The role of urinary fractionated metanephrines in the diagnosis of phaeochromocytoma.

BACKGROUND & OBJECTIVES: Plasma and urinary metanephrines are used as screening tests for the diagnosis of phaeochromocytoma. The recommended cut-off levels are not standardized. This study was conducted to identify a cut-off level for 24 h urinary fractionated metanephrines viz. metanephrine (uMN) and normetanephrine (uNMN) using enzyme immunoassay for the diagnosis of phaeochromocytoma. METHODS: Consecutive patients suspected to have phaeochromocytoma were included in the study. uMN and uNMN in 24 h urinary sample were measured using a commercial ELISA kit. RESULTS: Overall, 72 patients were included over a period of 18 months. Twenty patients had histopathologically confirmed phaeochromocytoma and in 52 patients phaeochromocytoma was ruled out. Using the upper limit of normal stated by the assay manufacturer as the cut-off, uMN >350 µg/day had a low sensitivity and uNMN >600 µg/day had a poor specificity. By increasing the cut-off value of uNMN to twice the upper limit, specificity increased significantly without much loss in sensitivity. Combining uMN and uNMN using a cut-off twice the upper limit improved the diagnostic performance - sensitivity (95%); specificity (92.3%); positive predictive value (PPV - 82.6%); negative predictive value (NPV - 98%). In subsets of patients with a variable pretest probability for phaeochromocytoma, the PPV correlates well with the occurred of these tumors decreased, while the NPV remained at 100 per cent. INTERPRETATION & CONCLUSIONS: ELISA is a simple and reliable method for measuring uMN and uNMN. The test has a good NPV and can be used as an initial screening test for ruling out phaeochromocytoma. Each hospital will have to define the cut-off value for the assay being used, choosing a proper control population.

Agreement between paired blood gas values in samples transported either by a pneumatic system or by human courier.

BACKGROUND: Rapid accurate assessment of metabolic derangements is crucial in the critically ill. We evaluated if arterial blood gas (ABG) samples transported through a pneumatic tube system (PTS) agreed with values transported by a human courier. METHODS: In this prospective study of 50-paired ABG samples, the couriered reference ABG was compared with those transported by PTS. Agreement was summarised by the mean difference with 95% limits of agreement (LOA) and Lin's concordance correlation (pc). RESULTS: The mean (±SD) time from sampling to analysis was 35.7±23.2 (courier) and 38.6±22.1 (PTS) minutes. Agreement was good between courier and PTS for pH, PaCO(2), bicarbonate, oxygen saturation and PaO(2) values (pc>0.97). Although the mean difference in PaO(2) values between PTS and courier was small (-0.9 mm Hg) and the agreement was good, individual differences were clinically significant (95% LOA -40.8 to 39.0). For PaO(2) <160 mm Hg, analysis of PTS samples yielded erroneously high PaO(2) values and vice versa for PaO(2)>160 mm Hg compared to manual courier. This suggested exaggerated oxygen movement between the blood sample and air in the PTS. CONCLUSIONS: In this study, analysis of samples transported through the PTS resulted in clinically unacceptable PaO(2) values. Delay in transport and analysis of ABG samples should be avoided and samples transported manually if they cannot be assessed on-site.