What is the expected glucose concentration after 6 hours if a serum specimen with an initial glucose level of 200 milligrams per deciliter (mg/dL) is left unseparated on the clot at room temperature?

Expected Glucose Concentration After 6 Hours of Storage at Room Temperature

The expected glucose concentration after 6 hours would be approximately 140 mg/dL (option C) when a serum specimen with an initial glucose level of 200 mg/dL is left unseparated on the clot at room temperature.

Mechanism of Glucose Degradation

Glycolysis is the primary mechanism responsible for glucose degradation in blood samples. According to the most recent guidelines:

• The rate of glycolysis averages 5% to 7% (approximately 10 mg/dL) per hour 1
• This rate varies with glucose concentration, temperature, white blood cell count, and other factors 1
• When blood samples remain unseparated, cellular components continue to metabolize glucose through glycolysis

Calculation of Expected Glucose Decrease

For a sample with an initial glucose concentration of 200 mg/dL left at room temperature for 6 hours:

• Rate of glycolysis: 5-7% per hour or approximately 10 mg/dL per hour 1
• Total decrease over 6 hours: approximately 60 mg/dL
• Expected final concentration: 200 mg/dL - 60 mg/dL = 140 mg/dL

Factors Affecting Glycolysis Rate

Several factors influence the rate of glycolysis in stored blood samples:

• Higher ambient temperature accelerates glycolysis
• Higher initial glucose concentration can lead to faster degradation
• Higher white blood cell count increases glycolysis rate 1
• Presence or absence of glycolysis inhibitors

Prevention of Glycolysis in Clinical Practice

To minimize glycolysis in clinical settings, the following methods are recommended:

1. Immediate separation of plasma from blood cells - In separated, non-hemolyzed, sterile serum without fluoride, glucose concentration is stable for 8 hours at 25°C 1

2. Use of ice-water slurry - Placing the blood tube in an ice-water slurry immediately after collection and separating plasma within 30 minutes 1

3. Use of effective glycolysis inhibitors - Blood collection tubes containing citrate buffer, sodium fluoride, and EDTA are more effective than tubes with only sodium fluoride 1

Common Pitfalls in Glucose Measurement

• Relying solely on sodium fluoride as a glycolysis inhibitor - Fluoride alone does not prevent short-term glycolysis and is ineffective for up to 4 hours after collection 1
• Delayed processing of samples without proper temperature control
• Failure to recognize that glycolysis continues even after collection in standard tubes

In clinical laboratory practice, accurate glucose measurement is critical for diabetes diagnosis and management. Falsely low glucose values due to glycolysis can lead to missed diagnoses of diabetes in patients with borderline glucose levels 1.