Acidosis and Alkalosis
Tests
Testing is used to identify whether a patient has an acid-base disorder, to determine how severe the disorder is, and to help diagnose underlying diseases such as diabetic ketoacidosis or the poisoning, that can cause acid-base disorders. Testing is also done to monitor critically ill patients, as well as patients with long term diseases of acid-base balance, such as chronic lung disease and kidney disease. The primary tests used to identify, evaluate, and monitor acid-base disorders are blood gases and electrolytes.
Blood gases are a group of tests performed together on an arterial blood sample (blood obtained from an artery instead of a vein). They are a snapshot of the blood’s pH, the amount of oxygen dissolved in the blood (PO2), and the amount of carbon dioxide dissolved in the blood (PCO2). Using these results the amount of bicarbonate in the blood (HCO3-) can be calculated.
Results seen:
| Acid-Base Disorder | H+ | pH | HCO3- | PCO2 | Body Compensation |
|---|---|---|---|---|---|
| Metabolic acidosis | ↑ | ↓ | ↓↓ | ↓ | Increased breathing rate (hyperventilation) to increase CO2 elimination |
| Metabolic alkalosis | ↓ | ↑ | ↑↑ | ↑ | Slowed breathing (hypoventilation) to decrease CO2 elimination |
| Respiratory acidosis | ↑ | ↓ | ↑ | ↑↑ | Kidney increases production of HCO3- and excretion of H+ (acid) |
| Respiratory alkalosis | ↓ | ↑ | ↓ | ↓↓ | Decreased production of HCO3- and excretion of H+ |
| ↑ increased level; ↑↑ greatly increased level; ↓ decreased level; ↓↓ greatly decreased level | |||||
Electrolytes refers to a group of four tests: Na+ (sodium), K+ (potassium), Cl- (chloride) and bicarbonate (total carbon dioxide content).
An anion gap can be calculated from the electrolytes and provides a clue to the cause of the acid/base imbalance.
Depending on the suspected cause, a number of other tests may be requested: Renal profile, glucose ketones in blood and ketones in urine, lactate, aspirin (salicylate), ethylene glycol, and methanol, to name a few.
