A plea for intra-laboratory reference limits. Part 2. A bimodal retrospective concept for determining reference limits from intra-laboratory databases demonstrated by catalytic activity concentrations of enzymes.
Clin Chem Lab Med
; 45(8): 1043-57, 2007.
Article
en En
| MEDLINE
| ID: mdl-17867994
ABSTRACT
BACKGROUND:
The current recommendations for establishing intra-laboratory reference limits (RLs) cannot be fulfilled by most laboratories because of the expense involved. In the current study, a bimodal method was developed to derive RLs from data stored in a laboratory information system without any assumption concerning the distribution of the diseased subgroup.METHODS:
A smoothed kernel density function (D(mix)) was estimated for the distribution of combined data for non-diseased and diseased adult subjects. It was assumed that the "central" part of the distribution represents the non-diseased population, which was defined and used to estimate a Gaussian distribution of either the original values or Box-Cox transformed data. This normal distribution was now considered the distribution of the non-diseased subgroup (D(nd)). Percentiles were calculated to obtain retrospective RLs. The density function of the diseased subgroup (D(d)) was calculated by subtracting the non-diseased density function from D(mix) (D(d)=D(mix)-D(nd)). The intersection point of the D(nd) and D(d) curves identified the RL with the highest diagnostic efficiency.RESULTS:
The model was applied to catalytic activity concentrations of several enzymes with data from different laboratories. The RLs obtained were similar to recently published consensus values. Differences between laboratories were small but significant. Gender stratification was necessary for alanine aminotransferase (ALT), aspartate aminotransferase (AST), and gamma-glutymaltransferse (gamma-GT), not significant for lipase and amylase and inconsistent among the laboratories for alkaline phosphatase (AP) and lactate dehydrogenase (LDH). Age stratification was only tested for two groups (18-49 and >or=50 years) and was significant for AST (females only), gamma-GT and lipase, not significant for amylase and inconsistent for AP, LDH and ALT. For gamma-GT, further stratification for age in decades was necessary for males. Creatine kinase MB (CK-MB) values were not stratified owing to the low number of data available.CONCLUSIONS:
Retrospective RLs derived from intra-laboratory data pools for the catalytic activity concentration of enzymes using a modified procedure plausibly agreed with published consensus values. However, most RLs varied significantly among laboratories, thus supporting the "old" plea for intra-laboratory RLs.
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Valores de Referencia
/
Modelos Estadísticos
Tipo de estudio:
Guideline
/
Risk_factors_studies
Idioma:
En
Revista:
Clin Chem Lab Med
Asunto de la revista:
QUIMICA CLINICA
/
TECNICAS E PROCEDIMENTOS DE LABORATORIO
Año:
2007
Tipo del documento:
Article
País de afiliación:
Alemania
Pais de publicación:
ALEMANHA
/
ALEMANIA
/
DE
/
DEUSTCHLAND
/
GERMANY