Kidney and Genitourinary Disorders
General Renal Principles
Kidney function is indicated by the glomerular filtration rate (GFR).
The kidneys of children reach adult GFR at approximately 1 year of age, but measured GFR vary by age.
GFR can be estimated (eGFR) with the patient height, serum creatinine, and a constant (Schwartz equation). eGFR mL/minute/1.73 m2 = (k)(height)/serum creatinine
k = constant of 0.413 for all ages/genders.
Height is measured in centimeters.
Serum creatinine is measured in mg/dL.
Renal blood flow is dependent on intravascular volume and adequate cardiac output with oxygenated blood.
Fractional excretion of sodium.
Equation used to determine whether kidney dysfunction is only a result of hypoperfusion to kidney.
<1% prerenal (e.g., hypovolemia, sepsis, congestive heart failure).
>1% intrinsic (e.g., acute tubular necrosis, glomerulone-phritis [GN]).
>4% postrenal (e.g., obstruction, urolithiasis).
Normal ratio is 10:1 to 20:1.
Elevated ratios are often associated with shock or dehydration with acute kidney failure. Also may result from nephrolithiasis or gastrointestinal or pulmonary hemorrhage.
Low ratios are often associated with rhabdomyolysis, syndrome of inappropriate antidiuretic hormone secretion, lung disease, malignancy, low dietary protein intake, or certain medications.
Acute Renal Failure
Andrea M. Kline-Tilford
Also known as acute kidney failure.
An abrupt cessation or significant decline in the kidney’s ability to eliminate waste products, regulate acid-base balance, and regulate electrolyte balance.
Damage to renal epithelium results in secretion of vasoactive compounds (e.g., angiotensin, prostaglandins, nitric oxide, and endothelin).
Released vasoactive compounds result in increased vascular resistance and decreased blood flow, ultimately tubular damage. GFR is reduced and urine output decreases.
Many etiologies, including hemolytic uremic syndrome (HUS), shock, and GN.
Classified as prerenal, intrinsic renal, and postrenal.
Prerenal is the most common.
Highest mortality rates are associated with multiorgan system failure; however, complete recovery of kidney function occurs in some patients.
Medication history (e.g., nephrotoxic agents).
Vital signs (e.g., blood pressure, heart rate, temperature).
Fluid balance: urine output.
Serum electrolytes and complete blood count (CBC).
Consider hepatic panel if concern for hepatorenal syndrome.
Chest radiography if accompanied by respiratory symptoms.
Fluid management: judicious (e.g., restore intravascular volume or diuresis depending on clinical status). Aggressive hydration may result in fluid overload, pulmonary edema, and respiratory compromise.
Calculation of fractional excretion of sodium may help guide fluid management.
Fluid management with urine output replacement and calculated insensible losses may be warranted.
Box 16.1 Common Etiologies of Acute Renal Failure in Children
Prerenal Kidney Disease
Dehydration/depleted intravascular volume.
Distributive volume issues/decreased effective intravascular volume.
Intrinsic Kidney Disease
Acute tubular necrosis.
Ischemia/hypoxia in kidneys.
Infection (e.g., HUS, poststreptococcal GN).
Renal artery or vein thrombosis.
Endogenous toxins (e.g., myoglobin).
Exogenous toxins (e.g., methanol, ethylene glycol).
Bilateral ureteral obstruction.
Specific Genetic Conditions Associated with Acute Renal Failure
Polycystic kidney disease.
Nephrotic syndrome (focal segmental glomerulosclerosis, membranoproliferative GN).
Systemic lupus erythematosus (SLE).
Box 16.2 Presenting Signs and Symptoms of Acute Renal Failure
Shortness of breath.
Hyponatremia is common. Risk for seizure activity if serum sodium <125 mEq/L. Treat with hypertonic saline solution (e.g., 3% saline administration).
Hyperkalemia may be life-threatening (e.g., ventricular tachycardia, ventricular fibrillation).
EKG findings in hyperkalemia may include peaked T waves, prolongation of PR interval, widening of QRS complex, flattening of P waves.
Imperative to reduce extracellular potassium level and stabilize the cardiac cell membrane to avoid ventricular tachycardia/fibrillation. Glucose, sodium bicarbonate, insulin, and albuterol shift potassium into the cells.
Calcium chloride can stabilize the cardiac cell membrane.
Sodium polystyrene can exchange potassium and sodium in the colon.
Emergent dialysis is often indicated for serum potassium levels >7 mEq/L.
Hypertension therapy: avoid angiotensin-converting enzyme (ACE) inhibitors. Goal is normal blood pressure for gender and height.
Adjust medications that are renally excreted; consult a pharmacist.
Renal supportive therapies may be indicated. See more information on renal supportive therapies later in this section.
Urinary Tract Infection
Andrea M. Kline-Tilford
Bacterial or fungal infection in any part of the urinary tract (e.g., urethra, ureters, bladder, kidney).
Migration to the kidney results in pyelonephritis (e.g., upper urinary tract infection [UTI]).
Accounts for as many as 5% to 14% of all pediatric emergency department (ED) visits.
Common cause of hospitalization for infants and young children.
Uncircumcised males have the highest incidence in the first 3 months of life.
Genetic predisposition and history of dysfunctional voiding or elimination (e.g., encopresis) are associated with higher rates of UTI.
In otherwise healthy children, UTI may indicate an underlying abnormality in the urinary tract (e.g., vesicoureteral reflux (VUR) disease; varying degrees of severity).
Most common etiology is colonic organisms.
Commonly associated with gram-negative bacteria (e.g., Escherichia coli, Klebsiella species, and Pseudomonas aeruginosa), gram-positive bacteria (e.g., Enterococcus, Staphylococcus aureus, group B streptococcus).
Has also been associated with Candida, adenovirus, and herpes simplex virus.
Invasion of microorganisms (bacteria or fungi most commonly) into urethra, ascending the urinary tract to the bladder.
Pathogen infiltrates the mucosa of the bladder, resulting in an inflammatory response.
Infants/Young children: fever, irritability/fussiness, decreased appetite, lethargy or changes in activity level, jaundice, and/or weight loss.
Preschool/Young school age: abdominal pain, nausea/vomiting, and urinary frequency.
Older children: urinary frequency, dysuria, urgency, suprapubic pain, and/or nausea/vomiting.
Evaluate history for UTIs, structural abnormalities of the urinary tract, bubble baths, voiding/elimination dysfunction, sexual activity, maltreatment risk.
Physical examination: evaluate for sacral dimple, costovertebral angle, or suprapubic tenderness.
Urinalysis: presence of leukocyte esterase, nitrites, >5 white blood cells (WBCs), or bacteria/hpf.
Urine culture: identifies pathogen and evaluates antibiotic sensitivity/resistance.
More than 50,000 colony-forming units/mL of a single organism and pyuria represent UTI in appropriately obtained specimens.
Must consider collection method/route and clinical presentation.
Urinalysis and urine culture are recommended to determine the presence of a UTI.
Ultrasound: evaluates anatomy, kidney size/shape, and for evidence of hydronephrosis. Can also be used to evaluate for areas of inflammation and signs of pyelonephritis. Indications: UTI in children 2 months to 2 years of age.
Voiding cystourethrography: If renal and bladder ultrasound show hydronephrosis, scarring, or other evidence of high-grade VUR or obstructive uropathy, as well as in other atypical or complex clinical circumstances. Also indicated in all infants 2 months of age to 2 years with recurrence of febrile UTI.
Dimercaptosuccinic acid (DMSA) scintigraphy: Nuclear medicine scan used to evaluate for renal scarring.
Antibiotic therapy, tailored to specific organism when culture and sensitivities are available.
Duration of therapy determined by patient age, severity of illness, local resistance patterns, associated underlying disorders.
Uncomplicated UTI duration of therapy is 7 to 10 days; some studies support shorter duration of 2 to 4 days of therapy.
Complicated UTI therapy is generally 14 days.
Trimethoprim-sulfamethoxazole, amoxicillin-clavulanate, cefixime are acceptable selections for initial oral therapy.
Ceftriaxone, cefotaxime, gentamicin are acceptable selections for initial parenteral therapy.
In general, oral antibiotics are equally effective as parenteral therapy.
Hospitalization is recommended when children are unable to tolerate oral medications or maintain adequate hydration, failure to improve on outpatient therapy, evidence of sepsis/septic shock, or underlying medical conditions that may complicate the management of UTI.
Patient family education: signs of UTI, hygiene, limiting bubble baths, constipation prevention, urination after intercourse if sexually active.
Close clinical follow-up after 7 to 10 days of antimicrobial therapy to evaluate for recurrent UTI.
Underlying urinary tract abnormalities are important to recognize early so that they do not lead to renal scarring.
Prophylactic antibiotics do not reduce the risk of recurrent UTI, even in cases of mild-to-moderate VUR.
Bacterial infection of the upper urinary tract caused by an ascending infection originated in the lower urinary tract.
Most Common Etiologies
Gram-positive bacteria: Enterococcus spp. and Staph. aureus.
Gram-negative bacteria: E. coli, Klebsiella spp., Proteus spp., P. aeruginosa, Serratia spp., and Enterobacter aerogenes.
60% to 65% of children with febrile UTI also have acute pyelonephritis.
Most cases of acute pyelonephritis respond readily to antibiotics.
Bacterial invasion into the upper urinary tract with patchy interstitial inflammation and collections of neutrophils, leading to tubular necrosis.
Tachycardia, tachypnea, dehydration.
Pain (abdominal, suprapubic, flank, and/or costovertebral).
Urinalysis: rapid detection of leukocyte esterase and nitrites.
Urine culture with sensitivities: critical for determining organism and appropriate antibiotic therapy.
Basic metabolic panel: evaluation of kidney function.
CBC with differential: evaluation of WBC count and differential.
Blood culture: Positive culture indicates bacteremia.
C-reactive protein: elevated, indicating an inflammatory process.
Erythrocyte sedimentation rate: elevated, indicating an inflammatory process.
Renal ultrasound for children 2 to 24 months of age.
Intravenous (IV) antimicrobial therapy.
Voiding cystourethrography (VCUG): in some cases.
VCUG is typically reserved for children with recurrent febrile UTI who have evidence of abnormalities on ultrasound.
Inflammation within the kidney.
Primary (acute poststreptococcal GN, most common form) (see next section).
Deposits of immunoglobulins, complement, and cell-mediated immune reactions lead to inflammation and injury.
History of recent throat infection, decreased urine output, dark urine, fatigue, headache.
Rash on buttocks and posterior legs, arthralgia, and weight loss (symptoms of secondary GN).
Elevated blood pressure.
Other signs of fluid overload/congestive heart failure.
Electrolyte panel, creatinine, BUN, CBC with differential, urinalysis with urine culture and sensitivities, and throat culture.
If acute poststreptococcal GN is suspected, a serum antistreptolysin-O (ASO) titer should be checked.
To assess for systemic disease, autoimmune panels such as serum complement levels (C3, C4), lupus serologies, anti-DNase B, perinuclear antineutrophil antibody (P-ANCA), cellular antineutrophil cytoplasmic antibody (C-ANCA), and IgA are useful.
Low serum C3 levels are indicative of secondary GN.
Antibiotic: penicillin, first line.
Treatment of hypertension or acute renal insufficiency.
Judicious fluid management.
Calcium channel antagonists, vasodilators, or ACE inhibitors.
For secondary forms of GN.
Corticosteroids and cyclophosphamide to counteract the inflammatory process.
Acute Poststreptococcal Glomerulonephritis
Tamara L. Hill
Caused by a prior infection with specific nephritogenic strains of a beta-hemolytic streptococcus of the throat or skin.
Most common glomerular cause of hematuria.
Commonly follows group A streptococcal pharyngitis during the cold weather months and streptococcal skin infections or pyoderma during warm weather months.
Sudden onset of gross hematuria, edema, hypertension, and renal insufficiency.
Urinalysis: red blood cells—often associated with red blood cell casts, proteinuria, and polymorphonuclear leukocytes.
Elevated ASO titer.
Complement level: C3 level initially decreased; returns to normal 6 to 8 weeks after presentation (sometimes sooner).
Throat culture positive for group A streptococcus can confirm diagnosis.
Penicillin: a 10-day course.
Cephalosporins or macrolide antibiotics can be used in patients with penicillin allergy.
Acute renal insufficiency: furosemide.
Hypertension: antihypertensive agents and sodium restriction.
Renal Artery/Vein Thrombosis
Andrea M. Kline-Tilford
Formation of a thrombus in the renal artery or vein.
Most commonly associated with asphyxia, sepsis, shock, dehydration, hypercoagulable state, indwelling umbilical catheter, or maternal diabetes in newborns/infants.
Also associated with nephrotic syndrome, congenital heart disease, inherited hypercoagulable state (e.g., Factor V Leiden deficiency), sepsis, exposure to contrast agents, or after kidney transplantation in children.
Clot formation as a result of endothelial cell injury or hypercoagulable/sludging state. Thrombus forms in the intrarenal circulation; may extend to inferior vena cava or main renal vein.
Renal artery thrombus: acute occlusion of the renal artery due to thrombus formation, leading to renal infarction and irreversible loss of renal function.
Abrupt onset of hematuria.
Flank mass, unilateral or bilateral.
Doppler ultrasound of kidneys is diagnostic.
Ultrasound: enlarged kidney(s) (early stages), atrophic kidney(s) (late stages).
Radionuclide study: minimal or no function in the affected kidney(s).
Abdominal CT: filling defect during venous phase after contrast administration.
Magnetic resonance venography may also be used; avoid administration of contrast.
Microangiopathic hemolytic anemia; thrombocytopenia in some cases.
Monitor and maintain fluid and electrolyte balance.
Blood pressure monitoring; antihypertensive agents.
If refractory to pharmacologic therapy, may require nephrectomy.
Treatment with anticoagulants (e.g., heparin) or thrombolytics (e.g., streptokinase, recombinant tissue plasminogen activator) is common, but controversial.
Inferior vena cava thrombus may require thrombectomy.
Treat underlying disease (e.g., nephrotic syndrome), if indicated.
Pulmonary embolism, renal atrophy (affected side).
Renal Tubular Acidosis
Result of an inherited or acquired defect that affects the kidneys’ ability to filter bicarbonate or excrete ammonia.
Sickle cell anemia can be a genetic cause of renal tubular acidosis (RTA).
Acquired causes: certain medications, obstructive uropathy, and autoimmune diseases.
Often associated with presence of a UTI.
A relatively uncommon clinical syndrome characterized by defects in the renal tubules as a result of failure to maintain a normal serum bicarbonate level despite the consumption of a regular diet and normal metabolism and acid production.
Defects in renal tubules lead to a hyperchloremic metabolic acidosis, with a normal to moderately decreased GFR and normal anion gap.
Type I RTA (distal): decrease in acid excretion.
Type II RTA (proximal): failure of bicarbonate reabsorption with decreased ammonium absorption.
Type IV RTA: aldosterone deficiency or impairment of its effects, resulting in reduced potassium excretion, hyperkalemia, and acidosis.
Types I and II are most common in children.
Preference of savory foods.
Presentation of Specific Types
Type I RTA: linked to multiple genetic disorders (sensorineural hearing loss and nephrocalcinosis); failure to thrive or short stature, anorexia, vomiting, and dehydration.
Type II RTA: failure to thrive, hyperchloremic acidosis with hypokalemia, and rarely nephrocalcinosis; rickets or osteomalacia may indicate Fanconi syndrome.
Type III RTA: no longer used as a classification; now thought to be a combination of types I and II.
Type IV RTA: Hypertension common if child has underlying Gordon syndrome, renal parenchymal disease, or mineralocorticoid dysfunction.
Serum and urine electrolytes.
Fractional excretion of bicarbonate and urine pH.
Urine glucose and protein, calcium-to-creatinine ratio.
24-hour urine sample (i.e., citrate, calcium, potassium, and oxalate).
Radiographies of long bone or wrists for evaluation of rickets.
Abdominal ultrasound (kidneys).
Genetic or chromosomal evaluation.
Emergency or impatient management for children with hyperchloremic, non-anion gap acidosis requiring bicarbonate replacement intravenously.
Slow rehydration and electrolyte replacement, sodium bicarbonate or citrate, diuretic, phosphate replacements in children with rickets.
Without proper therapy, chronic acidity in the blood results in growth retardation, nephrolithiasis, bone disease, and chronic renal failure.
Hemolytic Uremic Syndrome
Tamara L. Hill
HUS is the most common cause of acute renal failure (ARF) in children <4 years of age.
Characterized by the simultaneous occurrence of microangiopathic hemolytic anemia, thrombocytopenia, and uremia.
Divided into Shiga-toxin-associated HUS and non-Shiga-toxin-associated HUS based on clinical presentation.
Shiga-toxin-associated HUS occurs after a prodromal episode of bloody diarrhea caused by E. coli infection.
Non-Shiga-toxin-associated HUS is distinguished by absence of diarrhea or Shiga-toxin-producing E. coli infection, but with microangiopathic hemolytic anemia, thrombocytopenia, and uremia.
Gastroenteritis with fever, vomiting, diarrhea, abdominal pain, and diarrhea that begins as watery but then becomes bloody.
Physical examination: dehydration, edema, petechiae, hepatosplenomegaly, and marked irritability.
Hemoglobin level is commonly 5 to 9 g/dL.
Peripheral blood smear reveals helmet cells, burr cells, and fragmented red blood cells.
Reticulocyte count is moderately elevated.
Coombs test result is negative.
Significant leukocytosis with the leukocyte count greater than 300,000/mm3.
Aggressive management of fluids, electrolytes, and nutrition.
Control of hypertension and early initiation of dialysis have been associated with a decrease in mortality.
Tamara L. Hill
Kidney filtration disorder in which too much protein is filtered out of the blood, leaking into the urine.
Results in proteinuria, edema, and hyperlipidemia.
Believed to have immunopathogenesis.
Secondary causes include infection, drugs, immunologic/allergic disorders, association with malignant disease, glomerular filtration.
Box 16.3 Causes of Childhood Nephrotic Syndrome
Minimal change disease.
Focal segmental glomerulosclerosis.
Hepatitis B or C.
Human immunodeficiency syndrome.
Congenital syphilis, toxoplasmosis, cytomegalovirus, rubella.
Certain medications: penicillamine, gold, nonsteroidal anti-inflammatory medications, interferon, mercury, pamidronate, lithium.
Nail-patella syndrome, Pierson syndrome, and others.
Injury to the basement membrane epithelial cells (podocytes) which causes collapse of the podocyte structure, spacing, and fracture of the protein barrier, allowing negatively charged proteins to move free across this disrupted filtration membrane.
Results in proteinuria, edema, and decreased circulating albumin causing increased interstitial edema.
Increased synthesis of lipoproteins and decreased lipid catabolism.
Edema: most notably, periorbital edema.
Frothy or foamy urine.
Sudden increase in weight with edema.
Urine dipstick to determine proteinuria (rapid).
24-hour urine collection (ideal).
CBC with differential.
Complete metabolic panel with serum albumin.
Serum C3/C4 complement.
Hepatitis B and C.
Immunologic studies (IgG, IgM, IgE).
High-dose steroids (prednisone 2 mg/kg/day for 6 weeks divided into three doses).
Treatment continues until patient is in remission (3 days with zero-trace protein via urine dipstick).
Once proteinuria is resolved, maintenance dose of steroids—2 mg/kg every other morning, then tapered off over 6 weeks.
If no remission after initial treatment, patient is considered steroid-resistant. Begin cytotoxic medications such as cyclosporine A, cyclophosphamide, or chlorambucil.
Supportive therapy includes ACE inhibitors, statins, and diuretics, and restricting dietary sodium to 1,500 to 2,000 mg/day.
Hallmark of nephrotic syndrome is massive proteinuria and decreased circulating albumin levels.
Henoch-Schönlein Purpura Nephritis
Tamara L. Hill
Systemic vasculitis of the small vessels.
Henoch-Schönlein purpura nephritis and IgA nephropathy are similar in renal pathologic findings, but systemic findings are noted only in the former.
Occurs at any age from infancy to adulthood, but is overwhelmingly a childhood disease.
Approximately 14 to 15 cases per 100,000 population.
Appears to be mediated by the formation of immune complexes containing IgA within the skin, intestines, and glomeruli.
Symptoms usually present 1 to 3 weeks after an upper respiratory tract infection or gastrointestinal infection (e.g., Epstein-Barr virus, parvovirus B19, Helicobacter pylori infection, Yersinia infection, Shigella infection, Salmonella infection), or environmental allergen exposure (e.g., medications, foods, insect bites).
Raised, nonblanching, purpuric rash, most prominent on the buttocks and lower legs.
Presentation may be acute or insidious.
Urinalysis: microscopic or gross hematuria and proteinuria.
CBC: leukocytosis with eosinophilia, thrombocytosis.
Prothrombin time and activate partial thromboplastin time: decreased.
IgA levels: may be increased.
Stool guaiac test: occult blood.
Kidney biopsy findings are indistinguishable from those of IgA nephropathy.
Resolves spontaneously in >90% of patients.
Symptomatic management of systemic complications is the treatment of choice.
Prednisone 1 to 2 mg/kg/day for 14 days in some cases (more severe).
Plasmapheresis, high-dose IV immunoglobulin (IVIG), and immunosuppressant therapy may be needed for refractory cases.
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