Proximal Renal Tubular Acidosis and Fanconi Syndrome Secondary to Tenofovir Disopyroxil Fumarat: Importance of Arterial Blood Gases Analysis in Differrential Diagnosis in Severe Hypokalemia

Proximal renal tubular acidosis (pRTA) may occur alone or with Fanconi syndrome and may be idiopathic or associated with many drugs and diseases. A 71-year-old female patient was admitted with persistent, symptomatic hypokalemia, who used tenofovir disoproxil fumarate (TDF) for chronic HBV infection. While the diagnosis could not be reached by venous blood gas analysis, arterial blood gas analysis showed isolated normal anion gap hypokalemic hyperchloremic metabolic acidosis, and hypomagnesemia, hypouricemia, and hypophosphatemia were detected in biochemistry, suggesting pRTA and Fanconi syndrome. Since other etiologic causes were excluded and the history was compatible, this was attributed to the use of TDF, and clinical and laboratory response was achieved when TDF was switched into tenofovir alfenamide (TAF). TDF-associated pRTA and Fanconi syndrome may occur independently from the duration of TDF use, and switching into TAF may control this complication without disrupting the treatment of HBV infection. Requesting arterial blood gas analysis at least once is in patients presenting with acid-base disorder is valuable and determining for differential diagnosis.