The Serum 14C-Triolein/3H-01eic Acid Assimilation Test for Differential Diagnosis of Maldigestion and Malabsorption

In 125 consecutive patients the measurement of serum radioactivities after simultaneous ingestion of 14C-triolein and 3H-oleic acid was investigated as a test of lipid assimilation. The sum of the 2-h and 4-h concentrations of 14C in serum (se(2 + 4)14C) was most useful as an index of lipid assimilation, and the 2-h serum 3H/14C ratio (se-3H/14C) reflected lipid digestion. Normal values were se(2 + 4)14C ≥ 1.0% of the dose ingested per litre serum and se-3H/14C < 1.3. Se(2 + 4)14C correlated significantly with faecal fat (r = -0.56, P < 0.001) and indicated malassimilation in 26 of the 50 patients with a faecal fat excretion >7 g/day. False-negative values appeared mainly in the patients with moderate steatorrhoea and gastrointestinal anastomoses. Only one false-positive se(2 + 4)14C value was found. Se-3H/14C was abnormal in 24 of the 34 patients with maldigestion with 2 false-positive results. When the results of se(2 + 4)14C and se-3H/14C were combined, the predictive value of the test result 'normal lipid assimilation' was 0.75, that of the test result 'maldigestion' was 0.93, and that of 'malabsorption' 0.71. It is concluded that the serum 14C-triolein/3H-oleic acid assimilation test is convenient and inexpensive and may be useful when quantitative faecal collections are not available.