ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 P674

Long-term storage of blood spots: is retesting for newborn 17 OH-progesterone reliable?

Laurence Dolomie-Fagour, Dominique Gualde & Jean-Benoit Corcuff

CHU Haut-Lévêque, Pessac, France.

Congenital adrenal hyperplasia (CAH) screening programs are based on 17 OH-progesterone (17OHP) assay in dried blood spots sampled 3d after birth (samples >50 nmol/l are retested as duplicates and the alert threshold is 60 nmol/l). These programs have improved the diagnostic rate of the salt-wasting form. Confronted to delayed hyperandrogenic diagnosis in older children physicians sometimes request retesting years old dried blood spots to rule out erroneous initial true negative screening for CAH. We thus undertook investigation about the reliability of performing 17OHP assays in blood spots up to 10-year-old.

Blotter paper were stored on shelves at room temperature with no autoclaving; samples from odd years from 1997 to 2005 were retested in 2007 (original values distributed from undetectable levels of 17OHP to moderately above recall threshold). No samples from patients with proven CAH were used. Before assays the papers were left 4 days in the laboratory to ascertain uniform inter-sample dryness. 17OHP was assayed using Cisbio assay kit (interassay CV at the alert threshold 7.5%).

We evaluated the variation of 17OHP values between initial and delayed. 17OHP re-assayed in old blood spots was significantly lower than the initial value (P<0.0001). A moderate loss of immunoreactivity occured (4 first years) accelerating later on: total decrease in spots aged 2 years −19%, aged 4 years −19%, aged 6 years −24%, aged 8 years −41% Table: median (5%–95%).

17OHPDelta (nmol/l)Delta (nmol/l per year)Delta (%/year)
1997–200768 (37;139)15.4 (1;33.3)1.5 (0.1;3.3)3 (0;5)
1999–200754 (27;139)19.4 (11.6;58.2)2.4 (1.5;7.3)5 (3;6)
2001–200756 (26;162)10.8 (−2.5;69.6)1.8 (−0.4;11.6)4 (−1;7)
2003–200753 (26;121)9.4 (−0.2;40.2)2.3 (0.0;10.0)5 (0;10)
2005–200763 (27;140)9.1 (−3.5;40.5)4.6 (−1.7;20.3)9 (−2;19)

The global decrease and the large inter-spot variability of values elicits suspicion about the reliability of re-assaying 17OHP on spots from specific individuals.

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