ABSTRACT
Objective To evaluate the matrix effects in serum urea measurements of external quality assessment(EQA)materials and commercial reference materials(calibrators or controls)on enzymatic methods and to verify the trueness of the enzymatic methods.Methods The Clinical and Laboratory Stadards Institute(CLSI)EP 14-A2 protocol was used for the evaluation of matrix effect.An isotope dilution gas chromatography mass spectrometry method was used as the comparative method.Twenty five fresh patient serum samples,15 EQA materials and 13 calibrators or controls were analyzed with 7 enzymatic methods (evaluated methods)and the comparative method and results were processed according to the protocol. The trueness of the evaluated methods were also assessed by comparing the fresh sample results obtained with the evaluated and comparative methods.Results Eight of 15 EQA materials and 3 of 13 calibrators or controls showed no matrix effects on all the 7 routine methods.One processed sample showed matrix effect on all the routine methods.Method dependent matrix effects of other materials were observed on other materials.Calibration biases were also observed on some enzymatic methods.Conclusions Matrix effects and calibration bias have been observed in serum urea measurements.Continued efforts are needed for improving the accuracy and the comparability of serum urea measurements.
ABSTRACT
Objectivo To analyze urine organic acids in the urine using gas chromatography-mass spectrometry(GC/MS)for diagnosis of inherited metabolic diseases,especially for organic acids metabolic disorders.Methods 195 clinical urine samples from the patients with suspected organic acids metabolic disorders and 5 normal urine from adults were collected.After mixing some urine with intemal standards according to the concentration creatinine and adding hydroxylamine hydrochloride to mixture,the organic acids with hydroxyl group were oximated to the ketobodies.Organic acids were extracted twice with ethyl acetate and ethyl ether and derivatized with BSTFA-TMCS.An the organic acids were determined with Agilent GC/MS 6890/5973i with scan model.the mass-to-charge ratio range is 50-550 m/z,all data were nalyzed with Agilent GCMSD ChemStationG1701DA.We also investigated the linearity, accurate,precision.recovery and Carry-over by determining the internal standards in normal samples and positive organic acids in spiked control samples.Results More than one hundred kinds of organic acids in urine samples can be analyzed with this method.According to the two internal standards in normal urine samples,the minimal detection limit MMA and 2.PA was 2.5-2.8 μmol/L.Intra-and interassay coefficient of variation for MMA and 2-PA are both less than 10%.Pre-processing Interassay coefficient by sequential preparations of the same sample was 14%.The recoveries of the spiked samples were 95%-105%.Carryover analysis was less than 1%.All the parameters meet the requirement for clinical diagnosis.12 samples demonstrated positive including 6 cases of methylmalonic acidemia,1 case of propionic acidemia,3 cases of tyrosinemia Ⅰ,1 case of maple syrup urine disease and 1 cases of ketosis.Conclusions The method for the determination of organic acids in urine by GC/MS has been successfully established.It can be used for clinical screening and diagnosis for inherited genetic metabolic diseases.