Estimating the within‐subject (CV(I)) and between‐subject (CV(G)) biological variation of serum tryptase

BACKGROUND: Tryptase is used as a biomarker to support the diagnosis of anaphylaxis and hematologic diseases. In the event of a mast cell activation during anaphylaxis, a temporary increase in the concentration of tryptase may be seen. On the basis of clinical studies, an increase of 2 µg/L + 20% from basis level has been proposed as significant. To evaluate the increase in tryptase levels, the within‐subject (CV(I)) and between‐subject (CV(G)) biological variations should be known. This study was conducted to estimate the biological variation of tryptase and to identify the reference change value (RCV). METHODS: Blood samples were collected from healthy volunteers once a week consecutively over a 10‐week period. Tryptase was measured by the use of a fluoroenzyme immunoassay (ImmunoCAP(TM); Thermo Fisher Scientific), and linear mixed‐effects models were used to calculate the biological variation and RCV for both nontransformed and log‐transformed tryptase. RESULTS: Fourteen presumably healthy young adults (six males and eight females, age 23–35 years) were included. The CV(I) was 5.6% and the CV(G) was 31.5% (nontransformed data). Log‐transformed data showed similar results. The analytical variation (CV(A)) was 6.3% and the RCV was 23.5%. CONCLUSIONS: Young healthy adults without ongoing allergic reactions show low within‐subject biological variation. Higher biological variation was observed between subjects.