Preliminary assessment of glycine conjugation of para-aminobenzoic acid as a quantitative test of liver function

Our hypothesis is that because of its hepatic metabolism paraaminobenzoic acid (PABA) could be a test of liver function. PABa is well absorbed by the gastrointestinal tract and acetylated and conjugated in the liver to glycine before being excreted. Its three major metabolites include para-acetoamidobenzoic acid (PAABA), paraaminohippuric acid (PAHA), and paraacetamidohippuric acid (PAAHA). In this study, we measured the metabolism of lidocaine to monoethylglycinexylidide (MEGX) and PABA to PAHA + PAAHA/PABA + PAABA + PAHA + PAAHA (hippurate ratio) in 14 patients with liver disease and 12 control subjects. Comparison of the total bilirubin with the hippurate ratio (at 30 min) and the conventional MEGX test (at 15 min) was assessed. The 30 min hippurate ratio correlated well with the 15 min MEGX results ( r = 0.69). While these results are preliminary the PABA test appears to be equally sensitive to MEGX and has the distinct advantage over the MEGX test of being administered orally versus the intravenous administration of lidocaine which is often associated with unwanted side-effects such as hypotension, drowsiness and paresthesias.