In the fasting state, arterial and capillary blood glucose concentrations vary from venous glucose concentration by approximately how many mg/dL (mmol/L)?

• A. 1 mg/dL (0.05 mmol/L)
• B. 5 mg/dL (0.27 mmol/L)
• C. 10 mg/dL (0.55 mmol/L)
• D. 15 mg/dL (0.82 mmol/L)

Answer: (B)

In the fasting state the difference between arterial, capillary, and venous glucose is very small because tissues aren’t rapidly consuming large amounts of glucose. Arterial blood delivers glucose freshly from absorption, and as it passes through the capillary bed, a small amount is taken up by tissues. By the time blood returns as venous, only a modest amount has been extracted, so the gap is limited. This results in a typical arterial/capillary vs venous gradient of about 5 mg/dL (0.27 mmol/L). In other words, arterial and capillary glucose are only slightly higher than venous glucose when fasting. After a meal, tissue uptake increases and the gradient can be larger.