American Board of Internal Medicine (ABIM) Certification Practice Exam

Which of the following best defines the "Δ-Δ ratio" in acid-base disturbance assessment?

1. Change in bicarbonate divided by the change in pH

2. Calculating the ratio of the change in the anion gap to the change in bicarbonate level

3. Change in serum sodium divided by the change in chloride

4. Ratio of serum urea nitrogen to creatinine

The correct answer is: Calculating the ratio of the change in the anion gap to the change in bicarbonate level

The "Δ-Δ ratio" is a clinical tool used to assess acid-base disturbances, particularly in cases of metabolic acidosis. It specifically refers to the ratio of the change in the anion gap to the change in bicarbonate level. This ratio helps clinicians understand whether the metabolic acidosis is purely due to a primary process affecting the bicarbonate level or if there is an additional metabolic disturbance. When calculating the Δ-Δ ratio, a clinician measures the change in the anion gap from normal values and compares it to the change in bicarbonate concentration from baseline values. If the changes correlate appropriately, the clinician can conclude that the acidosis is likely a simple primary process. Conversely, if there is a significant discrepancy between the two, it suggests that there may be additional metabolic processes at play – for instance, another process contributing to the acid-base disturbance, such as a superimposed respiratory acidosis or a renal tubular acidosis. Understanding this ratio can guide further diagnostic and therapeutic interventions, making it a valuable component of acid-base analysis in clinical practice. The other options listed do not pertain to the assessment of acid-base disturbances in the same manner as the Δ-Δ ratio.