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EVALUATION OF THE KIDNEY & URINARY TRACT

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HISTORY

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When renal disease is suspected, the history should include

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  1. Family history of cystic renal disease, hypertension including early-onset, hereditary nephritis, deafness, dialysis, or renal transplantation

  2. Preceding acute or chronic illnesses (eg, urinary tract infection [UTI], pharyngitis, impetigo, endocarditis)

  3. Rashes or joint pain/swelling

  4. Growth delay or failure to thrive

  5. Polyuria, polydipsia, enuresis, urinary frequency, or dysuria

  6. Documentation of hematuria, proteinuria, or discolored urine

  7. Pain (abdominal, costovertebral angle, or flank) or trauma

  8. Sudden weight gain or edema

  9. Drug or toxin exposure

  10. Birth history including prenatal ultrasonographic studies, oligo- or polyhydramnios, birth asphyxia, dysmorphic features and other congenital anomalies, abdominal masses, voiding patterns, and umbilical artery catheterization

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PHYSICAL EXAMINATION

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Important aspects of the physical examination include the height, weight, growth percentiles, skin lesions (café au lait or ash leaf spots 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 in the right upper extremity. The cuff should cover two-thirds of the child’s upper arm, and peripheral pulses should be assessed. The abdomen should be palpated, with attention to nephromegaly, abdominal masses, musculature, and the presence of ascites.

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LABORATORY EVALUATION OF RENAL FUNCTION

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Serum Analysis
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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. For example, an increase in serum creatinine from 0.5 to 1.0 mg/dL represents a 50% decrease in GFR (glomerular filtration rate). Norms for serum creatinine relate to muscle mass. Therefore, only larger adolescents should have levels exceeding 1 mg/dL. Serum cystatin C has been proposed to be a more reliable indicator of glomerular function but is less widely available and with variable reference ranges in the pediatric population. Less precise but nonetheless important indicators of possible renal disease are abnormalities of serum electrolytes, pH, calcium, phosphorus, magnesium, albumin, or complement.

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Glomerular Filtration Rate
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The endogenous creatinine clearance (CCr) in milliliters per minute estimates the GFR. A 24-hour urine collection is the “classic” approach for determining creatinine clearance; however, it is often difficult to accurately obtain in the pediatric population, particularly in children who are not continent. The procedure for collecting a timed urine specimen should be explained carefully so that the parent or patient understands fully the rationale of (1) first emptying the bladder (discarding that urine) and noting ...

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