Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (551 page)

   In acute uric acid nephropathy, uric acid-to-creatinine ratio (mg/mg) is >1.0 in a random urine sample, whereas in most forms of AKI with decreased urinary output the ratio is <1.0. Hyperkalemia, hyperphosphatemia, and hypocalcemia may also accompany acute uric acid nephropathy, especially when it is the result of severe tissue destruction (e.g., tumor lysis syndrome).

Suggested Reading

Wiederkehr MR, Moe OW. Uric acid nephrolithiasis: a systemic metabolic disorder.
Clinic Rev Bone Miner Metab.
2011;9:207–217.

   
CONGENITAL KIDNEY DISORDERS

ECTOPIC KIDNEY

   Ectopic kidney or renal ectopy is a birth defect in which a kidney is located below, above, or on the opposite side of its usual position. The incidence is 1:1,000.

   The ectopic kidney generally has decreased function compared to the normal kidney, but the majority of patients are asymptomatic. In symptomatic patients, findings are mainly related to associated complications such as urinary tract infections, kidney stones, obstruction, or kidney damage.

   Diagnosed by imaging studies.

HEREDITARY NEPHRITIS (ALPORT SYNDROME)

   A genetic disorder caused by mutations in the genes encoding the alpha chains of type IV collagen. Approximately 85% of cases are due to mutations in the
COL4A5
gene located on the X chromosome (X-linked inheritance), which encodes the α
₅
chain of type IV collagen. The remaining cases result from mutations at the
COL4A3/COL4A4
locus on chromosome 2, encoding the α
₃
and α
₄
chains of type IV collagen. Inheritance of Alport syndrome caused by these mutations is autosomal recessive or, much less commonly, autosomal dominant.

   The initial renal manifestation during childhood is persistent microscopic hematuria, which may become gross hematuria after upper respiratory infection. Later in life, patients demonstrate progressive renal insufficiency and proteinuria. ESRD may develop during adulthood.

   In addition to renal abnormalities, patients often exhibit systemic manifestations, the most common of which are hearing impairment and ocular abnormalities.

   Diagnosis is based on family history and the specific manifestations such as renal failure and hearing loss. Renal biopsy findings by electron microscopy are essential for the diagnosis.

Suggested Reading

Haas M. Alport syndrome and thin glomerular basement membrane nephropathy: a practical approach to diagnosis.
Arch Pathol Lab Med.
2009;133(2):224–232.

HORSESHOE KIDNEY

   This congenital disorder involves fusion of two kidneys across midline, usually at the lower poles.

   Incidence is 1 in 500 or less; higher in females with Turner syndrome (15%).