Red cell volume measurement - using indium as a replacement for chromium.

The withdrawal of Cr-51-chromate has meant that the technique commonly used for direct measurement of red cell volume has had to be replaced. Most centres moved to a Tc-99m erythrocyte label, however, Tc-99m is known to dissociate over time. We have investigated an alternative technique using an In-111-chloride and tropolone solution and tested this both in vitro and in vivo. Initial in-vitro and in-vivo work, which included a check of the stability of the radio-labelled product at one hour, demonstrated this label to be stable over this time period. To date, 20 patients have undergone this technique and results show that this technique is a viable alternative to Cr-51-chromate particularly for patients with splenomegaly who require late sampling. This procedure is now in routine use in our institution.