A case of concurrent Hemoglobin Lansing‐Ramathibodi and Hemoglobin Constant Spring with falsely low oxygen saturation detected by pulse oximetry

A 3-year-old Thai girl was treated for simple gingivitis under general anesthesia. Her pulse oximeter oxygen saturation (SpO2) was 85%–90%. There were no abnormal findings other than low SpO2 during and after her treatment. The patient was not short of breath in daily life and ran around like other kids. She was referred to Jichi Medical University, Children's Medical Center for further investigation of her low SpO2 level. Her father was Thai and had no underlying disease. Her mother was also Thai, had anemia and asthma, and her SpO2 was reported to be approximately 90% when it was first measured by a previous physician. The patient's maternal grandfather also had anemia. The patient's SpO2 was 85% at the time of examination. Arterial blood gas analysis showed that arterial partial pressure of oxygen (PaO2) was 106.1 mmHg and arterial oxygen saturation (SaO2) was 97.3%, which was not consistent with the low SpO2. Methemoglobinemia was ruled out by a MetHb measurement of 0.3%. Blood tests showed a red blood cell count of 4.28 × 1012/L, hemoglobin (Hb) concentration of 10.1 g/dL, hematocrit of 31.5%, MCV of 73.5 fL, reticulocyte count of 4.6%, HbA1c 4.0%, total bilirubin of 0.66 mg/dL, direct bilirubin of 0.05 mg/dL, serum iron of 63 μg/dL, ferritin of 22.4 ng/mL, and haptoglobin of <10 mg/dL. Coomb's test, Sugar water test, and Ham test were all negative. No abnormalities were found in erythrocyte morphology on blood smears. Considering her country of origin, abnormal Hb was suspected. The HPLC glycohemoglobin analyzer method in our lab, which has the advantage of being able to detect abnormal Hb secondarily, showed an unknown peak (Figure 1a). The isopropanol screening test for abnormal Hb, which indicates hemoglobin instability, was positive in 15 min. Electrophoresis and isoelectric focusing of hemoglobin also showed an abnormal band (Figure 1b). Both tests were performed at Fukuyama Clinical Laboratory. Therefore, genetic analysis was performed, at the 87th codon of α1 globin, histidine was replaced by glutamine, and Hb Lansing-Ramathibodi (LR) heterozygosity was detected (Figure 1c). In addition, the 142nd terminating codon of the α2-globin gene was replaced by glutamine, indicating Hb Constant Spring (CS) heterozygosity (Figure 1d). Hb-CS is denoted as (α CS α/αα) and this genotype corresponds to heterozygous α-thalassemia 2. β-globin gene sequencing revealed no abnormalities. The mother's blood test results showed an Hb concentration of 12.0 g/dL, MCV of 83.3 fL, tests for abnormal hemoglobin, and Hb-LR was detected in genetic testing. No abnormalities were found in other tests. Hb-LR was detected in this patient and in her mother, both of whom had low SpO2. Furthermore, this patient, who showed mild microcytic anemia had concurrent Hb-CS. Hb-CS is a non-deletional form of abnormal hemoglobin with alpha thalassemia-like symptoms that is frequently detected in Southeast Asia.1 Although we could not examine her father, we suspect that the mild microcytic anemia observed in this patient may have been due to Hb-CS inherited from her father and Hb-LR inherited from her mother. To the best of our knowledge, concurrent Hb-CS and Hb-LR has never been reported. The first report of Hb-LR in Asia was reported by a Japanese in 20122 and by a Thai family in 2016.3 It is thought that many cases are relatively rare and not investigated. Pulse oximeters are a simple way to estimate arterial blood oxygen saturation, but they can give falsely low readings due to abnormal Hb. Pulse oximetry uses two light wavelengths (660 and 940 nm) emitted across a vascular bed to calculate the relative proportions of oxy- and deoxyhemoglobin based on their different absorption spectra.4 For example, the oxyhemoglobin of Hb Bonn has higher absorbance at the 660 nm wavelength, resulting in erroneously low SpO2.5 In contrast, low SpO2 in Hb-LR is likely due to Hb instability. Hb-CS is a non-deficient form of abnormal Hb associated with alpha thalassemia-like symptoms that is frequently detected in Southeast Asian patients. Asymptomatic abnormal Hb and mild forms of thalassemia may be overlooked. Glycohemoglobin analysis may show abnormal histograms or abnormal peaks, so first this screening test would be recommended. Since special reagents and equipment are required for definitive diagnosis, the further analyses at Fukuyama Clinical Laboratory would be recommended. Our data suggest the importance of investigating the possibility of abnormal Hb in patients with low SpO2, but without signs of cardiopulmonary disease, to avoid unnecessary treatment and testing. Moreover, with increasing international migration, it is likely that clinicians will diagnose various types of abnormal Hb disease in Japan. K.T. collected and analyzed the data, prepared the figure, and drafted the manuscript. Y.H and T.Y. reviewed and revised the manuscript. T.S. and A.S. managed the patients. A.S. coordinated and supervised data collection and reviewed and revised the manuscript. All authors read and approved the final manuscript. We thank Prof. Hitoshi Kanno and Dr. Takako Aoki from Department of Transfusion and Cell Processing, Tokyo Women's Medical University for the excellent genetic analysis. We thank Leah Cannon, PhD, from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript. The authors declare no conflict of interest. Informed consent was obtained from the parents of the patient to publish the data in this report.