Version July 2025
| Clinical condition | Total tryptase levels (ng/mL or mcg/L) | |
| Normal | BST ≤11.4 | If patients with HaT or patients with kidney failure are excluded, then the upper limit of the normal range is 11.4 ng/mL. |
| Hereditary alpha-tryptasemia (HaT) | BST >8 | For each extra copy of TPSAB1 encoding alpha-tryptase, the BST level increases by 9 to 10 ng/mL. HaT is the most common reason for increased BST levels in those of European ancestry. Most individuals have levels between 8 and 50 ng/mL. If a subject with BST levels 6.5 to 7.9 ng/mL is suspected of having HaT and has a family member with the HaT genotype, then genotyping may be appropriate. |
| Kidney failure | BST >6 | Modest increases in BST levels have been reported, particularly in hemodialysis patients, but rarely exceed 30 ng/mL. Kidney failure is the second most common condition causing an increased BST level. |
| Systemic mastocytosis (SM) | BST >20 | Approximately 70% of SM patients have a BST >20 ng/mL, while a few have levels in the normal range. The prevalence of HaT in SM is 2- to 3-fold higher than in healthy subjects. In patients with both conditions, the BST level needs to be adjusted for the CNV*[1] but cannot be used as a diagnostic criterion when other acquired conditions that raise the BST level are present. |
| Anaphylaxis | Acute serum tryptase¶ ECNM: >1.2 × BST + 2 NIH: >1.685 × BST | A BST level of 4 ng/mL gives an equivalent threshold for each formula. The ECNM one has higher specificity and lower sensitivity at BST levels <4, while the NIH formula has higher specificity and lower sensitivity at BST levels >4. In each case, clinical judgment is needed. |
| Clonal myelocytic disorders (excluding SM) | >10 ng/mL | Examples of disorders include acute myeloid leukemia, myelocytic hypereosinophilic syndrome, myelodysplastic syndrome, and others. Levels uncommonly exceed 50 ng/mL. |
BST: basal serum tryptase; CNV: copy number variant; ECNM: European Competence Network on Mastocytosis; HaT: hereditary alpha-tryptasemia; NIH: National Institutes of Health; TPSAB1: tryptase alpha/beta 1.
* NIH, subtract 9 to 10 ng/mL for each extra TPSAB1 CNV; another proposed algorithm is to divide BST by 1 + the number of CNVs.
¶ An acute serum tryptase level should be collected 30 minutes to 6 hours after onset of signs and symptoms of a possible anaphylaxis episode and optimally 30 minutes to 2 hours after onset and correlates best with the magnitude of hypotension.