The numbers in the diagram are generally accepted as typical – they are guidelines only. Some laboratories always seem to test high and some low. The red line is widely accepted as showing the level below which the lungs are not adequately protected.
There are two scales commonly used:
- the conventional units — milligrams per decilitre — mg/dL
- SI units (International Standard) — micro-moles per litre — μmol/L
If you are given an AAT level in conventional units then multiply by 0.184 to get the level in SI units. To go from SI units to conventional units then divide by 0.184 (or multiply by 5.34 which is the same thing).
Researchers tend to use the SI units. Clinicians tend to use conventional units.
Occasionally you may come across variations on the conventional scale: grams, centilitres, etc. Simply multiply or divide by powers of 10 to convert to mg/dL. For example, 0.6 g/L (grams per litre) is 600 milligrams per litre or 60 milligrams per decilitre. Using the conversion factor given above (0.184), 60 mg/dL is a fraction over 11 μmol/L – just below the red line. This could point to SZ or, just possibly, MZ. This issue could be resolved by phenotyping or genotyping the person concerned. Another possible option would be to test close family members.
The reason for the wide range of values for a given phenotype – especially for MM and MS is that the body produces extra AAT when it detects an infection or a major irritation of the lungs.