Establishing quality indicators for point of care glucose testing: recommendations from the Canadian Society for Clinical Chemists Point of Care Testing and Quality Indicators Special Interest Groups.

OBJECTIVES: Monitoring quality indicators (QIs) is an important part of laboratory quality assurance (QA). Here, the Canadian Society of Clinical Chemists (CSCC) Point of Care Testing (POCT) and QI Special Interest Groups describe a process for establishing and monitoring QIs for POCT glucose testing. METHODS: Key, error prone steps in the POCT glucose testing process were collaboratively mapped out, followed by risk assessment for each step. Steps with the highest risk and ability to detect a non-conformance were chosen for follow-up. These were positive patient identification (PPID) and repeat of critically high glucose measurements. Participating sites were asked to submit aggregate data for these indicators from their site(s) for a one-month period. The PPID QI was also included as part of a national QI monitoring program for which fifty-seven sites submitted data. RESULTS: The percentage of POCT glucose tests performed without valid PPID ranged from 0-87%. Sites without Admission-Discharge-Transfer (ADT) connectivity to POCT meters were among those with the highest percentage of POCT glucose tests performed without valid PPID. The percentage repeated critically high glucose measurements ranged from 0-50%, indicating low compliance with this recommendation. A high rate of discordance was also noted when critically high POCT glucose measurements were repeated, demonstrating the importance of repeat testing prior to insulin administration. CONCLUSIONS: Here, a process for establishing these QIs is described, with preliminary data for two QIs chosen from this process. The findings demonstrate the importance of QIs for identification and comparative performance monitoring of non-conformances to improve POCT quality.

Correlation of cord blood pH, base excess, and lactate concentration measured with a portable device for identifying fetal acidosis.

OBJECTIVE: To determine the effectiveness of portable lactate analyzers in identifying fetal acidosis by correlating arterial and venous lactate values from umbilical cord blood with lactate, pH, and base excess measurements from central laboratory analyzers. METHODS: We performed a prospective study using arterial and venous cord blood from 52 women with a singleton fetus delivered at term. We evaluated the correlation between the cord blood lactate concentration measured using two of the same portable devices (Lactate Plus, Nova Biomedical) with the result from a central laboratory analyzer. Analyses of the correlation between arterial lactate concentration measured on the portable device with arterial pH and base excess were then performed. RESULTS: We observed a median arterial pH of 7.24 (range 7.05 to 7.35) and a median arterial lactate concentration of 3.7 mmol/L (range 1.7 to 8.8 mmol/L). An excellent correlation was observed between lactate concentrations measured by the two portable devices (arterial R² = 0.98 and venous R² = 0.98), and between the portable device and the central laboratory analyzer (arterial R² = 0.94 and venous R² = 0.95). In our population, the optimal cut-offs to predict a pH < 7.20 or a base excess > -8.0 mmol/L were a lactate concentration of 4.9 mmol/L and 5.3 mmol/L, respectively, according to receiver operator characteristic analysis. With a lactate concentration > 4.9 mmol/L, the portable device had a sensitivity of 82% and a specificity of 90% to identify samples with an arterial pH < 7.20. CONCLUSION: Cord blood lactate concentration measured with a portable device is a good predictor of cord blood base excess and pH. Future studies should be designed to correlate scalp blood lactate measurements with clinical outcomes.

Objectif : Déterminer l'efficacité des analyseurs de lactate portatifs, pour ce qui est de l'identification de l'acidose fœtale, en mettant en corrélation les valeurs artérielle et veineuse du lactate constatées dans le sang de cordon ombilical et les mesures du lactate, du pH et de l'excès de bases révélées par les analyseurs du laboratoire central. Méthodes : Nous avons mené une étude prospective en utilisant le sang de cordon artériel et veineux prélevé chez 52 femmes qui ont connu une grossesse monofœtale s'étant soldée en un accouchement à terme. Nous avons évalué la corrélation entre la concentration en lactate du sang de cordon mesurée au moyen de deux exemplaires du même appareil portatif (Lactate Plus, Nova Biomedical) et le résultat obtenu au moyen d'un analyseur du laboratoire central. Nous avons par la suite procédé à des analyses de la corrélation entre la concentration artérielle en lactate mesurée au moyen de l'appareil portatif et les valeurs artérielles du pH et de l'excès de bases. Résultats : Nous avons constaté un pH artériel médian de 7,24 (plage : 7,05 - 7,35) et une concentration artérielle en lactate médiane de 3,7 mmol/l (plage : 1,7 - 8,8 mmol/l). Une excellente corrélation a été constatée entre les concentrations en lactate mesurées par les deux appareils portatifs (R2 artériel = 0,98 et R2 veineux = 0,98) et entre les concentrations mesurées par l'appareil portatif et par l'analyseur du laboratoire central (R2 artériel = 0,94 et R2 veineux = 0,95). Au sein de notre population, les seuils optimaux permettant de prédire un pH < 7,20 ou un excès de bases > −8,0 mmol/l ont été des concentrations en lactate de 4,9 mmol/l et de 5,3 mmol/l, respectivement, selon l'analyse de la fonction d'efficacité du récepteur. En présence d'une concentration en lactate > 4,9 mmol/l, l'appareil portatif comptait une sensibilité de 82 % et une spécificité de 90 % pour ce qui est de l'identification des prélèvements présentant un pH artériel < 7,20. Conclusion : La concentration en lactate du sang de cordon qui est mesurée au moyen d'un appareil portatif constitue un bon facteur prédictif pour ce qui est du pH et de l'excès de bases du sang de cordon. De futures études devraient être conçues de façon à pouvoir mettre en corrélation les concentrations en lactate dans le sang prélevé sur le cuir chevelu et les résultats cliniques.

Membrane-type 1 matrix metalloproteinase stimulates cell migration through epidermal growth factor receptor transactivation.

Proteolysis of extracellular matrix proteins by membrane-type 1 matrix metalloproteinase (MT1-MMP) plays a pivotal role in tumor and endothelial cell migration. In addition to its proteolytic activity, several studies indicate that the proinvasive properties of MT1-MMP also involve its short cytoplasmic domain, but the specific mechanisms mediating this function have yet to be fully elucidated. Having previously shown that the serum factor sphingosine 1-phosphate stimulates MT1-MMP promigratory function through a process that involves its cytoplasmic domain, we now extend these findings to show that this cooperative interaction is permissive to cellular migration through MT1-MMP-dependent transactivation of the epidermal growth factor receptor (EGFR). In the presence of sphingosine 1-phosphate, MT1-MMP stimulates EGFR transactivation through a process that is dependent upon the cytoplasmic domain of the enzyme but not its catalytic activity. The MT1-MMP-induced EGFR transactivation also involves G(i) protein signaling and Src activities and leads to enhanced cellular migration through downstream extracellular signal-regulated kinase activation. The present study, thus, elucidates a novel role of MT1-MMP in signaling events mediating EGFR transactivation and provides the first evidence of a crucial role of this receptor activity in MT1-MMP promigratory function. Taken together, our results suggest that the inhibition of EGFR may represent a novel target to inhibit MT1-MMP-dependent processes associated with tumor cell invasion and angiogenesis.

Regulation of vascular endothelial growth factor receptor-2 activity by caveolin-1 and plasma membrane cholesterol.

The stimulation of vascular endothelial growth factor receptor-2 (VEGFR-2) by tumor-derived VEGF represents a key event in the initiation of angiogenesis. In this work, we report that VEGFR-2 is localized in endothelial caveolae, associated with caveolin-1, and that this complex is rapidly dissociated upon stimulation with VEGF. The kinetics of caveolin-1 dissociation correlated with those of VEGF-dependent VEGFR-2 tyrosine phosphorylation, suggesting that caveolin-1 acts as a negative regulator of VEGF R-2 activity. Interestingly, we observed that in an overexpression system in which VEGFR-2 is constitutively active, caveolin-1 overexpression inhibits VEGFR-2 activity but allows VEGFR-2 to undergo VEGF-dependent activation, suggesting that caveolin-1 can confer ligand dependency to a receptor system. Removal of caveolin and VEGFR-2 from caveolae by cholesterol depletion resulted in an increase in both basal and VEGF-induced phosphorylation of VEGFR-2, but led to the inhibition of VEGF-induced ERK activation and endothelial cell migration, suggesting that localization of VEGFR-2 to these domains is crucial for VEGF-mediated signaling. Dissociation of the VEGFR-2/caveolin-1 complex by VEGF or cyclodextrin led to a PP2-sensitive phosphorylation of caveolin-1 on tyrosine 14, suggesting the participation of Src family kinases in this process. Overall, these results suggest that caveolin-1 plays multiple roles in the VEGF-induced signaling cascade.

Combined inhibition of PDGF and VEGF receptors by ellagic acid, a dietary-derived phenolic compound.

The vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptors play essential and complementary roles in angiogenesis and combined inhibition of these receptors has been shown to result in potent antitumor activity in vivo. In this study, we report that ellagic acid (EA), a natural polyphenol found in fruits and nuts, inhibits VEGF-induced phosphorylation of VEGFR-2 in endothelial cell (EC) as well as PDGF-induced phosphorylation of PDGFR in smooth muscle cells, leading to the inhibition of downstream signaling triggered by these receptors. EA also specifically inhibited VEGF-induced migration of ECs as well as their differentiation into capillary-like tubular structures and abolished PDGF-dependent smooth muscle cell migration. Interestingly, EA presents a greater selectivity for normal cells than for tumor cells since the migration of the U87 and HT1080 cell lines were much less affected by this molecule. The identification of EA as a naturally occurring dual inhibitor of VEGF and PDGF receptors suggests that this molecule possesses important antiangiogenic properties that may be helpful for the prevention and treatment of cancer.

Src-mediated tyrosine phosphorylation of caveolin-1 induces its association with membrane type 1 matrix metalloproteinase.

We have recently shown that stimulation of endothelial cells with vascular endothelial growth factor (VEGF) induces dissociation of caveolin-1 from the VEGFR-2 receptor, followed by Src family kinase-dependent tyrosine phosphorylation of the protein (Labrecque, L., Royal, I., Surprenant, D. S., Patterson, C., Gingras, D., and Beliveau, R. (2003) Mol. Biol. Cell 14, 334-347). In this study, we provide evidence that the VEGF-dependent tyrosine phosphorylation of caveolin-1 induces interaction of the protein with the membrane-type 1 matrix metalloproteinase (MT1-MMP). This interaction requires the phosphorylation of caveolin-1 on tyrosine 14 by members of the Src family of protein kinases, such as Src and Fyn, because it is completely abolished by expression of a catalytically inactive Src mutant or by site-directed mutagenesis of tyrosine 14 of caveolin-1. Most interestingly, the association of MT1-MMP with phosphorylated caveolin-1 induced the recruitment of Src and a concomitant inhibition of the kinase activity of the enzyme, suggesting that this complex may be involved in the negative regulation of Src activity. The association of MT1-MMP with phosphorylated caveolin-1 occurs in caveolae membranes and involves the cytoplasmic domain of MT1-MMP because it was markedly reduced by mutation of Cys574 and Val582 residues of the cytoplasmic tail of the enzyme. Most interestingly, the reduction of the interaction between MT1-MMP and caveolin-1 by using these mutants also decreases MT1-MMP-dependent cell locomotion. Overall these results indicate that MT1-MMP associates with tyrosine-phosphorylated caveolin-1 and that this complex may play an important role in MT1-MMP regulation and function.