From the Guidelines
Low bicarbonate levels in a healthy patient are most commonly caused by a Western diet characterized by high animal protein intake and low fruit and vegetable consumption, leading to a state of chronic low-grade metabolic acidosis, as evidenced by a 2017 study published in the American Journal of Kidney Diseases 1. This dietary pattern results in an imbalance between nonvolatile acids and the alkali needed to buffer these acids, with nonvolatile acids being produced through the metabolism of sulfur-containing amino acids found in animal protein, cereals, and grains.
- Key factors contributing to low bicarbonate levels include:
- High animal protein intake
- Low fruit and vegetable intake
- Metabolism of sulfur-containing amino acids
- Imbalance between nonvolatile acids and available alkali
- The condition can be treated with sodium bicarbonate supplementation or by increasing fruit and vegetable intake, with the latter yielding more benefits, as shown in a study where adults with stage 4 CKD experienced significant increases in plasma bicarbonate levels and decreases in net endogenous acid production and urinary endothelin 1 excretion after increasing their fruit and vegetable intake 1. Increasing fruit and vegetable intake is recommended as the first line of treatment for low bicarbonate levels, as it not only improves bicarbonate levels but also has additional health benefits such as decreasing systolic blood pressure and total-body weight, as demonstrated in the 2017 study 1.
From the Research
Causes of Low Bicarbonate (HCO3) Levels
- Low bicarbonate levels can be caused by various factors, including metabolic acidosis, chronic respiratory alkalosis, and mixed metabolic acidosis and chronic respiratory alkalosis 2
- Metabolic acidosis is a condition where the body produces too much acid or cannot effectively remove excess acid, leading to a decrease in bicarbonate levels
- Chronic respiratory alkalosis is a condition where the lungs remove too much carbon dioxide from the body, leading to an increase in blood pH and a decrease in bicarbonate levels
Association with Kidney Outcomes
- Low serum bicarbonate levels have been associated with an increased risk of acute kidney injury (AKI) and mortality in hospitalized patients 3, 4, 5
- A study found that patients with low serum bicarbonate levels were more likely to develop AKI and had a higher risk of mortality compared to those with normal serum bicarbonate levels 3
- Another study found that low bicarbonate levels were associated with a higher incidence of AKI and prolonged ICU stay in patients undergoing cardiac surgery 5
Normal Range and Kidney Outcomes
- Higher serum bicarbonate levels within the normal range have been associated with better survival and renal outcomes in African Americans 6
- A study found that each 1 mmol/l increase in serum bicarbonate within the normal range was associated with a reduced risk of death, dialysis, or GFR event 6
- However, the optimal serum bicarbonate level for kidney outcomes is not well established, and further studies are needed to clarify this relationship 6, 4