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Methemoglobin in Blood (MET HGB)

Met Hb, Hemoglobin

Test Codes

EPIC: LAB5349, MHGB

Department

Chemistry

Specimen Collection Criteria

Preferred Specimen Type:  Collect one Dark Green-top Lithium or Sodium Heparin tube. (Minimum Whole Blood: 0.5 mL)

NOTE:  Do NOT use Light Green Plasma Separator (PST) tubes.

Acceptable Specimen Type: One blood gas syringe (see Blood Gas Procedure below).*

*NOTE: Blood Gas syringe specimens should ONLY be collected at the Dearborn, Farmington Hills, Grosse Pointe, Royal Oak, Taylor, Trenton, Troy, or Wayne Hospital Campuses. Specimens should NOT be collected at any other Beaumont Laboratory drawsite, Nursing Home, or Outreach office. 

Collection Procedure for Blood Gas Syringes ONLY: 

• A 1 mL or 3 mL plastic syringe containing dry heparin is usually used to collect the specimen.
• At least 1-2 mL (0.3 mL for pediatric patients) of blood is needed to ensure proper assay.
• Arterial specimens are collected by a physician, nurse, or respiratory therapist.
• For specimens collected by syringe, any air bubbles present in the syringe must be immediately expelled, the needle removed, and the syringe tightly capped. The syringe is rolled between the palms of the hands to ensure mixing.
  • Note: The Radiometer safePico Self-fill™ syringe has a metal ball to ensure homogeneous mixing when the syringe is rolled between the palms of the hands.
• Characterization of oxygen enrichment, at the time of arterial puncture, is required. This may be expressed as FiO2 fractional inspired oxygen concentration provided (e.g., 0.50), FiO2% (e.g., 50%), room air, or nasal cannula flow rate in liters per minute. The FiO2 must be noted on the requisition or entered as part of the electronic order for any arterial blood gas specimens. FiO2 is not required for venous blood gas orders.
• The specimen must be properly labeled.
• Place on wet ice for transport. Ice and Specimen must be kept separated.
  • Suggested: Place specimen in front pocket of the biohazard bag. Place ice in zip lock section of biohazard bag.

• The specimen must be transported immediately to the STAT Laboratory (Royal Oak) or to the Chemistry Laboratories.   

Physician Office/Draw Specimen Preparation

For Lithium or Sodium Heparin tubes (Dark Green Tubes) ONLY:

DO NOT remove Vacutainer^® stopper. Arrange for transportation to the Laboratory immediately. Maintain whole blood specimen refrigerated (2-8°C or 36-46°F) prior to transport. (Minimum: 0.5 mL)

Preparation for Courier Transport

Transport: Whole blood specimen, refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL)

Rejection Criteria

• Specimens collected in fluoride or oxalate tubes.
• Clotted specimens.
• Specimens not collected and processed as indicated. 

Inpatient Specimen Preparation

• Transport Dark Green-top tubes to the Laboratory immediately.
• If a blood gas syringe specimen was collected, transport STAT, on wet ice, to the STAT Laboratory (Royal Oak) or the Chemistry Laboratories.  

In-Lab Processing

Dark Green-top tubes: Deliver immediately to the appropriate testing station. Maintain refrigerated (2-8°C or 36-46°F) prior to testing.

Blood Gas Syringe specimens: Immediately analyze the whole blood, heparinized, iced specimen upon receipt.

Storage

Specimen Stability for Testing:

Dark Green-top Heparin Tubes
Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 72 hours
Frozen (-20°C/-4°F or below): Unacceptable

Blood Gas Syringes
Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): 1 hour
Frozen (-20°C/-4°F or below): Unacceptable

Specimen Storage in Department Prior to Disposal:

Dark Green-top tubes: Refrigerated (2-8°C or 36-46°F) for 7 days.
Blood Gas Syringes: Specimens are disposed within 8 hours of testing.

Laboratory

Dearborn Chemistry Laboratory
Farmington Hills Chemistry Laboratory 
Grosse Pointe Chemistry Laboratory 
Lenox Main Laboratory
Livonia Main Laboratory
Royal Oak STAT Laboratory 
Troy Chemistry Laboratory
Taylor Chemistry Laboratory
Trenton Chemistry Laboratory
Wayne Chemistry Laboratory

Performed

Sunday – Saturday, 24 hours a day.
Routine results available within 4 hours.
STAT results available within 1 hour of receipt in the Laboratory.

Reference Range

0-2 % of total hemoglobin.

Test Methodology

Absorption Spectrophotometry.

Interpretation

Methemoglobin is an inactive, oxidized form of hemoglobin which does not contribute to the oxygen-carrying capacity of blood. Sulfhemoglobin at a concentration of approximately 10% decreases the Met Hgb reading by approximately 3.5%.
Methylene blue in a concentration of approximately 60mg/L blood strongly interferes with Met Hgb measurements, giving falsely low results (-17% for a blood sample with O₂SAT=100% and -6% for a sample with O₂SAT=0%).
Changes in pH directly influence Met Hgb results. The magnitude of effect depends on the Met Hgb level and the pH change.

Clinical Utility

This assay aids in the diagnosis of methemoglobinemia. Methemoglobinemia, with or without sulfhemogloblinemia, is most commonly encountered as a result of administration of such medications as phenacetin, phenazopyridine, sulfonamides, local anesthetics, dapsone, or following ingestion of nitrites or nitrates. Congenital methemoglobinemias are rare. In congenital methemoglobinemia, the methemoglobin concentration in blood is about 15-20% of total hemoglobin. These patients are mildly cyanotic and asymptomatic. In acquired (toxic) methemoglobinemia, the Met Hgb concentration may be much higher. Symptoms may be severe when methemoglobin is greater than 40% of hemoglobin. Very high methemoglobin concentrations may be fatal.

CPT Codes

83055, 83857.

Contacts

Last Updated

3/23/2023