The potential clinical utility of serum alpha-protryptase levels

Because biopsy criteria for diagnosing systemic mastocytosis are not precise, the value of serum alpha-protryptase levels in the work-up of suspected systemic mastocytosis should be considered.

A retrospective analysis was performed on subjects with total tryptase serum levels that were high (>/=20 ng/mL), while beta-tryptase serum levels were normal (<1 ng/mL) or modestly elevated (1 to 5 ng/mL).

Over a 3.5-year period, 52 qualifying specimens were identified from 1369 consecutive samples. The corresponding subjects were divided into those with suspected mastocytosis and those with suspected anaphylaxis. Subjects with suspected mastocytosis were subdivided into 3 subgroups on the basis of biopsy results (positive, negative, or not available). Subjects with suspected anaphylaxis were subdivided into living and deceased subgroups.

Among the 15 subjects who underwent biopsy, alpha-protryptase serum levels (the difference between directly-measured levels of serum total tryptase and beta-tryptase), when greater than 75 ng/mL (n = 9), were always associated with a positive biopsy result for systemic mastocytosis; levels from 20 to 75 ng/mL (n = 6) were associated with a positive biopsy result in 50% of subjects. alpha-Protryptase serum levels may be a more sensitive screening test than a bone marrow biopsy for this disorder. Also, elevated alpha-protryptase serum levels in some adult patients return to normal over time, suggesting that mast cell hyperplasia resolved in these patients. Finally, a high alpha-protryptase level may reveal anaphylaxis to be a presenting manifestation of systemic mastocytosis or mast cell hyperplasia.

Levels of serum alpha-protryptase, relative to those of beta-tryptase, appear to be useful in the diagnostic work-up and follow-up of subjects with suspected systemic mastocytosis.