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Chapter 39. Acidification of the Urine & Bicarbonate Excretion

A 50-year-old man comes to see his primary care physician complaining of back pain and fatigue. His physician diagnoses him with multiple myeloma. He also has secondary light chain nephropathy that causes him to have chronic metabolic acidosis due to a reduction in proximal tubular reabsorption of bicarbonate. Assuming the man has no other renal disease and that his lung function is normal, which of the following responses is most likely seen in the patient?

A. Increase in NH4+ in urine.

B. Decreased synthesis of glutamine in the liver.

C. Decrease in H2PO4 in the urine.

D. Increase in arterial Pco2.

The correct answer is A. Metabolic acidosis stimulates renal ammoniagenesis and allows a net increase in H+ excretion when NH4+ is lost in the urine. In chronic acidosis, the liver synthesis of glutamine is increased so that more NH4+ is produced, ruling out B. Increases rather than decreases in H2PO4 (C) and arterial Pco2 (D) would be associated with chronic metabolic acidosis.

A 25-year-old woman comes to the urgent care clinic complaining of burning on urination and needing to void frequently. She states she had a urinary tract infection (UTI) 2 years previously. On physical examination, the physician finds no suprapubic tenderness, and she is taking no medications. He orders a urinalysis to determine if a UTI is present. What is the lowest urinary pH that the physician would expect to see in the results of the urinalysis of this woman?

A. 2.5

B. 4.5

C. 6.5

D. 8.5

The correct answer is B. Typical urinary pH can vary widely between 4.5 and 8.0, but is usually around 6. Certain bacteria associated with UTIs (eg, Proteus sp.) produce urease, an enzyme that produces NH4+ from uric acid resulting in an increased urine pH upon infection. In contrast, Escherichia coli, a common cause of UTI, has no effect on urine pH.

A 22-year-old woman arrives at the urgent care clinic complaining of lethargy and weakness. Upon examination, her blood pressure was 100/55 mm Hg, and her body mass index was 17 kg/m2. She was taking no medications, had no significant medical history and denied any recent illness. She mentioned to the physician that she was afraid of ...

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