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Metanephrines - plasma
Short Description : Metanephrines- Plasma
Also known as : [Plasma free metanephrines]

Plasma
Test performed by: LabPLUS High Performance Liquid Chromatography


Patient preparation: Smoking and caffeine may cause false-positive results. Blood sampling may be done in the sitting position, as for routine blood sampling. However, the specificity of the test is improved if the patient is rested supine for 30 min. with a pre-cannulated IV line.

SPECIMEN: 4 ml EDTA blood required. Heparinised blood not acceptable. If plasma renin and aldosterone are also being requested, 2 tubes should be sent.

Transport & storage:

The minimum acceptable volume is 0.5 mL plasma.

Place the sample at 4 o C after collection and centrifuge and separate as soon as possible, but must be within 6 hours.

If sample is transported the same day , send at 4 O C, If next day please freeze and transport frozen

Specimen Collection

EDTA

4 mL EDTA Plasma (Always Required)

Micro-EDTA

0.5 mL Paediatric Micro-EDTA Blood

Please collect 2 x micro-edta samples


Reference Intervals

Units: pmol/L

Uncertainty of measurement :

Normetanephrine 20%

Metanephrine 16%

Normetanephrine

Metanephrine

See diagnostic notes for age-based reference intervals. This varies based on patient preparation at time of sample collection.

< 500



Turnaround Time: Within 5 days
Assay Method

Principle : Liquid chromatography - tandem mass spectrometry


Diagnostic Use and Interpretation

This is a diagnostic test for phaeochromocytoma and paraganglioma . A negative result rules out a secretory tumour with high probability.
There is strong evidence to support the use of age-based reference ranges for the interpretation of the plasma normetanephrine concentration (1). False positive and false negative tests may still occur:
- Stress and acute, severe illness is associated with a physiological increase in metanephrines (2).
- Certain drugs including beta-blockers, noradrenaline reuptake inhibitors and tricyclic antidepressants may raise in vivo metanephrine levels and make interpretation difficult (2). It is recommended these drugs be withdrawn for at least 5 half-lives prior to testing if it is clinically appropriate to do so.
- Midodrine can cause falsely high plasma metanephrine levels due to interference in the LabPLUS assay. Urine metanephrines are not affected by this interference.
- Plasma free metanephrines are increased up to 2-fold in chronic renal failure, but are still useful for diagnosing phaeochromocytoma in this setting (3).
Age-based normetanephrine reference interval (supine, fasted patients)
Age (years)
Normetanephrine (pmol/L)
< 5
< 720
5 - 20
< 540
20 - 40
< 600
40 - 60
< 800
> 60
< 980
Interpretation of plasma metanephrines in non-fasted, non-supine (seated/ambulant) patients
An audit of local laboratory results and the subsequent diagnosis of phaeochromocytoma/paraganglioma has recommended the use of the following ranges in non-fasted, non-supine patients:
Age (years)
Normetanephrine (pmol/L)
< 30
< 900
30 - 40
< 1100
40 - 70
< 1200
> 70
< 1400
If there is on-going clinical suspicion of phaeochromocytoma/paraganglioma in a non-fasted, non-supine patient with a result between the two reference intervals, a follow-up test is recommended. This may be:
- Retest plasma metanephrines in a fasted patient who has been precannulated and allowed to rest supine for 20 minutes before a sample is taken via the IV cannula (2). This will require referral for outpatient collection or specialist endocrine review. LabTests does not provide this service. Collecting fasted, rested, supine samples generally results in a significantly lower normetanephrine level, hence the reference ranges are lower (1,4).
- 24-hour urine metanephrines ? a 24hr collect for urine metanephrines may be arranged through the laboratory. A raised urine level increases suspicion of phaeochromocytoma/paraganglioma, however it is slightly less sensitive than the fasted, rested, supine plasma test and so a small number of cases may be missed (5).
References:
1. Eisenhoffer, G., Lattke, P., Herberg, M. et al. 2013. Reference intervals for plasma free metanephrines with an age adjustment for normetanephrine for optimized laboratory testing of phaeochromocytoma. Ann Clin Biochem , 50(1): 62 ? 9.
2. Lenders, W., Duh, Q., Eisenhoffer, G. et al. 2014. Diagnosis and treatment of phaeochromocytoma and paraganglioma. JCEM , 6(1): 1915 ? 42.
3. Eisenhofer, G., Huysmans, F. et al. 2005. Plasma metanephrines in renal failure. Kidney Int , 67(2): 668 ? 77.
4. Darr, R., Pamporaki, C., Peitzsch, M. et al. 2013. Biochemical diagnosis of phaeochromocytoma using plasma?free normetanephrine, metanephrine and methoxytyramine: importance of supine sampling under fasting conditions. Clinical Endocrinology , 80(4): 478 ? 86.
5. Rifai, N., Horvath, R. & Wittwer, C. 2018. Tietz textbook of clinical chemistry and molecular diagnostics . St. Louis, MO: Elsevier.


Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.


Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427



Specimen Transport Instructions for Referring Laboratories

The minimum acceptable volume is 0.5 mL plasma.

Place the sample at 4 o C after collection and centrifuge and separate as soon as possible, but must be within 6 hours.

If sample is transported the same day , send at 4 o C , If next day please freeze and transport frozen



Last updated at 15:26:00 06/01/2025