A study examining the bias of albumin and albumin/creatinine ratio measurements in urine.

BACKGROUND: The objective of the study was to examine the bias of albumin and albumin/creatinine (ACR) measurements in urine. METHODS: Pools of normal human urine were augmented with purified human serum albumin to generate a series of 12 samples covering the clinical range of interest for the measurement of ACR. Albumin and creatinine concentrations in these samples were analyzed three times on each of 3 days by 24 accredited laboratories in Canada and the USA. Reference values (RV) for albumin measurements were assigned by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) comparative method and gravimetrically. Ten random urine samples (check samples) were analyzed as singlets and albumin and ACR values reported according to the routine practices of each laboratory. RESULTS: Augmented urine pools were shown to be commutable. Gravimetrically assigned target values were corrected for the presence of endogenous albumin using the LC-MS/MS comparative method. There was excellent agreement between the RVs as assigned by these two methods. All laboratory medians demonstrated a negative bias for the measurement of albumin in urine over the concentration range examined. The magnitude of this bias tended to decrease with increasing albumin concentrations. At baseline, only 10% of the patient ACR values met a performance limit of RV ± 15%. This increased to 84% and 86% following post-analytical correction for albumin and creatinine calibration bias, respectively. CONCLUSIONS: International organizations should take a leading role in the standardization of albumin measurements in urine. In the interim, accuracy based urine quality control samples may be used by clinical laboratories for monitoring the accuracy of their urinary albumin measurements.

In utero copper treatment for Menkes disease associated with a severe ATP7A mutation.

Menkes disease is a lethal X-linked recessive neurodegenerative disorder of copper transport caused by mutations in ATP7A, which encodes a copper-transporting ATPase. Early postnatal treatment with copper injections often improves clinical outcomes in affected infants. While Menkes disease newborns appear normal neurologically, analyses of fetal tissues including placenta indicate abnormal copper distribution and suggest a prenatal onset of the metal transport defect. In an affected fetus whose parents found termination unacceptable and who understood the associated risks, we began in utero copper histidine treatment at 31.5 weeks gestational age. Copper histidine (900 µg per dose) was administered directly to the fetus by intramuscular injection (fetal quadriceps or gluteus) under ultrasound guidance. Percutaneous umbilical blood sampling enabled serial measurement of fetal copper and ceruloplasmin levels that were used to guide therapy over a four-week period. Fetal copper levels rose from 17 µg/dL prior to treatment to 45 µg/dL, and ceruloplasmin levels from 39 mg/L to 122 mg/L. After pulmonary maturity was confirmed biochemically, the baby was delivered at 35.5 weeks and daily copper histidine therapy (250 µg sc b.i.d.) was begun. Despite this very early intervention with copper, the infant showed hypotonia, developmental delay, and electroencephalographic abnormalities and died of respiratory failure at 5.5 months of age. The patient's ATP7A mutation (Q724H), which severely disrupted mRNA splicing, resulted in complete absence of ATP7A protein on Western blots. These investigations suggest that prenatally initiated copper replacement is inadequate to correct Menkes disease caused by severe loss-of-function mutations, and that postnatal ATP7A gene addition represents a rational approach in such circumstances.

Performance of StatSensor Point-of-Care Device for Measuring Creatinine in Patients With Chronic Kidney Disease and Postkidney Transplantation.

BACKGROUND: The StatSensor is a point-of-care device which measures creatinine in capillary whole blood. Previous studies reported an underestimation of the creatinine measurements at high creatinine concentrations and were performed in the prestandardization era for creatinine. OBJECTIVE: This accuracy-based study evaluates the use of this device in kidney-transplanted patients and those with chronic kidney disease (CKD). DESIGN: Cross-sectional diagnostic accuracy study. SETTING: Nephrology outpatient clinic in an urban tertiary center. PARTICIPANTS: Adults with CKD or a functioning kidney transplant. MEASUREMENTS: Duplicate StatSensor creatinine measurements were performed on capillary whole blood samples collected by direct fingerstick and SAFE-T-FILL collection device. Results were compared with simultaneous venous blood sampling for serum and plasma creatinine measured by an enzymatic method on the Roche Integra 400 mainframe analyzer with traceability to the ID-GC-MS (isotope dilution gas chromatography mass spectrometry) reference method. METHODS: Deming regression, Pearson correlation coefficient, and Bland-Altman analysis were used to assess accuracy and comparability between capillary whole blood measured by StatSensor and plasma creatinine measured by routine analyzer with traceability to the reference method. Estimated glomerular filtration (eGFR) rates were calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and concordance with Kidney Disease Improving Global Outcomes (KDIGO) CKD stage classification was evaluated. RESULTS: There were 60 participants (mean age = 61.9 ± 15.0 years, 55% men, 33% transplant, mean plasma creatinine = 137 ± 59 µmol/L). Bland-Altman analysis indicated a positive mean bias of 12.7 µmol/L between StatSensor fingerstick creatinine measurement and plasma creatinine. Comparison of eGFR (CKD-EPI) calculated from the StatSensor fingerstick creatinine versus plasma creatinine showed misclassification across all KDIGO CKD stages. Postanalytical correction of the bias did not improve misclassifications. The use of mean of duplicate StatSensor creatinine results did not improve performance compared with the use of singlet results. LIMITATIONS: Single center, limited participant numbers. CONCLUSIONS: The results of our study suggest that the limiting characteristics of the StatSensor device are not only bias, but also imprecision. The level of imprecision observed may influence clinical decision-making and limit the usefulness of StatSensor as a CKD screening tool. If choosing to utilize it for either screening for or monitoring CKD, it is essential that clinicians understand the limitations of point-of-care devices and apply this knowledge to test interpretation.

CONTEXTE: Le StatSensor est un appareil portatif conçu pour mesurer le taux de créatinine dans le sang capillaire total. Des études antérieures, réalisées avant la standardisation des mesures de la créatinine, ont rapporté une sous-estimation des mesures à des concentrations élevées. OBJECTIF: Cette étude centrée sur la précision a examiné l'utilisation de cet appareil chez des patients transplantés d'un rein et des patients atteints d'insuffisance rénale chronique (IRC). TYPE D'ÉTUDE: Étude transversale centrée sur la précision du diagnostic. CADRE: La clinique ambulatoire de néphrologie d'un centre de soins tertiaires en milieu urbain. SUJETS: Des adultes atteints d'IRC ou transplantés avec un rein fonctionnel. MESURES: Les mesures de créatinine par StatSensor ont été effectuées en double sur des échantillons de sang capillaire total prélevés par ponction digitale directe et à l'aide du dispositif de prélèvement SAFE-T-FILL. Ces résultats ont été comparés à un prélèvement veineux simultané pour la mesure des taux de créatinine sérique et plasmatique par la méthode enzymatique avec l'analyseur Integra 400 de Roche avec traçabilité à la méthode de référence ID-GC-MS. MÉTHODOLOGIE: La régression de Deming, le coefficient de corrélation de Pearson et l'analyse de Bland-Altman ont été utilisés pour évaluer la précision et la comparabilité entre les mesures du sang capillaire total par StatSensor et la mesure de créatinine plasmatique obtenue par l'analyseur de routine avec traçabilité à la méthode de référence. Le débit de filtration glomérulaire estimé (DFGe) a été calculé avec l'équation CKD-EPI, puis la concordance avec la classification des stades KDIGO pour l'IRC a été évaluée. RÉSULTATS: L'étude a inclus 60 patients (55 % d'hommes; âge moyen 61,9 ± 15,0 ans) dont 33 % étaient transplantés. Le taux moyen de créatinine plasmatique s'établissait à 137 ± 59 µmol/L. L'analyse de Bland-Altman indique un biais positif moyen de 12,7 µmol/L entre la mesure de créatinine obtenue avec StatSensor par ponction digitale et le taux de créatinine plasmatique. La comparaison entre le DFGe (CKD-EPI) calculé à partir des mesures obtenues par ponction digitale avec StatSensor et de la mesure de créatinine plasmatique a montré une classification erronée à tous les stades KDIGO pour l'IRC. La correction du biais après l'analyse n'a pas amélioré les erreurs de classification. L'utilisation de la moyenne des résultats obtenus par StatSensor sur les échantillons prélevés en double n'a pas amélioré les performances par rapport à l'utilisation de singulets. LIMITES: Étude monocentrique, nombre de participants limité. CONCLUSION: Nos résultats suggèrent que les caractéristiques de limitation du StatSensor ne constituent pas qu'un biais, mais également une imprécision. Ce degré d'imprécision peut influencer la prise de décision clinique et limiter l'utilité du StatSensor comme outil de dépistage de l'IRC. Il est essentiel que les cliniciens soient conscients des limites de ces dispositifs et qu'ils appliquent ces connaissances à l'interprétation des résultats s'ils choisissent de les utiliser pour dépister ou surveiller l'IRC. ENREGISTREMENT DE L'ESSAI: Sans objet, il ne s'agissait pas d'un essai clinique.