Photo-cross-linked decyl methacrylate films for electrochemical and optical polyion probes.

Potentiometric and optical polyion probes based on photo-cross-linked thin films of decyl methacrylate (DMA) are described, and the effects of film composition on the response toward heparin are examined in detail. In accordance with existing theory governing potentiometric polyion response, lowering the amounts of plasticizer and tridodecylmethylammonium chloride ion exchanger within the film enhances its sensitivity toward heparin. Varying the cross-linker content of a DMA-based film, however, provides an additional mechanism to regulate its physical structure and, hence, the observed potentiometric polyion response. Films with low hexanedioldimethacrylate cross-linker content yield optimal potentiometric heparin detection limits (0.04 microM), suggesting a lower diffusion coefficient within such films, apparently due to interactions between adjacent pendant decyl groups. Increasing crosslinker content interrupts these interactions and facilitates diffusion. This knowledge is applied to optimize optical heparin sensing via DMA films covalently attached to glass substrates. When used in a limited volume/fixed exposure time measurement mode, such optically sensitive films can detect clinically relevant levels of heparin (0.5-5 units/mL) in undiluted human plasma.

Bone lead concentrations assessed by in vivo X-ray fluorescence.

The assessment of past chronic lead exposure is difficult. Chronic lead burden is not always correctly assessed using laboratory-based tests that are useful for acute or recent exposures. We describe a case of suspected chronic lead exposure that illustrated the need for improved and possibly noninvasive methods to determine cumulative lead body burden. X-Ray fluorescence (XRF) is discussed as a method to obtain in vivo bone lead measurements. We discuss the potential of such measurements as accurate biomarkers of cumulative exposure and whether XRF can be used for retroactive exposure assessment or to predict risk of future health problems.

Evaluation of the TAS analyzer and the low-range heparin management test in patients undergoing extracorporeal membrane oxygenation.

BACKGROUND: The new Low-Range Heparin Management Test (LHMT), a method for point-of-care testing (POCT) of heparinization, has been designed to function at the low to moderate heparin concentrations typically found in patients undergoing extracorporeal membrane oxygenation (ECMO). In this study, the new method is compared with two POCT methods and a laboratory-based anti-Xa assay. METHODS: We obtained 760 whole blood samples from 13 patients undergoing ECMO. All samples were tested immediately by the LHMT, the Activated Clotting Time (ACT) test, and its low-range counterpart (ACT-LR). Aliquots from the same blood draw were frozen for later anti-Xa analysis using the Diagnostica Stago method on the Roche Cobas Fara-II. RESULTS: The precision was best for duplicate citrated LHMT samples (CV = 3.1%). LHMT clotting times (overall median, 162 s) were typically shorter than ACT or ACT-LR times (247 and 235 s, respectively). The relationship between the LHMT and the other POCT methods differed significantly from patient to patient (P <0.0001), and a meaningful single relationship between the methods could not be obtained. The overall correlation coefficient between clotting time values and actual heparin concentrations was < or = 0.48 for each of the instruments tested, although time plots of each analyzer's data suggested that they detected heparin dosage changes within single patients. CONCLUSIONS: The performance of the LHMT on the TAS Analyzer is equivalent to that of currently commercially available POCT methods. The lack of agreement between absolute clotting time values and heparin concentrations suggests the need for reexamination of current ECMO patient management strategy.