Haemoglobin-oxygen affinity

Description:

Rarely performed.

Specimen:

1 mL blood in heparinised syringe (haemoximetry) or 5 mL blood in lithium heparin tube (tonometry).

Method:

Haemoximetry; Tonometry.

Reference Interval:

P50 O2: 3.4-3.8 kPa (25-29 mmHg).

The P50 O2 is the partial pressure of oxygen at which Hb is 50% saturated.

Application:

Investigation of patients with suspected Haemoglobinopathy due to a high oxygen affinity haemoglobin variant (unexplained erythrocytosis).

Investigation of patients with a likely abnormality of oxygen carriage and release due to an acquired abnormality eg, acidosis, alkalosis, hypoxaemia, carboxyhaemoglobin.

See also Haemoximetry.

Interpretation:

Decreased P50 O2 indicates increased oxygen affinity and decreased release ('shift to the left').

Increased P50 O2 indicates decreased oxygen affinity and increased release ('shift to the right').

Reference:

Bain et al. Dacie and Lewis Practical Haematology. 11th Ed. 2012.