Chapter 24: Kidney & Urinary Tract

EVALUATION OF THE KIDNEY & URINARY TRACT

HISTORY

When renal disease is suspected, the history should include the following:

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

2. Rashes or joint pain/swelling

3. Growth delay or failure to thrive

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

5. Documentation of hematuria, proteinuria, or discolored urine

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

7. Sudden weight gain or loss or edema

8. Drug or toxin exposure

9. 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

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

PHYSICAL EXAMINATION

Important aspects of the physical examination include the height, weight, growth percentiles, skin lesions (café au lait, 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 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.

LABORATORY EVALUATION OF RENAL FUNCTION

Serum Analysis

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 is an additional indicator of glomerular function, independent of muscle mass. Cystatin C is a cysteine protease inhibitor that is produced by all nucleated cells and released in the blood. It is reabsorbed and catabolized by renal tubular cells. Currently, Cystatin C is less widely available, and is 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, pH, calcium, phosphorus, magnesium, albumin, or complement.

Glomerular Filtration Rate

The endogenous creatinine clearance (C_Cr) in milliliters per minute estimates the GFR. A 24-hour urine collection ...