From the Research
A norepinephrine level of 728 pg/mL is likely elevated and not normal, even for a patient on fludrocortisone. Fludrocortisone is a synthetic mineralocorticoid that increases sodium retention and blood pressure, but it typically doesn't directly increase norepinephrine levels to this degree. Normal plasma norepinephrine levels generally range from 70-750 pg/mL when supine, though laboratory reference ranges may vary. While fludrocortisone can indirectly affect the sympathetic nervous system through volume expansion and blood pressure changes, this medication wouldn't be expected to cause significant elevations in norepinephrine. An elevated norepinephrine level in a patient on fludrocortisone should prompt further evaluation for other causes, such as pheochromocytoma, neurogenic hypertension, medications that affect catecholamine levels, or improper sample collection (as standing position, stress, or recent exercise can temporarily increase catecholamine levels) 1. The clinical context and symptoms should guide interpretation of this laboratory value.
Some studies have shown that fludrocortisone can actually decrease plasma norepinephrine levels in healthy humans 2, or have no significant effect on norepinephrine levels in patients with chronic fatigue syndrome 3. However, the use of vasopressors, including norepinephrine, is common in critically ill patients with shock, and the choice of vasopressor depends on the individual patient's condition and the underlying cause of shock 1, 4. In general, norepinephrine is considered a first-line agent for the treatment of cardiogenic shock, and its use is supported by recent studies 4.
Key points to consider when interpreting a norepinephrine level in a patient on fludrocortisone include:
- The clinical context and symptoms of the patient
- The potential for other causes of elevated norepinephrine levels, such as pheochromocytoma or neurogenic hypertension
- The effects of fludrocortisone on the sympathetic nervous system and blood pressure
- The use of other medications that may affect catecholamine levels
- The potential for improper sample collection or laboratory error. Overall, a norepinephrine level of 728 pg/mL is likely elevated and warrants further evaluation, regardless of the patient's use of fludrocortisone.