Can sustained marked hyperglycemia cause osmotic diuresis, volume depletion, and impaired microvascular perfusion?

Marked sustained hyperglycemia has two clinically important, convergent effects: glucosuria-driven fluid loss and vascular endothelial dysfunction. This is especially relevant in older adults, who may be more vulnerable to dehydration and reduced circulating volume during hyperosmolar hyperglycemic states (HHS).

Clinical and hemodynamic evidence

• When filtered glucose exceeds tubular reabsorptive capacity, glucose enters urine and retains water, producing osmotic diuresis. While the often-cited threshold is ~180–200 mg/dL, it varies; glucosuria is more consistent around 270–290 mg/dL.
• If drinking does not replace urinary losses, volume depletion follows. In HHS, estimated fluid deficits are ~100–220 mL/kg—approximately 10–22 L in a 100-kg adult—and can worsen renal function, serum hyperosmolality, and cognitive impairment.
• Plasma-volume contraction raises hematocrit and can increase whole-blood viscosity. This provides a supported, though less directly studied, route by which dehydration worsens blood rheology.

Endothelial and microvascular mechanisms

• Hyperglycemia impairs endothelial-dependent vasodilation and microvascular reactivity. A meta-analysis of 39 studies (1,065 participants) found overall endothelial impairment with acute hyperglycemia, particularly in macrovessels.
• Excess glucose promotes reactive oxygen species, AGE–RAGE signaling, and diacylglycerol–PKC activation, reducing nitric-oxide bioavailability and disrupting endothelial signaling, glycocalyx, and antithrombotic functions.
• Reduced nitric-oxide-mediated vasodilatory reserve can directly impair microvascular perfusion. Higher hematocrit, red-cell aggregation, and impaired red-cell deformability could further increase resistance in small vessels, although this complete sequence has not been directly demonstrated in human studies.

Clinical implications

• Severe dehydration can reduce cerebral perfusion, a particular concern when hyperglycemia is accompanied by confusion or other neurologic symptoms.

Bottom line

• The claim is substantially supported: marked sustained hyperglycemia can cause osmotic diuresis, major volume depletion, and endothelial dysfunction; these processes can plausibly compound impaired rheology and microvascular perfusion, though the full rheology-to-perfusion pathway remains less directly established.