Point-of-care glucose analysis in neonates using modified quinoprotein glucose dehydrogenase.

BACKGROUND: Asymptomatic hypoglycemia in neonates may contribute to neurologic deficits during development. Whole-blood glucose sensors are often imprecise and inaccurate at the low glucose concentrations found in neonates. SUBJECTS AND METHODS: In this study, a glucose sensor using a mutated glucose dehydrogenase that does not cross-react significantly with maltose was evaluated at three pediatric centers. Blood samples (n=575) from infants less than 30 days of age (hematocrit 23-70%) were analyzed using six reagent lots on three ACCU-CHEK(®) meters (Roche Diagnostics, Indianapolis, IN): the Inform II, Performa, and Aviva. Reference glucose level was determined in duplicate in perchloric acid extracts using a coupled hexokinase procedure. RESULTS: Imprecision of glucose measurement using stable control materials ranged from 2.0% to 3.1% (coefficient of variation) using the glucose meters and from 0.8% to 5.3% (coefficient of variation) in perchloric acid-treated controls. The difference between meter glucose values and reference values showed a slight dependence on hematocrit from 23% to 70% (r=-0.391, P<0.001) but not in the typical range of neonatal hematocrit from 45% to 70% (r=-0.036, P=0.239). Linear regression of the aggregated results yielded the following relationship: Meter glucose=0.99×Reference Glucose+0.04; r(2)=0.976; Syx=0.249. Receiver-operator characteristic analysis of the data using 2.2 mmol/L as the reference threshold for hypoglycemia yielded an area under the curve value of 0.993. All infants with a glucose level of <2.2 mmol/L were detected (100% sensitivity) when the meter glucose value was below 2.8 mmol/L. CONCLUSIONS: These data indicate that the modified ACCU-CHEK chemistry may be used effectively in neonatal settings to detect clinically significant hypoglycemia.

Comparison of PFA-100 and bleeding time testing in pediatric patients with suspected hemorrhagic problems.

BACKGROUND: The bleeding time test is difficult to perform, standardize, and interpret in children. In this study the authors evaluated the sensitivity, specificity, and efficiency of the bleeding time test and the PFA-100 in a series of children referred for possible bleeding problems. PATIENTS AND METHODS: Between February 2000 and August 2001 patients aged more than 6 months and less than 18 years of age who were referred to the authors' institution for a hemostatic evaluation were included in the study if residual blood was available for testing on the PFA-100 instrument. Fifty-two children had platelet count, prothrombin time, partial thromboplastin time, bleeding time, and PFA-100 testing performed as well as an evaluation by a hematologist. For PFA-100 testing, 52 patients had Col/Epi measurements; adequate sample remained for Col/ADP testing on 32. Additional testing for diagnostic purposes was at the discretion of the treating physician. RESULTS: Use of the Col/Epi cartridge in the PFA-100 instrument offered 100% sensitivity and 97% specificity for detection of qualitative platelet abnormalities, compared with 37% and 88%, respectively, for bleeding time testing. For pediatric patients with von Willebrand disease, the sensitivity was 100% using the Col/Epi cartridge, compared with 17% for the bleeding time test. The sensitivities for combined qualitative platelet defects and von Willebrand disease using the Col/Epi or Col/ADP cartridges were 100% and 87%, respectively, compared with 37% for the bleeding time test. CONCLUSIONS: The PFA-100 is a more efficient test; it can replace the bleeding time test as a component of the laboratory evaluation of children with a potential bleeding problem.

Accurate direct spectrophotometric bilirubin measurement combined with blood gas analysis.

BACKGROUND: A new total bilirubin (B(T)) method, based on multiple wavelength absorbance measurements, and an algorithm to calculate concentration, were evaluated for accuracy in specimens containing variable amounts of unconjugated bilirubin (B(U)), conjugated bilirubin (B(C)) and delta (protein-bound) bilirubin (B(D)). METHODS: Quantitation of B(U), B(C), and B(T) (with calculation of B(D)) using a Vitros 250 analyzer served as the comparison method. RESULTS: Analysis of neonatal specimens using a preliminary algorithm yielded good overall agreement with the Vitros B(T) method, but there was considerable variation in the agreement for individual specimens. When specimens from adults selected to yield a range of B(C) and B(D) levels were analyzed, the preliminary algorithm underestimated B(T). Refinement of the method in the form of a finalized algorithm resulted in elimination of the negative bias seen with specimens with high B(D) and B(C) levels, and better agreement for individual neonatal specimens. CONCLUSIONS: This new method overcomes the limitations observed in earlier spectrophotometric methods, and provides accurate results in specimens containing a range of bilirubin forms.

Artifícios analíticos nas determinações do hematócrito por analisadores químicos em sangue total / Analytical artifacts in hematocrit measurements by whole-blood chemistry analyzers

Analisadores compactos, apropriados para testes em pacientes à mão, avaliam o hematócrito pela medida da condutividade do sangue não diluído. Nós avaliamos a exatidão do resultado de hematócrito de um determinado analisador (Instrumentation Laboratory BGE Analyzer) em comparação com um automático contador eletrônico de partículas (CEP) e volume de células sedimentadas (VCS) microhematócrito. Quando amostras (n = 34) de pacientes externos e de enfermaria foram analisadas por todos os três métodos, o analisador AEG estava de acordo com os dois hematócritos CEP e VCS (AEG = 1,00 VCS + 0,3%, Sy/x = 1,6% ; AEG = 1,04 CEP + 0,4%, Sy/x = 2,0%), indicando que todos os três métodos têm performances similares na maioria dos pacientes. Entretanto, um paciente com osmolalidade plasmática aumentada mostrou significante decréscimo nos hematócritos AEG e VCS em comparação ao método CEP. As diferenças nas medidas do hematócrito podiam ser reproduzidas pela adição de solutos ao sangue “in vitro” ou pela modificação de osmolalidade plasmática de ratos "in vivo". Amostras de pacientes submetidos a uma cirurgia cardíaca, cujo sangue tinha grandes mudanças na concentração de proteína, mostrou discrepância entre hematócritos pela condutividade e outros métodos; efeitos similares poderiam ser produzidos pelas mudanças na concentração de proteína ou pela adição "in vitro" de polietileno glicol. Nós concluímos que medidas de condutividade fornecem resultados exatos do hematócrito para sujeitos normais fisiologicamente, mas não para alguns pacientes sob cuidado intensivo e pacientes cirúrgicos.