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EVALUATION OF THE KIDNEY & URINARY TRACT
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When renal disease is suspected, the history should include the following:
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Preceding acute or chronic illnesses (eg, urinary tract infection [UTI], pharyngitis, impetigo, endocarditis, shunt infection, systemic lupus erythematosus [SLE])
Rashes or joint pain/swelling
Growth delay or failure to thrive
Polyuria, polydipsia, enuresis, urinary frequency, or dysuria
Documentation of hematuria, proteinuria, or discolored urine
Pain (abdominal, costovertebral angle, or flank)
Sudden weight gain or loss or edema
Drug or toxin exposure
Perinatal history including prenatal ultrasonographic studies, oligo- or polyhydramnios, birth asphyxia, dysmorphic features and other congenital anomalies, abdominal masses, voiding patterns, and umbilical artery catheterization
Family history of kidney disease, hypertension, deafness, dialysis, or renal transplantation
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Important aspects of the physical examination include the height, weight, growth percentiles, skin lesions (café au lait, ash leaf spots, purpura or rash), pallor, edema, or skeletal deformities. Anomalies of the ears, eyes, or external genitalia may be associated with renal anomalies or disease. The blood pressure should be measured in a quiet setting with a manual cuff of the appropriate size in the right upper extremity, ideally with the child seated with feet flat on the ground. The cuff should cover two-thirds of the child’s upper arm, and peripheral pulses should be assessed. The abdomen should be palpated and auscultated, with attention to nephromegaly, abdominal masses, musculature, ascites, or bruits.
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LABORATORY EVALUATION OF RENAL FUNCTION
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The standard indicators of renal function are serum levels of urea nitrogen and creatinine; their ratio is normally about 10:1. This ratio may increase when renal perfusion or urine flow is decreased, as in urinary tract obstruction or dehydration. Because serum urea nitrogen levels are more affected by these and other factors (eg, nitrogen intake, catabolism, use of corticosteroids) than are creatinine levels, the most reliable single indicator of glomerular function is the serum level of creatinine. Normative values for serum creatinine relate to muscle mass, and the generation of creatinine may be affected by age, sex, malnutrition, chronic illness, and amputation. At birth, serum creatinine reflects the mother’s creatinine level and declines over the first 1–2 weeks to reach a normal level for age. Serum cystatin C, a cysteine protease inhibitor that is produced by all nucleated cells and released in the blood, is an additional indicator of glomerular function, and levels are not affected by sex, height, or muscle mass. Cystatin C assays are less widely available, and they are less reliable in certain clinical settings, such as with corticosteroid administration or thyroid disease. Less precise but nonetheless important indicators of possible renal disease are abnormalities of serum electrolytes, bicarbonate, pH, calcium, phosphorus, magnesium, albumin, or complement.
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Glomerular Filtration Rate
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The endogenous creatinine clearance (CCr) in ...