A 35-year-old male has presented to the Emergency Department with weakness and constipation. Whilst in the Emergency Department he had the following results:

Test

Value

Normal Adult Range

Sodium

138 mmol/L

135 – 145

Potassium*

2.6 mmol/L

3.2 – 4.5

Chloride*

119 mmol/L

100 – 110

Bicarbonate*

10 mmol/L

24 – 32

Glucose

5.5 mmol/L

3.0-6.0

Urea

6.4 mmol/L

2.7 – 8.0

Creatinine

98 μmol/L

65-115

Urine Sodium

35

Urine Potassium

50

Urine Chloride

45

Give the likely cause of this disturbance and the rationale for your answer. 

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College Answer

Distal (Type 1) RTA 
Hyperchloraemic, normal AG acidosis and severe hypoK, with normal renal function and positive urinary anion gap.

Discussion

Let us dissect these results systematically.

  1. The A-a gradient cannot be calculated, for lack of relevant bits.
  2. There is no pH recorded
  3. There is no PaCO2 recorded
  4. The SBE is not offered, but the bicarbonate is very low, suggesting a metabolic acidosis
  5. The respiratory compensation cannot be assessed
  6. The anion gap is normal:
    (138) - (119 + 10) = 9, or 11.6 when calculated with potassium
  7. Urinary pH is not supplied, but the urinary anion gap can be calculated: (35+50) - 45 = 40
    The high urinary anion gap (ie. evidence that chloride excretion is sub-optimal) suggests that a renal tubular acidosis is at play.

Given the extremely low bicarbonate value, and the hypokalemia, one might be tempted to call it a Type 1 (distal) renal tubular acidosis. Type 4 typically has a high potassium.

References

Batlle, Daniel C., et al. "The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis." New England Journal of Medicine 318.10 (1988): 594-599.

Corey, Howard E., Alfredo Vallo, and Juan Rodríguez-Soriano. "An analysis of renal tubular acidosis by the Stewart method." Pediatric Nephrology 21.2 (2006): 206-211.

Soriano, Juan Rodríguez. "Renal tubular acidosis: the clinical entity." Journal of the American Society of Nephrology 13.8 (2002): 2160-2170.

Karet, Fiona E. "Mechanisms in hyperkalemic renal tubular acidosis." Journal of the American Society of Nephrology 20.2 (2009): 251-254.

Batlle, D. C., S. Sabatini, and N. A. Kurtzman. "On the mechanism of toluene-induced renal tubular acidosis." Nephron 49.3 (1988): 210-218.