Biological variance of cholinesterase and 5'-nucleotidase in serum of healthy persons.

We measured cholinesterase (EC 3.1.1.8) and 5'-nucleotidase (EC 3.1.3.5) activities in serum of 24 healthy laboratory staff during 12 months. Overall mean activities ranged from 5.3 to 13.4 kU/L for cholinesterase and 5.4 to 9.8 U/L for 5'-nucleotidase. Cholinesterase activity was significantly (p less than 0.01) higher for men than for women. 5'-Nucleotidase activity was significantly (p = 0.01) higher for subjects 40 years or older than for those younger than 40, but was not different with respect to sex or time of year. Average intra- and interindividual variances (SD2) were 0.38 and 2.69 for cholinesterase and 1.41 and 0.97 for 5'-nucleotidase, respectively. Intra- to interindividual standard deviation ratios were 0.38 for cholinesterase and 1.21 for 5'-nucleotidase. Average within-run analytical variances were 0.13 and 0.3 (4% and 13% of total variance) for cholinesterase and 5'-nucleotidase, respectively. The importance of these findings in regards to diagnostic interpretation of serum cholinesterase and 5'-nucleotidase results is discussed.