Type of test Blood

Normal findings

 Normetanephrine: < 0.5 nmol/L or 18-111 pg/mL by high performance liquid chromatography (HPLC)

Metanephrine: < 0.9 nmol/L or 12-60 pg/mL by HPLC

(Results vary among laboratories.)

Test explanation and related physiology

Pheochromocytomas, although rarely a cause of hypertension, are potentially lethal tumors. They produce several catechol amines that can cause episodic or persistent hypertension that is unresponsive to conventional treatment. The current diagnosis of pheochromocytoma depends on biochemical evidence of catecholamine overproduction by the tumor. This blood test measures the amount of metanephrine and normetanephrine, which are metabolites of epinephrine and norepinephrine, respectively.

The high sensitivity of plasma free metanephrine testing pro vides a high negative predictive value to the test. This means that if the concentrations of the free metanephrines are normal in the blood, then it is very unlikely that a patient has a pheochromocytoma. In about 80% of patients with pheochromocytoma, the magnitude of increase in plasma free metanephrines is so large that the tumor can be confirmed with close to 100% probability. Intermediate concentrations of normetanephrine and metanephrine are considered indeterminate. Urinary testing may clarify indeterminate findings.

When interpreting results, the following may be helpful:

 • Any sample in which the concentrations of both normetanephrine and metanephrine are less than the upper reference range limit should be considered normal, and the presence of pheochromocytoma is highly unlikely.

• Any sample in which the concentrations of either normetanephrine or metanephrine exceed their respective upper reference range limits should be considered elevated.

• Whenever the normetanephrine or metanephrine con centration exceeds the indeterminate range, the presence of pheochromocytoma is highly probable and should be located via imaging techniques. Pheochromocytoma sup pression and provocative testing  may assist in identifying this tumor.

Interfering factors

• Increased levels may be caused by caffeine or alcohol.

• Vigorous exercise, stress, and starvation may cause increased metanephrine levels.

* Drugs that may cause increased metanephrine levels include epinephrine-containing or norepinephrine-containing drugs, levodopa, lithium, and nitroglycerin.

* Acetaminophen can interfere with HPLC testing of metanephrines and should be avoided for 48 hours before testing.

Procedure and patient care

Before

* Explain the procedure to the patient.

* Explain the dietary and medicinal restrictions.

During

• Identify and minimize factors contributing to patient stress.

 • Physical and emotional stress may alter test results.

 • The patient may be asked to lie down and rest quietly for 15 to 30 minutes before sample collection.

 • The blood sample may be collected while supine.

 • Collect a venous blood sample in a chilled lavender-top or pink-top tube. Invert to mix with preservatives.

 After

• Apply pressure to the venipuncture site.

 • Send the specimen to the laboratory as soon as the test is completed.

 Abnormal findings

 Increased levels

-Pheochromocytoma

اخر الاخبار

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المزيد

الآخبار الصحية

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لحماية أسنان طفلك.. هذا الفيتامين يقلل خطر التسوس

أكل الطعام بسرعة.. طريق سريع إلى أمراض خطيرة

المزيد

الآخبار التكنلوجية

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المزيد

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