Reference Range

Dopamine is a monoamine neurotransmitter that belongs to the catecholamine family; the catecholamine family includes dopamine, norepinephrine, and epinephrine. Dopamine is mainly produced in the nervous system and adrenal medulla; it plays a role in many brain functions like behavior and cognition.

The plasma reference ranges for dopamine are as follows^[1]:

Supine adults: < 10 ng/ml (conventional units); < 0.065 nmol/L (SI units)
Ambulatory adults: < 20 ng/mL (conventional units); < 0.13 nmol/L (SI units)
Age 3-15 years: < 60 pg/mL (conventional units); < 0.39 nmol/L (SI units)

The urinary reference range for dopamine in adults and elderly persons is 65-400 mcg/24 hr.^[2]

The urinary reference ranges for dopamine in children are as follows^[2]:

0-1 year: 0-85 mcg/24 hr
1-2 years: 10-140 mcg/24 hr
2-4 years: 40-260 mcg/24 hr
>4 years: 65-400 mcg/24 hr

Interpretation

Catecholamines including dopamine may be elevated in the following instances:

After a medication withdrawal (eg, clonidine, alcohol)
In acute illness
With medications such as tricyclic antidepressants, buspirone, antipsychotic agents, cocaine, Levodopa, amphetamines, ephedrine, pseudoephedrine^[3]

Plasma

Patient instructions are as follows:

The patient should fast for at least 4 hours and should avoid smoking and caffeinated beverages.
Medication that interfere with catecholamines metabolism should be avoided if possible.

Specimen collection instructions are as follows:

An indwelling intravenous catheter should be used.
After catheter insertion, the patient should rest for 30 minutes in the supine position.
Withdraw the blood specimen afterward.

Collection tube - Lavender-top tube or green-top tube

Specimen preparation - Separate plasma from cells and transfer to transport tube in less than 1 hour and freeze immediately.

Storage/transport temperature - Frozen

Stability - Frozen (14 days)

Unacceptable conditions - Grossly hemolyzed specimens

Panels - Plasma fractionated catecholamines that include plasma dopamine, epinephrine, and norepinephrine

Urine

Patient instructions are as follows:

Medication that interfere with catecholamines metabolism should be stopped at least a week prior to the urine collection if possible.

Specimen collection - 24-hour urine collection, creatinine measurement on the same urine sample to assess the specimen adequacy

Collection container - Urine container with 25 mL 6N HCl preservative.

Specimen preparation: Separate plasma from cells and transfer to transport tube in less than 1 hour and freeze immediately.

Storage/transport temperature: Refrigerate during and after collection.

Stability - Room temperature: 3 days, refrigerated: 14 days, frozen: 14 days

Unacceptable conditions - A container with pH greater than 5

Panels - Catecholamines fractionation (free), 24-hour urine including urine dopamine, epinephrine, and norepinephrine

Description

Tyrosine hydroxylase converts tyrosine to 3,4-dihydroxyphenylalanine (DOPA), which is converted to dopamine under the effect of aromatic l-amino acid decarboxylase, then dopamine β-hydroxylase converts dopamine to norepinephrine and phenylethanolamine N -methyltransferase converts norepinephrine to epinephrine.^[6]

Indications/Applications

Plasma and/or urine dopamine tests are indicated as part of the work up for the diagnosis of the following conditions:

Plasma and/or urine dopamine can be used in the monitoring of the following conditions:

Adrenal incidentaloma
Neuroblastoma after therapy

Plasma fractionated catecholamines includes plasma dopamine, epinephrine, and norepinephrine, whereas 24-hour urine fractionated catecholamine includes urine dopamine, epinephrine, and norepinephrine.

In cases of pheochromocytoma, adrenal incidentaloma, and paraganglioma, plasma and urine dopamine must not be measured separately; rather, plasma fractionated catecholamines and 24-hour urine fractionated catecholamine should be ordered since rarely will pheochromocytomas and paragangliomas only secrete dopamine.

The most acceptable approach for pheochromocytoma diagnosis is to screen with 24-hour urine collection for fractionated metanephrines and catecholamines; if high clinical suspicion exists, then plasma fractionated metanephrines should then follow as a confirmatory test.

During the work-up for neuroblastoma, dopamine, whether in the urine or the plasma, should be measured in combination with 24-hour urine vanillylmandelic acid (VMA) and homovanillic acid (HVA).