State of the art of aldoSterone ImmunoaSSayS. a multIcenter collaboratIve Study on the behalf of the cardIovaScular bIomarkerS Study Group of the ItalIan SectIon of european SocIety of lIGand aSSay (elaS) and SocIetà ItalIana dI bIochImIca clInIca (SIbIoc)

Antonio Fortunato1, Concetta Prontera2, Silvia Masotti2,3, Maria Franzini2,3, Cristina Marchetti1, Stefania Giovannini4, Gian Carlo Zucchelli4, Michele Emdin2, Claudio Passino2,3, Aldo Clerico2,3

1Clinical Chemistry Laboratory, San Bortolo Hospital, Vicenza, Italy; 2Department of Cardiovascular Medicine and Laboratory Medicine, Fondazione CNR‐Regione Toscana G. Monasterio, Pisa, Italy; 3Institute of Life Science, Scuola Superiore Sant’Anna, Pisa, Italy; 4QualiMedLab srl, Pisa, Italy

Aldosterone, the primary member of the class of mineralocorti‐coids, is exclusively produced by the zona glomerulosa of the adrenal cortex and mainly acts on the distal renal tubule by increasing sodium reabsorption and potassium excretion, thus controlling sodium and potassium metabolism. The knowledge of aldosterone levels is very usefull in screening and diagnosis of primary aldosteronism. Immunoassays normally used in routine laboratory for aldosterone measurements are usually made by manual. The reference techniques require very expensive equipment, skilled staff and are more time consuming. Recently fully automated methods for aldosterone assay are available and needs to be clarified if the use of these platforms could improve some flaws of commonly used manual assays.

In this study analytical performances of two automated aldosterone assays, IDS iSYS and DiaSorin LIAISON®, were evaluated. Results obtained with the two platforms for clinical samples (healthy subjects and patients with cardiovascular disease and/or hyperaldosteronism) were compared with those obtained by immunoassays (RIA and EIA) or separative methods (GC‐MS and LC‐

MS). Aldosterone was also measured with the two automated methods in the control specimens distribute during the last two annual cycles of a national External Quality Assessment scheme named Immunocheck study.

1400

1200

1000

800

600

400

200

00 200 400 600 800 1000 12001200 1400

Aldosterone measured by iSYS platform, pg/mL

Ald

ost

ero

ne

mea

sure

d b

y LI

AIS

ON

pla

tfo

rm, p

g/m

L R=0. 906N= 294Y = 25.915+0.873 X

40

35

30

25

20

15

10

5

00 50 100 150 200 250 300 350 400

Aldosterone concentration, pg/mL

CV, %

LIAISON methodiSYS method

BACkGround

MEthodSCorrelation matrix between consensus mean and plasma aldosterone values measured with the immunoassay methods used by participant laboratories in the 12 control study samples distributed in the EQA study.

               

               

               

               

               

               

               

               

 

 

 

 

 

 

 

CM

SOR

IMT

LSN

DRG

DPC

DSL

IDSY 

CM

1.000

0.994

0.966

0.964

0.759

0.958

0.977

0.990 

SOR

0.994

1.000

0.937

0.981

0.710

0.976

0.988

0.989 

IMT

0.966

0.937

1.000

0.875

0.845

0.896

0.899

0.947 

LSN

0.964

0.981

0.875

1.000

0.626

0.965

0.994

0.972 

DRG

0.759

0.710

0.845

0.626

1.000

0.645

0.652

0.738 

DPC

0.958

0.976

0.896

0.965

0.645

1.000

0.966

0.958 

DSL

0.977

0.988

0.899

0.994

0.652

0.966

1.000

0.974 

IDSY

0.990

0.989

0.947

0.972

0.738

0.958

0.974

1.000 

 

 

 

 

 

 

    

METHODS

LIAISON

iSYS  

 LoB

pg/mL

18.0

19.1 

LoD  pg/mL  

30.2  

33.2  

 

 LoQ  at 20% CV

pg/mL  

40.0

37.6  

Comparison of analytical sensitivity parameters of the immunoassay methods for plasma aldosterone using the LIAISon® and iSYS platforms.

CM: consensus mean; Sor: RIA DiaSorin; IMt: RIA Immunotech; LSn: LIAISON® DiaSorin; drG: ELISA DRG; dPC: RIA Siemens; dSL: RIA Diagnostic System Laboratories; IdSY: iSYS IDS.

Our data indicate that aldosterone values measured with the two automated methods actually show better analytical performances, shorter TAT and require less “hands on labor” com‐pared to other RIA and EIA immunoassays. Furthermore, the analytical performance of the two automated aldosterone immunoassays are quite similar.

ConCLuSIonS

The two automated methods showed similar analytical performances: LoD 30.2 vs 33.2 pg/mL, LoQ 37.6 vs 40.0 pg/mL respectively; the within‐run and total imprecision evaluation showed CV% between 8.1 and 14.1 for samples with 65.1 and 139.4 pg/mL concentration for both methods. There was a close linear regression between methods, however we found a significant bias (mean 27.5%, SD 59.5%) between LIAISON® and iSYS. In the evaluation of the EQA samples results obtained with these two methods were highly correlated to the consensus mean values.

rESuLtS