What are the lab findings in contraction alkalosis?

From the Guidelines

Contraction alkalosis is characterized by specific laboratory findings, including elevated arterial pH (>7.45), increased serum bicarbonate (HCO3- >26 mEq/L), and elevated base excess, as well as decreased serum chloride (<98 mEq/L) and low potassium levels (<3.5 mEq/L) 1.

Key Laboratory Findings

• Elevated arterial pH (>7.45)
• Increased serum bicarbonate (HCO3- >26 mEq/L)
• Elevated base excess
• Decreased serum chloride (<98 mEq/L)
• Low potassium levels (<3.5 mEq/L)
• Urine chloride is typically low (<10 mEq/L) unless the cause is ongoing (as in diuretic use)

Pathophysiology

Contraction alkalosis results from a decrease in extracellular fluid volume without a proportional loss of bicarbonate, leading to an increase in bicarbonate concentration and a subsequent rise in arterial pH 1. The kidneys attempt to compensate by increasing renal hydrogen ion retention and bicarbonate excretion, but this compensation is often incomplete, leading to the persistent alkalosis seen in laboratory values.

Common Causes

• Vomiting
• Nasogastric suction
• Diuretic therapy
• Post-hypercapnic states

Clinical Considerations

It is essential to distinguish contraction alkalosis from other causes of metabolic alkalosis, such as Bartter syndrome, which can present with similar laboratory findings 1. A thorough clinical evaluation, including a detailed medical history and physical examination, is necessary to determine the underlying cause of the alkalosis.

From the Research

Lab Findings in Contraction Alkalosis

• Low serum sodium and chloride levels, and high serum carbon dioxide and bicarbonate levels are characteristic of contraction alkalosis 2
• Elevated serum CO2 and bicarbonate levels, with low serum chloride levels, are indicative of metabolic alkalosis, which can be a component of contraction alkalosis 3, 4, 5, 6
• Blood chemistry panels may reveal elevated serum CO2 and bicarbonate levels, with decreased serum chloride levels, in patients with contraction alkalosis 2, 4
• Arterial blood gas analysis may show an elevated pH, with a compensatory increase in PaCO2, in patients with metabolic alkalosis, including those with contraction alkalosis 3, 5, 6

Key Laboratory Features

• Elevated serum bicarbonate levels (>32 mEq/L) 2, 4
• Elevated serum CO2 levels (>32 mEq/L) 2, 4
• Low serum chloride levels (<94 mmol/L) 2, 4
• Elevated arterial pH (>7.45) 3, 5, 6
• Compensatory increase in PaCO2 3, 5, 6