A 50-Year-Old Woman with Severe Resting Hypoxia not Amendable to High-Flow Oxygen Supplementation

Pulse oximetry is a widely used non-invasive method to measure arterial oxygen saturation (SpO₂). However, haemoglobinopathies, including rare low-oxygen-affinity variants such as haemoglobin (Hb) Lansing can result in falsely low SpO₂ readings due to alterations in the Hb oxygen dissociation curve and spectral properties. Recognising these conditions is crucial to avoid misdiagnosis and unnecessary interventions.

A 50-year-old female with a history of chronic obstructive pulmonary disease (COPD), hypertension and compensated cirrhosis presented for pre-operative evaluation. Persistent hypoxia (SpO₂ 84%), unresponsive to oxygen supplementation, was noted during routine assessment. Diagnostic investigations excluded pulmonary or cardiac shunts, hepatopulmonary syndrome and common causes of methaemoglobinaemia or carboxyhaemoglobinemia. Arterial blood gas analysis using a CO-oximeter revealed a true oxygen saturation of 90%, highlighting a discrepancy with pulse oximetry. Hb electrophoresis demonstrated an abnormal haemoglobin fraction, and subsequent genetic testing identified a heterozygous mutation (HBA1: c.264C>G), confirming Hb Lansing. The patient was asymptomatic apart from mild exertional dyspnoea attributed to underlying COPD and safely underwent planned surgery.

Hb Lansing is a rare haemoglobinopathy characterised by low oxygen affinity and high p50, leading to falsely low SpO₂ readings and minimal response to supplemental oxygen. Diagnosis relies on CO-oximetry, Hb electrophoresis and genetic analysis. No specific treatment is required for low-affinity haemoglobinopathies, which generally have a benign clinical course.

Haemoglobinopathies should be considered in the differential diagnosis of unexplained hypoxia. Utilisation of targeted diagnostic tools enables clinicians to ensure accurate diagnosis and appropriate management.

The differential diagnosis of hypoxia, non-amendable to supplemental oxygen in a stable patient mainly includes right to left pulmonary or cardiac shunt, or a haemoglobinopathy with altered oxygen affinity.Clinicians should be familiar with instances in which pulse oximetry is not reliable, including poor tissue perfusion, certain nail polish types and haemoglobinopathies, and should obtain arterial blood gas for accurate assessment.If haemoglobinopathy is suspected, it is advisable to perform arterial blood gas analysis using a multi-wavelength spectrometer for accurate assessment.Early performance of haemoglobin electrophoresis followed by mutational analysis will yield diagnosis and prevent further work-up.The clinical course of low-oxygen-affinity haemoglobinopathies is mild, and patients should not be denied necessary surgical interventions due to this condition.