Tubular Acidification Defect in Adults with Sickle Cell Disease

Abstract

Background and objectives: Metabolic acidosis is a frequent manifestation of sickle cell disease but the mechanisms and determinants of this disorder are unknown. Our aim was to characterize urinary acidification capacity in adults with sickle cell disease and to identify potential factors associated with decreased capacity to acidify urine.

Design, setting, participants, & measurements: Among 25 adults with sickle cell disease and an eGFR of ≥60 ml/min per 1.73 m² from a single center in France, we performed an acute acidification test after simultaneous administration of furosemide and fludrocortisone. A normal response was defined as a decrease in urinary pH <5.3 and an increase in urinary ammonium excretion ≥33 µEq/min at one or more of the six time points after furosemide and fludrocortisone administration.

Results: Of the participants (median [interquartile range] age of 36 [24-43] years old, 17 women), 12 had a normal and 13 had an abnormal response to the test. Among these 13 participants, nine had normal baseline plasma bicarbonate concentration. Plasma aldosterone was within the normal range for all 13 participants with an abnormal response, making the diagnosis of type 4 tubular acidosis unlikely. The participants with an abnormal response to the test were significantly older, more frequently treated with oral bicarbonate, had a higher plasma uric acid concentration, higher hemolysis activity, lower eGFR, lower baseline plasma bicarbonate concentration, higher urine pH, lower urine ammonium ion excretion, and lower fasting urine osmolality than those with a normal response. Considering both groups, the maximum urinary ammonium ion excretion was positively correlated with fasting urine osmolality (r²=0.34, P=0.002), suggesting that participants with sickle cell disease and lower urine concentration capacity have lower urine acidification capacity.

Conclusions: Among adults with sickle cell disease, impaired urinary acidification capacity attributable to distal tubular dysfunction is common and associated with the severity of hyposthenuria.

Podcast: This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_12_10_CJN07830719.mp3.

Keywords: France; acidosis; adult; ammonium compounds; body fluids; epidermal growth factor receptor; fasting urine osmolality; fludrocortisone; furosemide; glomerular filtration rate; homeostasis; human EGFR protein; metabolic acidosis; renal insufficiency; sickle cell anemia; sickle cell disease; urinary tract.