Graphic representation of the correlations between age and protein S–related determinants in normal (•) and protein S–deficient (□) family members (see Table 1). (A) Comparison between total protein S antigen and age. The limits of the reference range (219 to 407 nmol/L) have been superimposed (- - -). The increased level compared with the reference range as age increases can be clearly seen. Correlations were significant in both groups. Although this results in a type III protein S–deficient phenotype in some older individuals, the level is still reduced compared with that in normal family members of comparable age. (B) Comparison between free protein S antigen and age. The limits of the reference range (56 to 182 nmol/L) have been superimposed (- - -). In all protein S–deficient family members, the level remained well below the limit of the normal range. Neither of the correlations were significant. (C) Comparison between C4bBP-β+ antigen and age. The correlation was significant for normal family members, and although significance is not reached in protein S–deficient family members, there is a tendency for an increase.