Use of a 13C-aminopyrine blood test: first clinical impressions

Abstract

The purpose of this study was to collect initial data to determine the potential clinical usefulness of a 13C-aminopyrine demethylation blood test, and whether additional clinical investigation is warranted. Six dogs, initially suspected of having hepatic disease based on their history, physical examination, imaging studies, general laboratory parameters, or any combination of the above, were enrolled in the study. A baseline blood sample was collected, 2 mg/kg 13C-aminopyrine was administered intravenously, and another blood sample was collected 45 min afterwards. Carbon dioxide was extracted from the blood samples and analyzed using fractional mass spectrometry. Results from the 13C-aminopyrine demethylation blood test were compared to clinical data and histologic findings. Intravenous administration of 13C-aminopyrine leads to a decrease in the percent dose of 13C recovered from dogs with histologically confirmed liver disease. Based on our results, a full-scale investigation of the potential clinical usefulness of a 13C-aminopyrine demethylation blood test for assessment of hepatic function in dogs is warranted.

Figure 1. Formula for calculation of percent dose (PCD). Percent dose belemnitella (PDB) is the calcium carbonate standard used. The standard was a limestone fossil of Belemnitella americana from the Cretaceous Pee Dee formation in South Carolina. The standard has been assigned a δ¹³C-value of 0% and the absolute ¹³C/¹²C-ratio (R) has been reported to be 0.0112372. The δ¹³C_sample is the relative difference of the sample to PDB. The ¹³Csample indicates whether the sample is higher or lower than PDB, with a negative indicating that the sample is lower than PDB. The fractional abundance (F) is useful in isotopic mass calculations. Atom % is also used and is the expression of the isotopic enrichment in samples highly enriched with ¹³C. Atom % excess (APE), which is used in these calculations, is the enrichment level of a sample following administration of a ¹³C tracer in excess of the ¹³C background or baseline level prior to administration of the tracer. These values were used to calculate both mmol excess ¹³C in dose and μmol excess ¹³C/min. The PCD is calculated directly from these 2 values, as indicated in the formula for PCD (24).