Your question: My patient had a lab CO-Ox MethGB of 0.7 and later of 0.6. I know that the normal range is 0-1.5%, but what in the world is a CO-Ox MethGB? What does it measure and what does it effect?
My humble answer: Methemoglobiin is a type of hemoglobin that does not carry oxygen. It's normally 1-2% of all hemoglobin. Anything less than 10% will show no symptoms, so the fact a MetHb falls from 0.7 to 0.6 is insignificant. A variation of that amount might simply be a normal variation by the machine. As it gets high it just means that there is that much less hemoglobin for oxygen to attach to. If the methb gets higher than 10% you will note that the SpO2 will start to drop, and may read in the 90% range. As it gets higher the SpO2 will continue to drop. High methgb may = hypoxia.
For MetHb to be high is very rare, and I have never seen it in 15 years as an RT. There are a few rare disease states that prevent the body from converting metHb into hemoglobin, such as a deficiency in cytochrome B5 reductase, G6Pd deficiency (mostly in infants), hemoglobin M disease, and pyruvate kinase deficiency. All of those diseases in one way or another effect the red blood cells and prevent normal mechanisms that breakdown methbb, and most involve anemia, jaundice, and/ or neonates.
Exposure to some chemicals may cause it to increase, such as arsine and amines, chlorobenzine (pesticides), chromate (chemical that protects metals from coroding and to improve paint adhesion, nitrite (used to cure meat because it prevents bacterial growth), nitrates (biproduct of septic systems and waste product from certain factories that can increase nitrate levels of fish near land). Some say this is one reason kids under 2 should not eat certain fish and water critters.
MetHb can also be increased by certain drugs, such as nitrates, nitrites, nitroglycerine, nitroprusside, quinomes, sulfonamides, dapsome (Leprocy tx), and chloeoquin (malaria tx).
greater than 10 = bluish coloring around lips and other mucus membranes
greater than 20= anxiety, headache and dyspnea
greater than 30= fatigue, confusion, headache, palps
greater than 50= coma, ceizure, arrhythmia, acidosis
greater than 70 = death
Note: While I'm confident this information is accurate based on my past studies, we'll take it with a grain of salt. I'm saying this because the only source I could find with information regarding this question was Wikepedia.