Renal Tubule Functional Disorders

by / Monday, 28 June 2010 / Published in Internal Medicine

  1. Renal Tubular Acidosis
  2. Diabetes Insipidus
  3. Syndrome of Inappropriate Antidiuretic Hormone


Renal Tubular Acidosis:

Type Characteristic Urinary pH
Type I A defect of the distal tubule (H+ gradient) >5.5
Type II Proximal tubule fails to resorb HCO3 >5.5 early then <5.5 as the acidosis worsens
Type IV ß Aldosterone (leading to hyper K+ and hyper Cl-

From ß secretion seen in DM, interstitial nephritis, ACEI’s, heparin, and NSAID use.

May also be due to aldosterone resistance from sickle cell or urinary obstruction


Diabetes Insipidus:

There is central and nephrogenic types of DI, both:

  • ß secretion of ADH if it is central diabetes insipidus, and an ADH resistance if it is nephrogenic

Signs and Symptoms of both:

  • Polyuria
  • Polydypsia
  • Nocturia
  • Urine osmolality £ 200 and serum osmolality ³ 300

Central DI:

  • Is either idiopathic (Primary) or caused by insult to brain (Secondary)
  • Treat this with DDAVP nasal spray

Nephrogenic DI:

  • Is an x-linked disease and may be secondary to sickle cell, pyelonephritis, nephrosis, amyloidosis, multiple myeloma drugs
  • Treat by increasing water intake and restricting sodium intake


  • With DDAVP administration, central DI will have a fast decrease in urine output, while nephrogenic DI will have no change in urine volume
  • With DDAVP administration, central DI shows an acute increase in urine osmolality, where nephrogenic DI shows no change in osmolality
  • Treat central DI with DDAVP or vasopressin
  • Treat nephrogenic DI by correcting the underlying cause (electrolyte imbalances).

Syndrome of Inappropriate Antidiuretic Hormone (SIADH):

There are many possible causes of SIADH:

  • CNS disease: trauma, tumors, hydrocephalus
  • Pulmonary diseases: pneumonia, Small cell carcinoma of lung, abscess, COPD
  • Endocrine disease: hypothyroidism, Conn’s syndrome
  • Drugs: NSAIDs, chemotherapy, diuretics, phenothiazine, oral hypoglycemics

Diagnosis:  presence of hyponatremia with a urine osmolality of >300mmol/kg

Treatment: this condition is usually self-limiting, resistant cases may require demeclocycline which induces nephrogenic DI

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