What is the variability of plasma norepinephrine levels?

May 23, 2007 9:14 AM

Does plasma norepinephrine stay relatively constant, or does it fluctuate a lot?

Because of some physical symptoms, I suspect I might have high sympathetic nervous system activity. So, I got a prescription from my doctor for a plasma norepinephrine test. The only thing is that I'm wondering how much the test results will be affected by transient factors, such as time of day and momentary stress levels. In other words, is plasma NE comparably variable to, say, heart rate? If so, how can I get a reliable assessment of my levels of synaptic norepinephrine?

Note: I also got a prescription for 24-hour urine catecholamine levels, in case that's more useful.

posted by wireless to Health & Fitness (4 answers total)

I'd assume there is a normal NE basal concentration. From some quick digging it looks like 3.38nmol/L. (That was just some quick internet searching, so take with a grain of salt.) Obviously that varies with levels of stress. That's why they usually do a 24 hour catecholamine test instead so that the variation during the day is accounted for. (FYI: NE is a type of catecholamine.)
posted by ruwan at 10:36 AM on May 23, 2007

Just to be curious: did you just outright ask for those prescriptions, or did your doctor independently recommend the tests? Did he or she think they'd be useful? Realistically, it's your doctor's job to interpret the results, and to give you reasonable guidance in terms of both your expectations and the results themselves; I'd find it really odd if your physician prescribed the tests but didn't have any idea how to interpret them.

(And the short answer to your question is that yes, the levels vary a lot and aren't that useful to measure except in the case of tightly-controlled situations like tilt-table tests, or in the case of massively elevated situations like catecholamine-producing tumors like neuroblastoma, adrenal tumors, and the like.)
posted by delfuego at 12:27 PM on May 23, 2007

Labtestsonline and the Labcorp website have lots of info on the catecholamine tests. My understanding was that the test was only performed to diagnose adrenal tumors.

It also looks like it's highly sensitive to all the factors you describe.
posted by euphorb at 5:57 PM on May 23, 2007

I once had some tests run on my epinephrine levels in an effort to determine whether my adrenal gland was operating properly. I learned two relevant things. 1. If they're on the high end of the normal range, then that means they're probably elevated due to stress, anxiety, that sort of thing. 2. If they're in the high range, that means you might have Addison's, a tumor, or some other biological condition that would cause your adrenal gland to overproduce. So the test could certainly distinguish between an actual endocrine disease and plain old fashioned anxiety.

I'm sorry, I don't remember where the numerical cut offs were for "normal" and "high." If you can't get answers elesewhere, email me (address in profile) and I'll sift through my medical records. I might be able to find something useful.

Best of luck.
posted by Clay201 at 10:20 PM on May 23, 2007