Definition

 • Kidney disease can present with variable combinations of proteinuria (above the upper limit of normal, usually defined by a urinary protein to creatinine ratio of >50 mg/ mmol), and/ or macro- or micro- haematuria, with or without acute or chronic renal dysfunction.

 Aetiology

 • Primary renal diseases, most commonly glomerulonephritides, tubulointerstitial diseases, either acquired or inherited.

• Systemic diseases can also present with isolated urinary abnormalities (e.g. early stages of diabetic nephropathy present with non- nephrotic proteinuria; some forms of amyloidosis present with only low- level proteinuria and renal dysfunction).

• A biopsy may or may not be needed to determine the cause, depending on clinical and biochemical findings.

 • A biopsy is usually indicated in patients with haematuria with presence of acanthocytes or red blood cell casts with an elevated serum creatinine level or proteinuria; in patients with proteinuria >1 g/ d on multiple visits with no clear comorbidity (e.g. diabetes or hypertension), especially if accompanied by an increase in serum creatinine; and in patients with proteinuria>3 g/ d in the absence of diabetes or a rapid increase in proteinuria even in patients with diabetes.

• A biopsy is usually not necessary in the case of diabetic patients showing a typical clinical course of progressive proteinuria and CKD, or in patients with isolated haematuria with neither dysfunction nor proteinuria, who usually have a benign clinical course (other non- kidney diseases of the genitourinary tract will need to be excluded).

Pathogenesis

• Glomerular disease: dysfunction of the glomerular filtration barrier with leakage of protein and/ or red blood cells into the urine. Dysmorphic red blood cells and heavy proteinuria are suggestive of glomerular disease.

• Tubular epithelial cell injury can lead to low- level proteinuria and low- level haematuria.

Presentation

 • Can be asymptomatic and picked up at a routine medical examination (e.g. urinary dipstick test).

• Can be picked up through the appearance of macroscopic haematuria or frothy urine.

Biochemistry

 • Creatinine can be normal or elevated.

• Proteinuria may be present.

• Macro- or microhaematuria may be present.

Prognosis

 • Depends on the cause; see individual causes.