Verification of pleural fluid pH on radiometer ABL 90 flex plus blood gas analyzer

Pleural fluid pH analysis was verified on three new ABL90 Flex Plus blood gas analyzers (M/S Radiometer, Canada) placed at the primary site of St. Clare's Mercy Hospital.

To verify precision of the assay, buffered pleural fluid samples of pH 6.8, 7.0 and 7.8 were measured in triplicate for 5 days. Linearity and method comparison between ABL 90 and Orion Pro Star PH211 pH meter (Thermo Fisher) were evaluated using buffered samples at each pH level ranging from 6.8 to 7.8. Method comparison was also done using unmodified patient fluid samples (n = 31) analyzed on three blood gas analyzers and Cole-Parmer PHR-146 Micro-Combination pH Electrode meter. The stability of the assay was verified for 120 min and 7 days at room temperature and at -80℃, respectively, using buffered samples. Impacts of fluid matrix on Orion and ABL90 were studied using aqueous buffered samples and buffered patient fluid samples.

Precision shows a small variation in assay results. The assay was linear over pH 6.8 to 7.8. Stability studies indicated very small change at both ambient temperature and at -80℃. Good correlation was found between ABL90 blood gas analyzers and laboratory pH meters with unmodified patient samples and buffered pleural fluid samples of different pHs including medical decision limit of pH 7.3. The substantial bias observed between ABL90, and Orion pH measurements is attributed to sample matrix effect on measurement systems.

The ABL90 analyzer is an acceptable device for measuring pleural fluid pH with short turnaround time. Multiple approaches are required to assure reliability of test results when a reference method is not available, and the analyte level is unstable under normal laboratory conditions.