Methemoglobinemia laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Template:Aksiniya K. Stevasarova, M.D.
Overview
Congenital (Hereditary) Methemoglobinemia
There are three main congenital conditions that lead to methemoglobinemia:
1. Cytochrome b5 reductase deficiency and pyruvate kinase deficiency
3. Presence of abnormal hemoglobin.
Acquired or Acute Methemoglobinemia
Most common cause include different oxidant drugs, toxins or chemicals
Laboratory Findings
ABG Analysis
On routine ABG analysis the partial pressure of oxygen (PO2) value should in normal reference ranges in patients with methemoglobinemia. The reason lies in the fact that the ABG value represents the oxygen content in the plasma, and not the oxygen-carrying capacity of hemoglobin.
Co-oximetry
The co-oximeter is the most accurate device to measure methemoglobin. The newer generation devices can actually differentiate between methemoglobin, carboxyhemoglobin, oxyhemoglobin, deoxyhemoglobin, and also sulfhemoglobin.
Pulse oximetry
The pulse oximetry in methemoglobinemia patients will always show a value around 85%, regardless of the level of MetHb in the blood. This is very importan tot know as this value can be misleading especially in patients with very high MetHb levels Fortunately new multiwavelength pulse oximeters have been developed recently and they can detect the levels of MetHb more accurately.
In methemoglobinemia patients we often see the so called “saturation gap” which can help us diagnose the condition. The gap is calculated by subtracting the oxygen percentage from the ABG analysis (typically normal in methemoglobinemia patients 100%) from the percentage of oxygen saturation given by the pulse oximeter (always ~85% in methemoglobiemia patients). Saturaion gap more than 5 % is significant.
- ↑ {{ Rev Bras Anestesiol. 2008 Nov-Dec;58(6):651-64. Methemoglobinemia: from diagnosis to treatment. [Article in English, Portuguese] do Nascimento TS1, Pereira RO, de Mello HL, Costa J.pmid=PMID: 19082413}}
- ↑ {{ Conf Proc IEEE Eng Med Biol Soc. 2017 Jul;2017:4570-4573. doi: 10.1109/EMBC.2017.8037873. Three-wavelength method for the optical differentiation of methemoglobin and sulfhemoglobin in oxygenated blood. Van Leeuwen SR, Baranoski GVG, Kimmel BW. pmid=29060914 }}
- ↑ {{Toxicol Rev. 2003;22(1):13-27. Occupational methaemoglobinaemia. Mechanisms of production, features, diagnosis and management including the use of methylene blue. Bradberry SM1. pmid=14579544}}
- ↑ {{South Med J. 2011 Nov;104(11):757-61. doi: 10.1097/SMJ.0b013e318232139f. Methemoglobinemia: pathogenesis, diagnosis, and management. Skold A1, Cosco DL, Klein R. pmid=22024786 }}