Unexpectedly low pulse oximetry measurements associated with variant hemoglobins: a systematic review

Hemoglobinopathy as a Rare Differential Disease for Low Oxygen Saturation by Pulse Oximetry: A Case Report and Literature Review

Pulse oximetry is used to screen for respiratory failure in dyspnea patients. However, pulse oximetry can yield false-positive results in certain situations. Unstable hemoglobinopathy is a disease in which mutations in the globin-encoding gene result in abnormal globin chain production, causing low percutaneous oxygen saturation (SpO2) levels due to changes in hemoglobin absorbance and oxygen affinity. We identified a new family lineage of Hb Hirosaki in an adult patient with chronic obstructive pulmonary disease, dyspnea, and low SpO2. According to our literature review, only a few cases of unstable hemoglobinopathy have been reported in adults. Most patients with unstable hemoglobinopathy are asymptomatic, and those with dyspnea often have respiratory diseases or severe anemia. To differentiate unstable hemoglobinopathy, an appropriate assessment of the discrepancy between SpO2 values and arterial blood gas analysis results is important.

Characterization of Hemoglobin Variants by Capillary Electrophoresis, UV-Vis, and FTIR Spectroscopy

Hemoglobinopathies, hereditary disorders affecting the structure or production of hemoglobin, were detected by routine HbA1c measurements by capillary electrophoresis (CE) at the University Hospital Motol, Prague. The potential of ultraviolet-visible (UV-Vis) and Fourier-transform infrared (FTIR) spectroscopy for the detection and characterization of hemoglobinopathies was investigated. FTIR spectra were recorded with a very high resolution (0.5 cm-1) with 128 scans. The broad amide I peak, located at 1700-1600 cm-1, can be formed by superimposition of the conformational structures of hemoglobin. These secondary protein structures were subjected to mathematical analysis. The application of band narrowing techniques, followed by curve fitting and integration processes, provided the basis for the quantitative estimation of protein secondary structure. As a result, unambiguous differences in UV-Vis spectra among patients with presumably normal hemoglobin, an HbC or a hemoglobin S/hemoglobin G (HbS/HbG)-Philadelphia variant could not be demonstrated. However, FTIR spectra indicated slight differences in α-helix, β-turns, β-sheet, or random coil secondary hemoglobin structures for these mutations. In the spectral wavenumber range of 950-850 cm-1, there were some obvious FTIR differences at specific wavenumbers between patients with normal hemoglobin and those with the HbC variant. Further investigations are needed with a sufficient number of hemoglobin variants to elucidate the potency of FTIR spectroscopy for the characterization of hemoglobinopathies.

Pitfalls in the diagnosis and management of acid-base disorders in humans: a laboratory medicine perspective

Diagnostic errors affect patient management, and as blood gas analysis is mainly performed without the laboratory, users must be aware of the potential pitfalls. The aim was to provide a summary of common issues users should be aware of.A narrative review was performed using online databases such as PubMed, Google Scholar and reference lists of identified papers. Language was limited to English.Errors can be pre-analytical, analytical or post-analytical. Samples should be analysed within 15 min and kept at room temperature and taken at least 15-30 min after changes to inspired oxygen and ventilator settings, for accurate oxygen measurement. Plastic syringes are more oxygen permeable if chilled. Currently, analysers run arterial, venous, capillary and intraosseous samples, but variations in reference intervals may not be appreciated or reported. Analytical issues can arise from interference secondary to drugs, such as spurious hyperchloraemia with salicylate and hyperlactataemia with ethylene glycol, or pathology, such as spurious hypoxaemia with leucocytosis and alkalosis in hypoalbuminaemia. Interpretation is complicated by result adjustment, for example, temperature (alpha-stat adjustment may overestimate partial pressure of carbon dioxide (pCO2) in hypothermia, for example), and inappropriate reference intervals, for example, in pregnancy bicarbonate, and pCO2 ranges should be lowered.Lack of appreciation for patient-specific and circumstance-specific reference intervals, including extremes of age and altitude, and transformation of measurements to standard conditions can lead to inappropriate assumptions. It is vitally important for users to optimise specimen collection, appreciate the analytical methods and understand when reference intervals are applicable to their specimen type, clinical question or patient.

Unmasking hemoglobin Köln: a rare cause of discrepancies between pulse oximetry and arterial oxygen saturation-a case report

Discrepancies between pulse oximetry and arterial oxygen saturation can pose challenges in clinical assessment. Possible underlying causes include poor peripheral perfusion, skin pigmentation, motion artifacts, and conditions like unstable hemoglobin and methemoglobinemia. Unstable hemoglobin variants, such as hemoglobin Köln, are rare inherited mutations affecting globin genes, potentially disrupting the folding, assembly, or interactions among subunits in globin molecules and the essential interactions between heme and globin for oxygen-binding properties. In this case report, we present the case of a 44-year-old Arabic woman who underwent extensive investigations due to disparities in pulse oximetry and arterial oxygen saturation, ultimately leading to the diagnosis of the unstable hemoglobin variant, hemoglobin Köln.

Chick sexing based on the blood analysis using Raman spectroscopy

Efforts are underway to develop technology for automatically determining the sex of chick embryos, aimed at establishing a stable and efficient poultry farming system while also addressing animal welfare concerns. This study investigated the possibility of chick sexing through blood analysis using Raman spectroscopy. Raman spectra were obtained from whole blood and its constituents, such as red blood cells (RBCs) and blood plasma, collected from chicks aged 1-2 days, using a 785-nm excitation wavelength. Principal component analysis (PCA) revealed statistically significant sex-dependent spectral variations in whole blood and RBCs, whereas blood plasma showed less clear dependency. These spectral differences between male and female chicks were attributed to differences in the proportion of spectral components from oxygenated (oxy-) and deoxygenated (deoxy-) RBCs, with males exhibiting a slightly stronger contribution of oxy-RBCs compared to females. This reflects the higher oxygen affinity of hemoglobin (Hb) in males compared to females. A model for discriminating chick sex was built using the ratios of certain Raman band characteristics of oxy-RBCs and deoxy-RBCs, achieving a sensitivity of 100%. This spectroscopic method holds promise for developing technology to discriminate the sex of early chicken embryos in ovo by detecting differences in oxygen saturation of RBCs based on sex.

Impact of Skin Pigmentation on Cerebral Regional Saturation of Oxygen Using Near-Infrared Spectroscopy: A Systematic Review

OBJECTIVES

Near-infrared spectroscopy (NIRS) is used in critical care settings to measure regional cerebral tissue oxygenation (rSo2). However, the accuracy of such measurements has been questioned in darker-skinned individuals due to the confounding effects of light absorption by melanin. In this systematic review, we aim to synthesize the available evidence on the effect of skin pigmentation on rSo2 readings.

DATA SOURCES

We systematically searched MEDLINE, Cochrane Database of Systematic Reviews, Embase, and Google Scholar from inception to July 1, 2023.

STUDY SELECTION

In compliance with our PROSPERO registration (CRD42022347548), we selected articles comparing rSo2 measurements in adults either between racial groups or at different levels of skin pigmentation. Two independent reviewers conducted full-text reviews of all potentially relevant articles.

DATA EXTRACTION

We extracted data on self-reported race or level of skin pigmentation and mean rSo2 values.

DATA SYNTHESIS

Of the 11,495 unique records screened, two studies (n = 7,549) met our inclusion criteria for systematic review. Sun et al (2015) yielded significantly lower rSo2 values for African Americans compared with Caucasians, whereas Stannard et al (2021) found little difference between self-reported racial groups. This discrepancy is likely because Stannard et al (2021) used a NIRS platform which specifically purports to control for the effects of melanin. Several other studies that did not meet our inclusion criteria corroborated the notion that skin pigmentation results in lower rSo2 readings.

CONCLUSIONS

Skin pigmentation likely results in attenuated rSo2 readings. However, the magnitude of this effect may depend on the specific NIRS platform used.

Heart Disease Screening and False Hypoxemia in the Neonate

BACKGROUND

Screening for congenital heart diseases by pulse oximetry is used for the initial assessment of the neonate. Variants of hemoglobin F can compromise light absorbance, inducing erroneous results.

CASE REPORT

Two infants screened for congenital heart disease showed an asymptomatic low peripheral oxygen saturation. Arterial blood gases analysis revealed a normal arterial pressure of oxygen and oxygen saturation. More likely and/or severe causes of hypoxemia were ruled out. This "artifact" with SpO2-SaO2 dissociation, and after exclusion of other common etiologies of hypoxemia, raised the clinical suspicion of hemoglobinopathy. Hemoglobin molecular and genetic studies identified specific mutations in gamma chains from hemoglobin F, named hemoglobin F Sardinia.

CONCLUSION

Hemoglobin F variants may result in low peripheral oxygen saturation readings by pulse oximetry, explaining the discordance in the clinical appearance and low peripheral oxygen saturation readings.

A Hemoglobin Variant Causing an Unexplained Low Oxygen Saturation by Pulse Oximetry: Two Case Reports

Pulse oximetry is now routinely used in neonatal resuscitation and for neonatal screening for congenital heart diseases. Beyond respiratory and cardiac diseases, hemoglobin (Hb) variants must be included in the differential diagnosis of low oxygen saturation detected by pulse oximetry. We aim to describe two cases of fetal Hb variant (heterozygous γ-globin gene (HBG1) mutation in exon 2 c.202G>A (p.Val68Met)), which was identified in two unrelated newborns.

Erythrocytes Functionality in SARS-CoV-2 Infection: Potential Link with Alzheimer's Disease

Coronavirus disease 2019 (COVID-19) is a rapidly spreading acute respiratory infection caused by SARS-CoV-2. The pathogenesis of the disease remains unclear. Recently, several hypotheses have emerged to explain the mechanism of interaction between SARS-CoV-2 and erythrocytes, and its negative effect on the oxygen-transport function that depends on erythrocyte metabolism, which is responsible for hemoglobin-oxygen affinity (Hb-O2 affinity). In clinical settings, the modulators of the Hb-O2 affinity are not currently measured to assess tissue oxygenation, thereby providing inadequate evaluation of erythrocyte dysfunction in the integrated oxygen-transport system. To discover more about hypoxemia/hypoxia in COVID-19 patients, this review highlights the need for further investigation of the relationship between biochemical aberrations in erythrocytes and oxygen-transport efficiency. Furthermore, patients with severe COVID-19 experience symptoms similar to Alzheimer's, suggesting that their brains have been altered in ways that increase the likelihood of Alzheimer's. Mindful of the partly assessed role of structural, metabolic abnormalities that underlie erythrocyte dysfunction in the pathophysiology of Alzheimer's disease (AD), we further summarize the available data showing that COVID-19 neurocognitive impairments most probably share similar patterns with known mechanisms of brain dysfunctions in AD. Identification of parameters responsible for erythrocyte function that vary under SARS-CoV-2 may contribute to the search for additional components of progressive and irreversible failure in the integrated oxygen-transport system leading to tissue hypoperfusion. This is particularly relevant for the older generation who experience age-related disorders of erythrocyte metabolism and are prone to AD, and provide an opportunity for new personalized therapies to control this deadly infection.

Unexpectedly low oxygen saturation in a child with a variant hemoglobin

We report a child with an unexpected low saturation reading despite normal values having been recorded soon after birth. A family history of Rothschild hemoglobin variant affecting the father was obtained. Saturation values improved with oxygen and anesthesia was uneventful. The development of low saturation values as the child matures is explained, and management for future health presentations outlined.

Understanding pulse oximetry in hematology patients: Hemoglobinopathies, racial differences, and beyond

Pulse oximetry (SpO₂ ) is a widely used, non-invasive method of estimating arterial oxygen saturation. Measurement of SpO₂ relies on comparing the relative absorption of light in the red and infrared regions with the expected absorption pattern of oxygenated and deoxygenation adult hemoglobin. As this screening tool has entered common clinical use, test limitations have emerged, including concern about the risk of overestimation of oxygen saturation by pulse oximetry in a disproportionate number of people with dark skin pigment, leading to potential for underdiagnosis of true hypoxemia. In addition, a range of challenges may arise in patients with increased levels of methemoglobin - whether acquired or inherited - carboxyhemoglobin, or in patients with a subset of inherited variant hemoglobins. It is important for Hematologists, and indeed all clinicians who rely on pulse oximetry, to understand the principles and limitations of this ubiquitous test.

Hemoglobin I-Toulouse: A rare hemoglobinopathy presenting with low oxygen saturations

We report a child with persistently low oxygen saturations (SpO2 90%-92%) [normal SpO2 > 98%], with delayed diagnosis due to the co-existing congenital pulmonary airway malformation with possible arterio-venous malformation. The diagnosis was only achieved after low oxygen saturations incidentally discovered from the child's father. The eventual cause was Hemoglobin I-Toulouse, making both patients the first reported cases with low oxygen saturations.

Hemoglobin Rothschild – Unimpaired physical performance and oxygen uptake – A case report with literature review

Asymptomatic patients with hemoglobin (Hb) variants can be detected by low oxygen levels in pulse oximetry (SpO₂).

Depending on the type of Hb variant, low SpO₂ values are either falsely low, with corresponding normal arterial oxygen saturation (SaO₂), or truly low, with low SaO₂ values, as observed in Hb variants with low oxygen binding affinity. In this context, attention must be paid to the method of determining SaO₂.

Low oxygen affinity Hb variants such as Hb Rothschild (HbR) might compensate for low oxygen loading in the lung through unloading more oxygen in peripheral tissues. This is the first case report to illustrate that maximal oxygen uptake and the workload are unimpaired in HbR variant patients.

An Investigation of Pulse Oximetry Levels during Swallowing in Healthy Adults and in Individuals with Severe and Very Severe Chronic Obstructive Pulmonary Disease

To compare pulse oximetry (PO) levels during swallowing in healthy adults and adults with severe chronic obstructive pulmonary disease (COPD). Participants included two groups of 60 healthy adults, balanced for gender. The young group ranged from 18 to 38 years, and the older group from 60 to 87 years. In addition, there were 11 participants with COPD aged 43 to 82 years. PO levels were collected as each participant swallowed 10 mL of water, 10 mL of applesauce, and a piece of diced pear (three trials each). Analyses for the healthy groups revealed neither statistically significant main effects for bolus type nor interactions between gender and age. For between-subject effects, there was no main effect for gender, but there was a large main effect for age, and a gender and age interaction. In the group with COPD, there were no significant differences across bolus types; however, PO measures were consistently lower than the healthy groups for all bolus types. Healthy adults exhibited stable PO levels across bolus types. Adults with COPD, although exhibiting significantly lower PO levels, also remained stable. For clinicians who monitor PO measures, these results offer a more comprehensive understanding of the nature of these measures during swallowing in these groups.

A family of three with haemoglobin Cheverly: low oxygen saturation in stable patients

Haemoglobin (Hb) Cheverly is a rare, low oxygen affinity haemoglobinopathy. It is a result of point mutation at the 45 codon of the beta globin genes that leads to substitution of phenylalanine by serine. It is characterised by spuriously low peripheral oxygen saturation with normal arterial oxygen saturation. We describe a family of three with Hb Cheverly in Sarawak General Hospital, Malaysia. It was discovered through incidental finding during hospital admission for unrelated complaints. Laboratory testing revealed abnormal haemoglobin detected at the C window of the high performance liquid chromatography. Subsequent DNA analysis detected replacement of thymidine by cytosine at the beta globin genes. Hb Cheverly may or may not have clinical significance as most of the patients live a normal life; however, it is crucial for us to make early diagnosis to prevent unnecessary extensive investigations for hypoxaemia detected via pulse oximetry, especially in the midst of COVID-19 pandemic.

Oxyhemoglobin concentrations do not support hemoglobinopathy in COVID-19

Based on computerized modeling studies, it has been postulated that the severe hypoxemia in COVID-19 may result from impaired oxygen carrying capacity on hemoglobin. Standard pulse oximetry may not detect hypoxemia resulting from hemoglobinopathy, therefore hemoglobin co-oximetry is needed to evaluate this divergence. In a clinical data analysis of a multicenter cohort of hospitalized patients with COVID-19, we found a minimal effect, less than 1%, on the correlation between oxyhemoglobin concentration and predicted oxygen saturation in the presence of COVID-19 infection. This effect is unlikely to explain the clinically significant hypoxia in COVID-19 patients.

A Case of Hb Aalborg (HBB: c.223G>C) with Chronic Obstructive Pulmonary Disease: A First Familial Presentation in Japan

The proband was a male in his seventies who came to our facility because of shortness of breath. He was not anemic but presented dissociation between oxygen saturation (SpO₂) and partial pressure of oxygen (PaO₂) by blood gas analysis, and also demonstrated hemoglobinopathy after measurement of Hb A_1c using high performance liquid chromatography (HPLC). Twenty-three percent of unknown hemoglobin (Hb) bands were detected. After sequencing the β-globin gene, we noted a missense mutation at codon 74 (GGC>CGC) (Gly→Arg) of the β-globin chain and he was diagnosed with Hb Aalborg (HBB: c.223G>C). One of the proband's siblings was diagnosed to have a low SpO₂ level and also diagnosed to carry Hb Aalborg; she was also mildly anemic. This is the first known familial case of Hb Aalborg in Japan. In addition to Hb Aalborg, our case had underlying chronic obstructive pulmonary disease (COPD). Herein we present this case as a rare addition to the hematological literature.

Hemoglobin Sunshine Seth: A Case Report of Low-Oxygen-Affinity Hemoglobinopathy

Pulse oximetry is routinely used in the newborn nursery for clinical monitoring and to detect critical congenital heart disease. The differential diagnoses for reduced peripheral oxygen saturation in an infant include congenital heart disease, respiratory distress syndrome, transient tachypnea of the newborn, persistent pulmonary hypertension of the newborn, meconium aspiration syndrome, pneumonia, pneumothorax, and sepsis. The diagnostic evaluation for neonatal hypoxemia can be invasive and expensive. When this evaluation is unrevealing, other interventions may be tried without clear benefit to the patient, including, but not limited to, supplemental oxygen. Therefore, it is important to consider alternative, albeit rare, diagnoses, including hemoglobinopathies with abnormal oxygen binding properties. Mutations in the structure of alpha- and beta-globin chains can alter the affinity of hemoglobin for oxygen, and changes in oxygen affinity may result in changes in the oxygen saturation detected by pulse oximetry. These changes may or may not be of clinical significance. This case report describes Hemoglobin Sunshine Seth, a rare low-oxygen-affinity hemoglobin variant presenting as reduced peripheral oxygen saturation in an otherwise well-appearing infant male.

A Japanese Family with the Unstable Hb Sydney (HBB: c.203T>C) Variant and Persistent Low Hemoglobin Oxygen Saturation

Patients with unstable hemoglobin (Hb), caused by a qualitative abnormality in α- and β-globin genes, are often asymptomatic or mildly symptomatic. It is often difficult to diagnose unstable Hb patients with only mild hemolysis or low oxygen saturation. We herein report a case of a family with an unstable Hb, specifically, Hb Sydney (HBB: c.203T>C), an abnormal β-globin chain. A 5-year-old boy was referred to our hospital for low percutaneous oxygen saturation (SpO₂) in the setting of bronchitis. During hospitalization, low SpO₂ persisted despite the improvement in respiratory distress symptoms. As he had mild hemolysis and splenomegaly, his disease was diagnosed to carry Hb Sydney based on gene analysis. His mother and brother also carried Hb Sydney. In this case, bronchial asthma had been treated, but unstable Hb was not assessed. Low SpO₂ may be tolerated and overlooked in cases of asthma and it took time to diagnose this patient. The present case suggests that unstable Hb should be considered in patients with bronchial asthma and prolonged low SpO₂.

Oxygenation during general anesthesia and thoracic surgery in a patient with Titusville low-oxygen affinity hemoglobin

The purpose of this case study is to describe the physiological characteristics of a patient with the low-oxygen affinity Titusville hemoglobin variant. A 46-yr-old man with exertional dyspnea was diagnosed with a mediastinal lymphadenopathy of unknown origin and, to obtain definitive diagnosis by biopsy, underwent endobronchial ultrasound-guided transbronchial needle aspirate under sedation and video-assisted thoracoscopy under general anesthesia. High inspired fraction of oxygen ( FIO2 ) was used to guarantee adequate oxygenation even during the one-lung ventilation needed for thoracoscopy. Following radial and pulmonary arterial catheterization, continuous mixed-venous oxygen saturation ( SVO2 ), cardiac output, oxygen delivery (DO₂), oxygen consumption (V̇o₂), and oxygen extraction ratio (ERO₂) were measured. Serial blood gas analyses were obtained at different FIO2 . Anesthesia and surgery were carried out safely. Data obtained during the clinical case were utilized to 1) construct an in vivo Titusville hemoglobin dissociation curve and 2) describe oxygen delivery and consumption of a human with Titusville mutation. Titusville hemoglobin showed relatively high P50 (i.e., 30 vs. normal of 27) and very low cooperativity (Hill coefficient of 1.45 vs. normal 2.27), which was compensated in our patient by increases in cardiac output, rather than by augmenting oxygen extraction.

Changes in biochemical tests in pregnancy and their clinical significance

Interpretation of laboratory investigations relies on reference intervals. Physiological changes in pregnancy may result in significant changes in normal values for many biochemical assays, and as such results may be misinterpreted as abnormal or mask a pathological state. The aims of this review are as follows: 1. To review the major physiological changes in biochemical tests in normal pregnancy. 2. To outline where these physiological changes are important in interpreting laboratory investigations in pregnancy. 3. To document the most common causes of abnormalities in biochemical tests in pregnancy, as well as important pregnancy-specific causes.

How I treat hypoxia in adults with hemoglobinopathies and hemolytic disorders

Hemoglobinopathies are caused by genetic mutations that result in abnormal hemoglobin molecules, resulting in hemolytic anemia. Chronic complications involving the lung parenchyma, vasculature, and cardiac function in hemoglobinopathies result in impaired gas exchange, resulting in tissue hypoxia. Hypoxia is defined as the deficiency in the amount of oxygen reaching the tissues of the body and is prevalent in patients with hemoglobinopathies, and its cause is often multifactorial. Chronic hypoxia in hemoglobinopathies is often a sign of disease severity and is associated with increased morbidity and mortality. Therefore, a thorough understanding of the pathophysiology of hypoxia in these disease processes is important in order to appropriately treat the underlying cause and prevent complications. In this article, we discuss management of hypoxia based on three different cases: sickle cell disease, β-thalassemia, and hereditary spherocytosis. These cases are used to review the current understanding of the disease pathophysiology, demonstrate the importance of a thorough clinical history and physical examination, explore diagnostic pathways, and review the current management.

Review article: Investigations and the pregnant woman in the emergency department - part 1: Laboratory investigations

Accurate assessment of the pregnant patient in the ED depends on knowledge of physiological changes in pregnancy, and how these changes may impact on pathology tests, appearance on point-of-care ultrasound and electrocardiography. In addition the emergency physician needs to be cognisant of disorders that are unique to or more common in pregnancy. Part 1 of this review addresses potential deviations in laboratory investigation reference intervals resulting from physiological alterations in pregnancy, and the important causes of abnormal laboratory results in pregnancy. Part 2 will address the role of point-of-care ultrasound in pregnancy, physiological changes that may affect interpretation of point-of-care ultrasound, physiological changes in electrocardiography, and the safety of radiological procedures in the pregnant patient.

Estimation of Achievable Oxygen Consumption Following Transfusion With Rejuvenated Red Blood Cells

Erythrocyte storage induces a nonphysiological increase in hemoglobin-oxygen affinity (quantified by low p50, the oxygen tension at 50% hemoglobin saturation), which can be restored through biochemical rejuvenation. The objective was to mathematically model the impact of transfusing up to 3 standard allogeneic units or rejuvenated units on oxygen delivery (DO₂) and oxygen consumption (VO₂). Oxygen dissociation curves were generated from additive solution-1 red blood cell (RBC) leukoreduced units (n = 7) before and after rejuvenation following manufacturer's instructions. Two of these units were used to prepare standard or rejuvenated donor RBC and added to samples of fresh whole blood. These admixtures were used to construct an in vitro transfusion model of postoperative anemia and determine a linear equation for calculating the sample p50, which was subsequently used to calculate DO₂ and VO₂ after simulated transfusions. Whole blood-packed red blood cell unit admixture p50s could be predicted from a linear model including the p50 of its components, the mass fraction of the transfused component, and interaction terms (R² = .99, P < 0.001). Transfusion with standard units slightly, but significantly, increased projected DO₂ compared with rejuvenated units (P = 0.03), but rejuvenated units markedly increased projected VO₂ (P = 0.03). Standard units did not significantly change VO₂ relative to pre-transfusion levels (P > 0.1). Using high-p50, rejuvenated RBC in simulated transfusions greatly improved projected VO₂, indicating the potential for increased end-organ oxygen availability compared with standard transfusion. Patient capacity to increase cardiac output after cardiac surgery may be limited. Transfusing high-p50 RBC in this setting may improve the perioperative care of these patients.

An unusual presentation of chronic cyanide toxicity from self-prescribed apricot kernel extract

Hypoxia under general anaesthesia is a potentially life-threatening condition. A seemingly well 67-year-old man appeared hypoxic with peripheral pulse oximetric measurement during routine anaesthesia. Postoperatively, the patient admitted to daily self-prescription of apricot kernel extract for a period of 5 years. Apricot kernel is a commonly taken extract used for a range of ailments, and is associated with cyanide toxicity, which was confirmed through blood analysis. Our explanation for the hypoxic measurement was the presence of free cyanide interfering with functioning of the peripheral pulse oximeter. On cessation of the apricot kernel extract, peripheral oxygen saturations returned to normal. Cardiac and respiratory causes together with rare haemoglobinopathies were excluded. This case illustrates how chronic dosing of complementary medicines can result in harmful toxicities, which may carry potential for serious consequences and how these chronic toxicities may present to physicians in atypical ways.

Hemoglobin Kansas as a Rare Cause of Cyanosis: A Case Report and Review of the Literature

Hemoglobin (Hb) Kansas is an inherited Hb variant with a low oxygen affinity that is associated with low oxygen saturation on pulse oximetry (SpO₂). It leads to asymptomatic cyanosis. Patients with Hb Kansas do not require any specific treatment and the prognosis is good. In patients with unexplained cyanosis, we should thus consider Hb variants, including Hb Kansas and avoid unnecessary investigations and managements. We herein report the case of 65-year-old woman with Hb Kansas and review five other cases (three lineages) that have been reported in Japan.

Pulse oximetry error in a patient with a Santa Ana haemoglobinopathy

A young man with a rare unstable haemoglobinopathy presented with a high fever, worsening shortness of breath and abdominal pain. At triage his pulse oximetry (SpO2) suggested that his blood oxygen saturation was 84% at room air. However, an arterial blood gas (ABG) oxygen saturation reading (SaO2) was 100%. The significant disparity between the two measurements demonstrates that using pulse oximetry in some unstable haemoglobinopathies may significantly underestimate the actual reading. This error is most probably due to the structural differences in the variant haemoglobin causing light to be absorbed at a different wavelength beyond the normal range of the oximeter. Haemoglobinopathies affect about 7% of the world's population and is often asymptomatic; so, there may be many more undiagnosed cases. Therefore, clinicians may confirm low SpO2 readings with an ABG and, where there is significant disparity with no obvious extrinsic cause, they should consider haemoglobinopathies.

Hb Grifton [α87(F8)His→Pro; HBA1: C.263A > C (or HBA2)] Causes Abnormal Pulse Oximetry Measurements

An asymptomatic toddler and his mother consistently demonstrated low transcutaneous pulse oximetry (SpO2) measurements, discordant with normal arterial blood gas analyses while breathing room air. Previous evaluations by medical teams were unable to identify an etiology of their perceived hypoxia. Further investigation revealed that the boy carried an abnormal variant, Hb Grifton or α87(F8)His→Pro; HBA1: c.263A > C (or HBA2), discovered on newborn screening, which was not suspected as the underlying cause of his abnormal pulse oximetry readings until an inpatient admission to our hospital for asymptomatic "hypoxia," where he was found to share these same characteristics with his mother. We showed that a difference in light absorption between the oxygenated Hb Grifton variant and oxygenated Hb A resulted in erroneous pulse oximetry values. This phenomenon has previously been reported in a handful of other variant Hbs. Astute clinical suspicion, in conjunction with laboratory testing leading to correct diagnoses of variant Hbs, may prevent expensive work-ups and unnecessary medical treatments for asymptomatic patients falsely presumed to be hypoxemic based on low pulse oximetry measurements.

Diagnosis and clinical presentation of hemoglobin Kirksey

More than 1000 hemoglobin (Hb) variants have been identified. Hb Kirksey, a rare Hb variant involving mutation at codon 94 of α2-globin, is associated with low oxygen affinity. To our knowledge, there is no case report on Hb Kirksey in the literature, and, accordingly, the clinical features of patients with Hb Kirksey are currently unknown. We report here the case of a neonate who presented with asymptomatic low oxygen saturation on pulse oximetry (SpO2 ) just after birth, together with clinical analysis of the sister and cousin. Based on the presentations, Hb Kirksey does not seem to be associated with clinical abnormalities. Discrepancy between SpO2 and partial pressure of arterial oxygen (PaO2 ) detected on arterial blood gas analysis provided a clue to the diagnosis. Hb variants should be suspected and arterial blood gases should be measured in pediatric cases of unexplained low SpO2 .

A novel haemoglobin variant mimicking cyanotic congenital heart disease

Screening for critical congenital heart defects in newborn babies can aid in early recognition, with the prospect of improved outcome. However, as this universal newborn screening is implemented, there will be an increasing number of false-positive results. In order to avoid multiple investigations and uncertainty, an haemoglobin (Hb) variant must be included in the differential diagnosis in otherwise well newborns with low oxygen saturation by pulse oximetry. We describe a novel fetal Hb variant (heterozygous γ-globin gene (HBG1) mutation in exon 2 c.202G>A (p.Val68Met)) identified in a newborn with positive pulse oximetry screening for congenital heart disease.