Which serum constituent is unstable if a blood specimen is left standing at room temperature for 8 hours before processing?

• A. Cholesterol
• B. Triglycerides
• C. Creatinine
• D. Glucose

Answer: (D)

Glucose is unstable because the cells still present in a blood sample continue to metabolize it through glycolysis after collection. When the specimen sits at room temperature for many hours, glucose is consumed to produce energy, so the measured glucose concentration decreases. This is why prompt processing or cooling the sample (often with glycolysis-inhibiting additives) is important to preserve the true glucose level.

Cholesterol, triglycerides, and creatinine don’t change appreciably with eight hours of standing at room temperature, so they’re not the constituents that exhibit instability under these conditions.