What HbS target should I use?

For chronic stroke prevention and acute ischaemic stroke a target HbS below 30% is standard. For acute chest syndrome or pre-operative preparation a target of 30% is also common, while a single simple transfusion often aims nearer 50%. Always follow your local apheresis protocol.

How is the exchange volume calculated?

The fraction of cells remaining (FCR) equals the target HbS divided by the starting HbS. The patient's red cell volume is total blood volume times haematocrit. The donor red cell volume needed is the red cell volume times one minus FCR, adjusted by an efficiency factor because exchange is never perfectly isovolaemic.

How is total blood volume estimated?

The calculator uses Nadler-style weight-based estimates: roughly 70 mL/kg for adult men, 65 mL/kg for adult women, and 70 to 80 mL/kg for children. These are population averages, so confirm against the patient's measured values where available.

What haematocrit should the replacement blood have?

Packed red cells are typically assumed to have a haematocrit near 60 to 70%. The tool divides the required donor red cell volume by the unit haematocrit to estimate the whole volume of product, which is what an apheresis machine actually moves.

Is this calculator a substitute for apheresis software?

No. It reproduces the standard exchange equations for education and bedside cross-checking. Automated red cell exchange should always be programmed on validated apheresis equipment with a transfusion specialist confirming every parameter.

Sickle Cell Exchange Transfusion Volume Calculator

Red cell exchange transfusion removes a patient’s sickle haemoglobin (HbS) containing red cells and replaces them with donor cells, lowering the HbS percentage rapidly without raising blood viscosity. It is central to stroke prevention and to managing acute complications in sickle cell disease.

How it works

The exchange is driven by the fraction of cells remaining after the procedure:

FCR        = target HbS / starting HbS
TBV        = weight (kg) x volume factor (mL/kg)
RBC volume = TBV x haematocrit
donor RBC  = RBC volume x (1 - FCR) / efficiency

Here TBV is total blood volume, estimated from weight, and the efficiency factor (commonly about 0.9) accounts for the fact that an exchange is not a perfect one-for-one replacement. Dividing the donor red cell volume by the haematocrit of the packed unit gives the whole product volume the machine must process.

Worked example and notes

A 70 kg adult man with a haematocrit of 0.30 and a starting HbS of 80% who needs a target HbS of 25% has an FCR of 0.31. His total blood volume is about 4900 mL and his red cell volume about 1470 mL, so the donor red cell volume needed is roughly 1470 x (1 - 0.31), about 1010 mL before efficiency adjustment. At a unit haematocrit of 0.65 that is around 1550 mL of packed cells, or close to six standard units. Always confirm targets and volumes with the apheresis service, and remember that simple transfusion alone cannot safely reach low HbS targets because of viscosity limits.