Abstract

The acidosis known to be associated with sickle cell anaemia is exploited in this work to estimate its energy cost to the kidney that has to dialyse the excess protons from the blood into urine against a concentration gradient, thereby doing significant extra work. The mean blood and urine pHs measured for the four discrete sickle cell states (42 subjects with approximately equal numbers of males and females per group, to minimise sex bias) are: HbAA = 7.39 ± 0.07 and 6.54 ± 0.15, HbAS = 7.35 ± 0.09 and 6.44 ± 0. 15, HbSS = 7.32 ± 0.08 and 5.89 ± 0. 39, HbSS-crisis = 7.15 ± 0.12 and 4.75 ± 0.46, respectively. From these data, the estimated enthalpies of dialysis, DH_d, for each of the four states are: HbAA = 1.96RT ≈ 4.94 kJ, HbAS = 2.10RT ≈ 5.29 kJ, HbSS =3.29RT ≈ 8.29 kJ, and HbSS-crisis = 5.53RT ≈ 13.93 kJ. The estimated entropies of dialysis, TDS_d, compared to the normal HbAA state are: HbAA = 0.00RT ≈ 0.00 kJ; HbAS = 0.14RT ≈ 0.35 kJ, HbSS = 1.34RT ≈ 3.38 kJ and HbSS-crisis = 3.57RT ≈ 8.99 kJ (R = 8.31J-mol^-1K^-1 and T = 303K). The conclusion from this work is that sickle cell disease is very energy costly to the kidney as most of the energy for proton dialysis is wasted as a result of high entropy.

Key words: Sickle cell, anaemia, energy, kidney, dialysis, proton, and enthalpy