprofen (Advil, Motrin IB, others) and acetaminophen (Tylenol, others), follow the instructions on the package. Taking too many pain relievers could lead to kidney damage and generally should be avoided if you have kidney disease. Ask your doctor whether these drugs are safe for you.
- Maintain a healthy weight. If you’re at a healthy weight, work to maintain it by being physically active most days of the week. If you need to lose weight, talk with your doctor about strategies for healthy weight loss. Often this involves increasing daily physical activity and reducing calories.
- Don’t smoke. Cigarette smoking can damage your kidneys and make existing kidney damage worse. If you’re a smoker, talk to your doctor about strategies for quitting smoking. Support groups, counseling and medications can all help you to stop.
- Manage your medical conditions with your doctor’s help. If you have diseases or conditions that increase your risk of kidney disease, work with your doctor to control them. Ask your doctor about tests to look for signs of kidney damage.