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Definition, Etiology, Clinical FeaturesTop
Tubulopathy is an umbrella term that encompasses various disease processes affecting the renal tubules. Some of these include renal tubular acidosis (RTA) (with type 1, type 2, and type 4), tubular channel defects leading to salt-losing nephropathies, and nephrogenic diabetes insipidus. A majority of these diseases are acquired as a result of another disease process damaging the kidneys, and very rarely the etiology is genetic or inherited.
Tubulopathies can present in a variety of ways. Some patients are completely asymptomatic, whereas others may present with respiratory failure related to severe hypokalemic periodic paralysis.
Clinicians often consider RTA when a non–anion gap metabolic acidosis (NAGMA) is discovered in a patient with other electrolyte derangements and normal renal function or when the acidosis is found to be out of proportion to the degree of renal function. NAGMA can be caused by etiologies that are renal, extrarenal, or both.
RTA is characterized by tubular inability to maintain acid-base balance despite relatively well-preserved renal function. This can be due to either net bicarbonate loss or inability to excrete acid.
RTA is usually suspected following the establishment of a hyperchloremic NAGMA. Diagnosis requires measurement of urinary pH and urinary anion gap (UAG) to estimate urinary ammonium excretion. A low urinary ammonium excretion, indicated by a positive UAG, helps distinguish RTA from other causes of NAGMA that would also present with hypokalemia, such as diarrhea.