A 68-year-old female is admitted to the hospital from an assisted living facility due to five days of severe, voluminous watery diarrhea. On presentation, she is lethargic with dry mucous membranes and delayed capillary refill. Her blood pressure is 88/54 mm Hg and her heart rate is 115/min. Laboratory studies are obtained:
| Test | Result |
|---|---|
| Serum sodium | 140 mEq/L |
| Serum potassium | 3.2 mEq/L |
| Serum chloride | 106 mEq/L |
| Serum bicarbonate | 14 mEq/L |
| Blood urea nitrogen | 58 mg/dL |
| Serum creatinine | 3.5 mg/dL |
Assuming a normal anion gap of 12 mEq/L and a normal serum bicarbonate of 24 mEq/L, what is this patient's delta-delta ratio ()?
Answer: 0.8
Answer
0.8
The patient's delta-delta ratio is 0.8. She has a high anion gap metabolic acidosis (HAGMA) due to acute kidney injury (uremia from hypovolemia) combined with a normal anion gap metabolic acidosis (NAGMA) driven by severe bicarbonate loss from diarrhea. In a pure HAGMA, for every 1 mEq/L increase in the anion gap, there should be a roughly 1 mEq/L drop in bicarbonate, resulting in a delta-delta ratio between 1.0 and 2.0. A ratio below 1.0 indicates that the bicarbonate has dropped more than expected for the degree of unmeasured anions, signaling an additional, concurrent non-anion gap metabolic acidosis.
Step-by-Step Solution
Key Concept
The delta-delta ratio () is utilized to identify mixed acid-base disorders in the presence of a high anion gap metabolic acidosis. A ratio < 1.0 (or < 0.8 depending on the criteria) suggests a concurrent normal anion gap metabolic acidosis.