Estimation of 14C-triolein assimilation as a test of lipid assimilation. Breath test or measurement of serum radioactivity?

Two tests of lipid assimilation based on estimation of 14C-triolein assimilation from expiratory 14CO2 (breath test) and from serum radioactivity of 14C, respectively, were investigated in 48 consecutive patients suspected of having malassimilation. Patients with proven malassimilation had significantly lower expiration of 14CO2 and lower serum radioactivity of 14C than patients with normal lipid assimilation. The se-14C test correctly diagnosed significantly more patients with malassimilation than the breath test; the diagnostic efficiencies were 0.87 and 0.74, respectively. The results of both tests correlated with measurement of faecal fat. However, within the group of patients with proven malassimilation the results of the breath test correlated poorly with faecal fat, whereas a significant correlation was found between the se-14C test and faecal fat within this group. Correspondingly, the correlation between the results of the breath test and the se-14C test was poor, indicating that intermediate metabolism influences the results.