Figure 416

A, Urinary acidification. Patients with hemoglobin SS or SC demonstrate an incomplete form of renal tubular acidosis. In response to a short-duration acid load, all of the patients studied by Goossens and coworkers [16] with otherwise normal renal function were unable to decrease urine pH below 5.3, whereas normal persons achieve a urinary pH of 5.0 or lower. Titrateable acid (TA) and total hydrogen ion excretion are lower in patients with Hb SS or Hb SC; however, in most cases, ammonia excretion is appropriate for the coexisting urine pH. The acidification defect has been classified as distal rather than proximal, because no associated wasting of bicarbonate occurs, and the acidification defect is characterized by failure to achieve a normal minimal urinary pH during acid loading. Investigators from several centers have found no evidence of metabolic acidosis in the absence of a sickle cell crisis; however, they have found changes consistent with mild chronic respiratory alkalosis [15].

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