Application of Sigma Metrics for the Assessment of Quality Assurance for Plasma Amino Acid Analysis in Biochemical Genetics Laboratory in Pakistan

Document Type

Conference Paper


Pathology and Microbiology



Quality is assessed on sigma scale with 3 sigma as the minimum allowable sigma and 6 being world-class quality goal. We aim to present sigma-metrics of plasma amino acids (AA) observed in our Biochemical Genetics Laboratory (BGL).


Internal quality control (IQC) data of AA run in BGL was analyzed from 2013 -2014. Two years mean from IQC and proficiency testing (PT) results were utilized to establish coefficient of variation (CV) and bias respectively. Bias (%): (mean of all laboratories using same instrument-BGL AKU mean)/(mean of all laboratories using same instrument)*100. Sigma metrics were then calculated: ∑(σ)= (total allowable error – bias%)/CV.

Results: Overall CV of individual AA ranged from 3.46-11.2%. The laboratory mean and PT target mean showed6. Plasma asparginine, histidine, glutamine and aspartate elicited < 3 on sigma-scale. We achieved sigma metrics of the range 3.1–5.9 for remaining amino acids. Of all the amino acids evaluated the average sigma level was 4.8.

Conclusion: Satisfactory sigma metrics were achieved for all AA. The AA below3 sigma must be evaluated with discretion and strict quality control checks. Work Done By Section of Chemical Pathology, Departments of Pathology and Laboratory Medicine and Pediatrics and Child Health*, Aga Khan University Hospital (AKUH)


Society For The Study of Inborn Error of Metabolism