The normal values for histamine are 0.1 – 1.8ng/ml, and this range is unisex for all age groups.
Significantly elevated histamine and/or tryptase levels in a person with symptoms of anaphylaxis are strong evidence for that diagnosis.
Normal histamine results may indicate that a person’s symptoms are due to another cause, or that the sample was not collected at the right time. With anaphylaxis, blood histamine levels rise rapidly and can fall back to normal within about 30-60 minutes.
If a sample is drawn too late, results may be normal. If a tryptase test is also performed, its value can be compared to the histamine levels.
Tryptase levels rise and fall more slowly than histamine levels, peaking within 1 to 2 hours of symptom development. If the timing of sample collection was appropriate and neither the blood histamine or tryptase concentration is elevated, it is less likely that a person had anaphylaxis.
However, a person can have anaphylaxis or mastocytosis without elevated histamine levels, so the diagnosis cannot be ruled out just because the test is negative. Increased levels of histamine and/or N-methylhistamine in a 24-hour urine sample indicate an event associated with mast cell activation.
Persistently elevated histamine and/or tryptase levels in a person with mastocytosis symptoms make it likely that the person has this condition. The diagnosis must still be confirmed with other testing.