Comparison between bone alkaline phosphatase immunoassay and electrophoresis technique in hemodialysis patients

Abstract

Background: Problem of the variability between the different methods using for bone alkaline phosphatase(bALP) determination greately influences the clinical significance of bALP as direct marker of bone metabolism.The aim of this study was to compare immunoassay with electrophoresis technique for bALP determination. Methods: We measured bALP in 71 patients on hemodialysis with agar gel electrophoresis (ISO-PAL, SEBIA) and immunoassay (OSTASE, Beckman Coulter).Results: The analyzed methods showed significant correlation (Spearman’s rho: 0.776, P < 0.01), but we found statistically significant (P < 0.01) positive bias (27%)for the results measured by immunoassay. In support of this, using electrophoresis technique we have detected presence of the intestinal isoenzymes of alkaline phosphatase in 55% of patients with median value of 30% of the total alkaline phoshatase and presence of liver-2 alkaline phosphatase isoform in 42% of patients with median value of 16.6%. The Kendall’s W of 0.787 (P<0.0001) revealed significant concordance between two analysed methods.Cusum test showed no significant deviation from linearity(P=0.850).Conclusions:Despite good agreement between immunoassay methods and electrophoresis technique for bALP determination, interchangeability between these two methods is questionable. Although immunoassays are increasingly used, as fully automated methods, in a large number of laboratories and become routine methods for bALP determination, it should be beared in mind, besidesvarious interferences, also the heterogeneity of the bALP itself, especially in patients on hemodialysis.

Uvod: Problem varijabilnosti između različitih metoda pomoću kojih se određuje koštani izoezim alkalne fosfataze (bALP) u velikoj meri utiče na klinički značaj bALP kao direktnog markera metabolizma kostiju. Cilj ove studije bio je poređenje imunohemijskog testa sa elektroforetskom tehnikom za određivanje bALP. Metode: bALP je određen kod 71 pacijenta na hemodijalizi, agar gel elektroforetskom tehnikom (ISO-PAL, SEBIA) i imunohemijskom metodom (OSTASE, Beckman Coulter). Rezultati: Analizirane metode pokazale su značajno slaganje (Spearmanov rho: 0,776, P < 0,01), ali je uočen statistički značajan (P < 0,01) pozitivan bias (27%) za rezultate izmerene imunohemijskom metodom. U prilog ovome, primenom elektroforetske tehnike, otkrili smo prisustvo intestinalnih izoenzima alkalne fosfataze u 55% bolesnika, sa srednjom vrednosti od 30% ukupne alkalne fostataze, kao i prisustvo jetrenih izoformi alkalne fosfataze kod 42% bolesnika sa srednjom vrednosti od 16,6%. Kendall-ov W od 0,787 (P < 0,0001) ukazivao je na značajno slaganje između dve analizirane metode. Cusumov test nije pokazao značajno odstupanje od linearnosti (P = 0,850). Zaključak: Uprkos tome što postoji dobro slaganje između imunohemijske metode i elektroforetske tehnike za određivanje bALP-a, međusobna zamenjivost ove dve metode je pod znakom pitanja. Iako se imunohemijske metode sve više koriste kao potpuno automatizovane, u velikom broju laboratorija i postaju rutinske metode za određivanje bALP-a, treba imati na umu, osim različitih interferencija, i heterogenost samog bALP, posebno kod bolesnika na hemodijalizi.