Are sex differences in blood cell count and hemoglobin moderated by the 2D:4D ratio? A cross‐sectional study in a Ghanaian population

Background and Aims: There are sex differences in blood cell count and hemoglobin (HGB) in adulthood due to differences in the levels of circulating sex hormones. The second‐to‐fourth digit ratio (2D:4D) is the putative marker of prenatal hormone exposure. The 2D:4D or the right‐left difference (Dr‐l) are sexually dimorphic and are correlates of sex hormones in adulthood. The study sought to determine whether sex differences in adult blood cell count and HGB can be partly explained by the 2D:4D or Dr‐l. Methods: The study was cross‐sectional between June and December 2021 at the University for Development Studies. The study involved 207 healthy participants (females = 113) aged from 18 to 32 years. The right‐hand (2D:4DR), and the left‐ hand (2D:4DL) digit ratio and their difference (Dr‐l) were measured using Computer‐ assisted analysis. Blood cell count, HGB, testosterone, and estradiol were measured from venous blood samples using an automated HGB analyzer and ELIZA technique. Results: The platelet count was inversely related to the 2D:4DR in the total sample with the 2D:4DR accounting for about 0.2% (adjR2 = 0.002) of the variability in platelet count. However, there was a sex difference as indicated by the significant interaction between sex and the 2D:4DR on platelet count (p = 0.03). The relationship between platelet count and the 2D:4DR was negative in females but positive in males. Also, there was a positive relationship between HGB concentration and the Dr‐l in the total study sample, where the Dr‐l accounted for about 0.6% (adjR2 = 0.006) of the variability in HGB concentration. Sex interacted significantly with the Dr‐l on HGB concentration (p = 0.01) such that the relationship between HGB and the Dr‐l was positive in females but negative in males. Conclusion: Prenatal hormone exposure, as indexed by the 2D:4D ratio, may partly account for the observed sex differences in platelet count and HGB levels in adulthood