The bicarbonate (serum) test is a blood test that measures the amount of bicarbonate (HCO3-) in your bloodstream. Bicarbonate is one of the body’s main electrolytes and acts as a buffer that helps keep your blood’s acid-base balance (pH) in a healthy range. On many lab reports, this value may also be shown as total CO2 because most carbon dioxide in the blood is present in the form of bicarbonate.

Your body constantly produces acids through normal metabolism, and your lungs and kidneys work together to remove acids and maintain a stable pH. The bicarbonate level provides an important clue about whether your body is trending toward too much acid (acidosis) or too much base (alkalosis).

In plain language:

Low bicarbonate often suggests your blood is more acidic than it should be (metabolic acidosis) or that bicarbonate is being lost from the body. This can happen with severe diarrhea, kidney problems, diabetic ketoacidosis, or other conditions that increase acid levels or reduce buffering.

High bicarbonate often suggests your blood is more alkaline than it should be (metabolic alkalosis) or that your body is retaining bicarbonate. This may occur with prolonged vomiting, dehydration, certain diuretics (“water pills”), or as compensation for long-term lung disease where carbon dioxide is retained.

Because bicarbonate is part of a broader electrolyte and acid-base system, doctors usually interpret it alongside other tests such as sodium, potassium, chloride, anion gap, creatinine, and sometimes arterial/venous blood gases.

Serum bicarbonate is commonly included in a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). Your clinician may order it to evaluate your overall metabolic health, kidney function, and acid-base status—especially when symptoms or medical history suggest an electrolyte or pH imbalance.

This test is often ordered if you have symptoms that could be related to an acid-base or electrolyte problem, such as:

• Unexplained fatigue, weakness, or confusion

• Rapid or deep breathing, shortness of breath, or feeling like you can’t catch your breath

• Nausea, vomiting, or ongoing diarrhea

• Dehydration, dizziness, or low blood pressure

• Muscle cramps, tingling, or irregular heartbeat symptoms (often evaluated with other electrolytes)

It’s also commonly used to help assess or monitor:

Kidney disease: The kidneys regulate bicarbonate; chronic kidney disease can lead to persistently low bicarbonate (metabolic acidosis).

Diabetes complications: In diabetic ketoacidosis (DKA), bicarbonate often drops as acids build up in the blood.

Lung (respiratory) conditions: With chronic lung diseases (for example, COPD), the body may retain CO2; the kidneys may compensate by increasing bicarbonate.

Medication effects: Diuretics, certain antacids, and other medicines can shift electrolytes and bicarbonate levels.

Emergency and hospital care: Bicarbonate is frequently checked in dehydration, sepsis, shock, severe infections, or suspected poisoning/overdose to evaluate metabolic status and calculate the anion gap.

• Chronic kidney disease (CKD) and kidney tubular disorders (renal tubular acidosis)
• Diabetic ketoacidosis (DKA) and other causes of ketoacidosis (including alcohol-related ketoacidosis)
• Lactic acidosis (e.g., from severe infection/sepsis, low oxygen states)
• Chronic obstructive pulmonary disease (COPD) with chronic CO2 retention
• Severe diarrhea or gastrointestinal bicarbonate loss
• Prolonged vomiting or gastric suction leading to metabolic alkalosis
• Dehydration and electrolyte imbalance related to diuretic use
• Poisoning/overdose affecting acid-base balance (e.g., salicylates/aspirin, toxic alcohols)

• Monitoring electrolytes and overall metabolic balance as part of routine wellness labs (BMP/CMP)
• Supporting kidney health monitoring, especially in chronic kidney disease or at-risk patients
• Helping track diabetes safety by identifying signs of metabolic acidosis during illness or poor glucose control
• Assessing hydration status and effects of vomiting/diarrhea on body chemistry
• Monitoring the impact of medications that affect electrolytes (such as diuretics)
• Evaluating and following acid-base balance during acute illness, hospital care, or recovery
• Supporting management of chronic lung conditions by providing clues about long-term CO2 retention and compensation