Analytical quality goals for parathyroid hormone based on biological variation.
BACKGROUND
Measurement of parathyroid hormone (PTH) is central in the investigation of pathologies of bone and mineral ion metabolism. Knowledge of the biological variation of an analyte forms an essential part of evaluating a new analyte, enabling the objective assessment of changes in serial results and the utility of reference intervals, as well as establishing laboratory quality specifications.


METHODS
This study determined the biological variation of PTH in 20 healthy individuals, which was calculated according to the familiar methods outlined by Fraser and Harris.


RESULTS
The within-subject variation was 25.3% and the between-subject variation was 43.4%. The critical difference for sequential values significant at p<0.05 was calculated as 72%. The within-subject variation forms a relatively small part of the reference interval, shown by the low index of individuality of 0.58. Objective analytical quality goals have also been established, revealing achievable optimum performance for imprecision of approximately 6%. The desirable analytical bias goal was approximately 12%.


CONCLUSIONS
This study has objectively shown that the analytical precision of current instruments is being achieved contrary to the known problems surrounding the analytical bias for PTH assays. The limitations of using reference intervals for PTH, both in diagnoses and monitoring, are shown.
Department of Clinical Biochemistry, Lister Hospital, Stevenage, UK. adie.viljoen@nhs.net
Adie
A
Viljoen
Dhruv K
DK
Singh
Patrick J
PJ
Twomey
Ken
K
Farrington
D000328:Adult; D016477:Artifacts; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000032:analysis*; D011786:Quality Control; D012680:Sensitivity and Specificity; D055815:Young Adult
D010281:Parathyroid Hormone