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Change to insulin-like growth factor-1 reference intervals

31 March 2021

Effective today, SA Pathology has changed its testing platform for insulin-like growth factor-1 (IGF-1) from the IDS-iSYS platform to the Diasorin LiaisonXL platform. This change will immediately have impact on values and reference intervals reported.

For two years SA Pathology has prepared for this change, collecting data for each patient using both platforms. Our data indicates results from the LiaisonXL platform are approximately 20% higher than the iSYS platform. This difference is despite both assays being harmonised to an internationally recognised standard, the World Health Organization first IS 02/254 for insulin-like growth factor-1.

Fig 1: Passing bablok fit of patient comparison data, n=2818

The new Diasorin reference ranges are based on studies across 6 different clinical sites in the US and Europe, where 4419 samples were obtained from subjects belonging to an apparently healthy population with no evidence of endocrine disorders.  The samples were selected and split into groups identified by gender and age: 302 infants, 865 adolescents, 1646 children and 1606 adult samples. 

Figure 2: Female and male upper and lower reference limits (Diasorin LIAISON IGF-1 reference ranges document 07/13)

The Diasorin reference ranges differ from those from the IDS ranges used on the iSYS platform. Figure 3 below is a graphical representation of the reference range comparison for each sex. 

Figure 3: Comparison of iSYS and Liaison upper and lower reference limits for females and males

Our evaluation shows the move to the Liaison platform will result in an increase in the number of patients with results outside the reference intervals, increasing from 16.2% to 18.1%. Of those patients with discrepant results (comparisons with a result inside RI on one platform and outside RI for the other), 80% are within 5 nmol/L of the age specific reference limit. This may reflect differences between the populations used to determine reference intervals by either of the manufacturers and the SA population.

SA Pathology’s plan at this time is to use the published Diasorin reference intervals, accepting we expect to see an increase in the number of patient’s results outside reference intervals, particularly in men. These ranges were established from a large international study and are suitable for use. SA Pathology aims to consult further with Diasorin and other Australian Pathology providers to build Australian-based reference intervals.

For the next six months (April to September 2021), SA Pathology IGF-1 reports will show the current LiaisonXL result, and where there has been a previous IGF-1 request within the past 2 years, both the iSYS and Diasorin results will be included as a comment.


Dr Tom Dodd
Clinical Service Director

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