STATISTICAL PITFALLS IN THE COMPARISON BETWEEN 2 COMMERCIAL SERUM FERRITIN KITS, PHARMACIA AND AMERSHAM

Two commercial ferritin kits, Phadebas Ferritin PRIST (kit B) and Ferr itin RIA Amersham (kit A) were compared in order to ''translate'' ferr itin values from one kit to the other. Ferritin levels in 222 sera wer e determined with both kits in the concentration range 5-838 mug/l. Re gression analysis disclosed a parabolic regression between the logarit hmically transformed results obtained with the two kits. Measured kit B values of 10, 12, 15, 30 and 300 mug/l corresponded to calculated ki t A values of 15, 17, 20, 34 and 321 mug/l, respectively. In kit A, st orage of sera for two years at -25-degrees-C in combination with freez e-thawing three times produced a minor fall (p<0.0001) in ferritin lev els with a median percent decline of 16%.