INTRODUCTIONThe analysis of amino acids in plasma and urine was introduced in Singapore when a laboratory for the investigation of inherited metabolic disorders was established by the Ministry of Health. Reference ranges are required for interpreting test results and making diagnoses. Initially, reference ranges established for Caucasians were used as there were no local data and we were unable to find data obtained by the same analytical method for Asian populations. This was not considered an ideal and long-term solution, as Singaporeans may have amino acid concentrations quite different from those of Caucasians due to genetic factors, dietary difference, environment, and other influences. This study was therefore undertaken when a number of healthy laboratory personnel volunteered to provide specimens for the study.

MATERIALS AND METHODSSixty healthy male and female laboratory workers not on any form of medication were recruited. They consisted of 24 males (range, 23 to 58 years) and 36 females (range, 20 to 60 years), with a mean age of 38.7 years. Non-fasting random blood and urine specimens were collected on ice. Removal of protein and peptides from heparinised plasma and urine was achieved by ultrafiltration through protein-exclusion membrane. Amino acid analysis on the ultrafiltrate was performed by a dedicated Beckman 6300 Amino Acid Analyzer using a cation exchange resin column and post-column colour reaction with ninhydrin reagent. Urine creatinine was measured by a Beckman LX 20 PRO Analyzer. Results for urine amino acids were expressed as micromol/mmol of creatinine.

RESULTSReference ranges for 32 amino acids in blood plasma and 36 amino acids in urine were calculated by a non-parametric method using the SPSS statistical calculation software. The ranges cover 95% of the population and the low and high limits of each reference range represent the 2.5th percentile and 97.5th percentile of the frequency distribution respectively.

CONCLUSIONSWe observed differences in the reference ranges of several plasma and urine amino acids between Singaporean and Caucasian populations. Moreover, the list of urine amino acids for Caucasian population is incomplete. We have therefore discontinued the use of reference values established for Caucasians and adopted the results of this study for our patient diagnostic work.

Adult ; Amino Acids ; analysis ; Asian Continental Ancestry Group ; European Continental Ancestry Group ; Female ; Humans ; Male ; Middle Aged ; Reference Values ; Singapore

INTRODUCTIONRecommended by the National Advisory Council of the Disabled, the Ministry of Health of Singapore supported a nationwide study of inherited metabolic disorders (IMDs). When the 5-year project ended, investigations were provided as a diagnostic service. This paper documents our 13-year experience.

MATERIALS AND METHODSPatients with symptoms suggestive of an IMD were referred. Investigations on heparinised blood and/or urine included amino acid analysis using a Beckman 6300 Amino Acid Analyser, organic acids analysis using a Hewlett- Packard gas chromatography and mass spectrometry, mucopolysaccharides quantitative assay and high-resolution electrophoresis, sugars by thin-layer chromatography.

RESULTSOf the 3656 patients studied from 1992 to 2005, IMDs were found in 127 (77 males; 50 females; age range, 1 day to 56 years). Their ethnic distribution was: 55.1% Chinese, 19.7% Malays, 11.0% Indians, 11.0% other races and 3.2% unknown. IMD diagnosed comprised 41 (32.3%) organic acidurias, 34 (26.8%) amino acidaemias/acidurias, 14 (11.0%) urea cycle defects, 15 (11.8%) mucopolysaccharidoses, 6 (4.7%) carbohydrate disorders and 17 (13.4%) others. Twenty-three (18.1%) cases were diagnosed during the neonatal period and 36 (28.3%) after the age of 13.

CONCLUSIONPositive detection rate was 3.5% and 48 IMDs were found. Significant proportion of cases had late-onset IMDs. Early identification of IMDs permits timely management, genetic counselling and prenatal diagnosis.

Adolescent ; Adult ; Amino Acids ; metabolism ; Biomarkers ; blood ; cerebrospinal fluid ; urine ; Carbohydrates ; blood ; Child ; Child, Preschool ; Chromatography, Gas ; Female ; Follow-Up Studies ; Glycosaminoglycans ; metabolism ; Humans ; Infant ; Infant, Newborn ; Male ; Mass Spectrometry ; Metabolism, Inborn Errors ; epidemiology ; metabolism ; Middle Aged ; Prevalence ; Prognosis ; Retrospective Studies ; Singapore ; epidemiology ; Urea ; metabolism

INTRODUCTIONThis paper shows the importance and value of external proficiency testing programmes in monitoring and improving a laboratory's diagnostic skills. It reviews and documents the wide variety of inherited metabolic disorders (IMDs) encountered in the programmes organised by the Human Genetics Society of Australasia and the College of American Pathologists.

MATERIALS AND METHODSThe programmes used actual patient specimens to assess a laboratory's ability to provide diagnoses based on laboratory tests results and brief clinical information. Participating laboratory was also required to suggest additional test(s) to confirm diagnoses.

RESULTSThe results of diagnoses on 116 samples were reviewed. Altogether 49 IMDs were encountered, including 26 organic acidurias, 16 aminoacidurias, 3 urea cycle defects, 5 mucopolysaccharidoses, and 1 each of mucolipidosis and purine disorder. Our report for 21 of the 116 samples (18.1%) deviated from the actual diagnoses. Deviations from the final diagnoses were recorded along with the reasons for them. The main reasons for the deviations were: the lack of standards for recognising metabolites of pathognomonic significance, absence of characteristic metabolites in samples collected during treatment, the presence of misleading unusual metabolites, inadequate clinical information, and inability to perform additional tests due to insufficient specimens.

CONCLUSIONSThe programmes provided a wide variety of IMDs, some of which we have yet to encounter in our patients. They also enabled us to learn about the varied biochemical manifestations at different stages of disease and the identity of previously unidentified metabolites. They enhanced our knowledge and experience and improved our diagnostic skills.

Australia ; Humans ; Laboratories ; standards ; Metabolism, Inborn Errors ; diagnosis ; New Zealand ; Pathology, Clinical ; standards ; Professional Competence ; Program Evaluation ; Quality Assurance, Health Care ; Quality Control ; Specimen Handling ; standards