Kidney disease can be caused by acute (i.e., bacterial infection, obstruction in the urinary tract, or damage to the renal parenchyma) or chronic conditions. Chronic kidney disease (CKD) is emphasized in this chapter because patients with CKD are more likely to present for dental care than those with acute disease.
Chronic kidney disease is a worldwide problem that continues to increase in prevalence. CKD is associated with many serious medical problems; thus, dentists need to recognize the clinical status of these patients and must be cognizant of the possible adverse outcomes, as well as the principles of proper management. Progressive kidney disease can result in reduced renal function and ultimate kidney failure with effects on multiple organ systems. Potential manifestations include anemia, abnormal bleeding, electrolyte and fluid imbalance, hypertension, drug intolerance, and skeletal abnormalities that can affect the delivery of dental care. In addition, patients who have severe and progressive disease may require artificial filtration of the blood through dialysis or kidney transplantation (see Chapter 21 ). This chapter reviews the current knowledge on CKD and presents principles for dental management.
The kidneys have several important functions: They regulate fluid volume, filter waste and toxins, maintain acid–base balance of plasma; synthesize and release hormones (erythropoietin, 1,25-dihydroxycholecalciferol, and renin); are responsible for drug metabolism; and serve as the target organ for parathormone and aldosterone. Under normal physiologic conditions, 25% of the circulating blood perfuses the kidney each minute. The blood is filtered through a complex series of tubules and glomerular capillaries within the nephron, the functional unit of the kidney ( Fig. 12.1 ). Ultrafiltrate, the precursor of urine, is produced in nephrons at a rate of about 125 mL/min/1.73 m 2 .
Chronic kidney disease is defined as abnormalities of kidney structure or function, present for 3 months or longer, with implications for health. It results from direct damage to nephrons or from progressive, chronic bilateral deterioration of nephrons. In CKD, the kidney damage is rarely repaired; thus, progressive disease (i.e., uremia and kidney failure) can lead to death. The rate of destruction and severity of disease depend on the underlying causative disorders and contributing factors, with diabetes and hypertension recognized as the primary etiologies.
The National Kidney Foundation defines a five-stage classification system for CKD ( Table 12.1 ) based on the glomerular filtration rate (GFR). Stage 1 is characterized by normal or only slightly increased GFR associated with some degree of kidney damage. This stage usually is asymptomatic, with a slight (10%–20%) decline in renal function. Stage 2 is marked by a mildly decreased GFR. Stage 3 is evidenced as a moderately decreased GFR (30–59 mL/min), with loss of 50% or more of normal renal function. Upon arriving at stage 3, persons are at higher risk for progressive CKD. Stage 4 is defined by a severely decreased GFR (15–29 mL/min). Stage 5 is reflected by renal failure, wherein 75% or more of the approximately 2 million nephrons have lost function (GFR <15 mL/min). With disease progression (stages 2–5), nitrogen products accumulate in the blood, and the kidneys perform fewer excretory, endocrine, and metabolic functions, with eventual loss of the ability to maintain normal homeostasis. The resultant clinical syndrome—caused by renal failure, retention of excretory products, and interference with endocrine and metabolic functions—is called uremia.