Variables and formula

There are four variables, all patient parameters, required in the iron deficiency calculator:

■ The patient’s weight is used in the Ganzoni equation and also when establishing the iron stores. Although the original formula requires the weight in kilograms, values input in lbs are transformed.

■ Patient’s measured hemoglobin can be input in g/dL or mmol/L.

■ A target haemoglobin value is also input so iron deficit can be determined according to a specified individual target. Normal haemoglobin values are gender specific: for males from 13.8 to 18.0 g/dL (138 to 180 g/L, or 8.56 to 11.17 mmol/L) and females from 12.1 to 15.1 g/dL (121 to 151 g/L, or 7.51 to 9.37 mmol/L).

■ Iron stores are input as default 500 mg on the assumption that the patient weight is greater or equal to 35 kg (77 lbs). In case a pediatric patient with a weight below 35 kg is assessed, iron stores are calculated as 15 mg iron for each kg.

The Ganzoni equation is:

Total iron deficit (mg) = Weight in kg x (Target Hb - Actual Hb in g/dL) x 2.4 + Iron stores

In most cases, adult patients require a cumulative dose of elemental iron of at least 1 g. Most commonly, iron replenishment therapy is done intravenously:

■ As total dose (iron-dextran or iron – carboxymaltose);

■ As split dose (iron sucrose).