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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 disease, hereditary nephritis, deafness, dialysis, or renal transplantation

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

  3. Rashes or joint pains

  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. Data pertaining to the newborn with suspected urinary tract disease: prenatal ultrasonographic studies, birth asphyxia, Apgar scores, oligohydramnios, dysmorphic features, abdominal masses, voiding patterns, anomalous development, and umbilical artery catheterization

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PHYSICAL EXAMINATION

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Important aspects of the physical examination include the height, weight, skin lesions (café au lait or ash leaf spots), 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. The cuff should cover two-thirds of the child's upper arm, and peripheral pulses should be noted. The abdomen should be palpated, with attention to the kidneys, abdominal masses, musculature, and the presence of ascites. An ultrasonic device is useful for measurements in infants.

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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 glomerular filtration rate. The serum creatinine level of small children should be well under 0.8 mg/dL. Only larger adolescents should have levels exceeding 1 mg/dL. 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 glomerular filtration rate (GFR). A 24-hour urine collection is the "classic" approach for determining creatinine clearance; however, it is often difficult to obtain in the pediatric population. 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 the time; and (2) putting all urine subsequently voided into the collection receptacle, including the last void, 24 hours later. Reliability of the 24-hour collection can be checked ...

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