Prolonged storage of a specimen tends to cause which primary change?

• A. Increased pCO2
• B. Decreased pO2
• C. Increased pO2
• D. Decreased pH

Answer: (A)

When a specimen is stored for an extended period, metabolic activity inside the sample continues, producing carbon dioxide. In a sealed or poorly ventilated sample, this CO2 accumulates, causing the partial pressure of CO2 (pCO2) to rise. The increasing CO2 also drives the formation of carbonic acid, lowering the pH. Oxygen is consumed during metabolism, so pO2 tends to decrease as well, but the most direct and primary change observed is the rise in pCO2. That’s why increased pCO2 is the best answer.