Interpreting sulfhemoglobin and methemoglobin in patients with cyanosis: An overview of patients with M-hemoglobin variants.

INTRODUCTION: Methemoglobin (MetHb) and sulfhemoglobin (SHb) measurements are useful in the evaluation of cyanosis. When one or both values are elevated, additional analysis is important to establish the etiology of the disorder. Methemoglobinemia occurs from acquired or hereditary causes with diverse treatment considerations, while true sulfhemoglobinemia is only acquired and treatment is restricted to toxin removal. Some toxic exposures can result in a dual increase in MetHb and SHb. Hereditary conditions, such as M-Hemoglobin variants (M-Hbs), can result in increased MetHb and/or SHb values but are clinically compensated and do not require treatment if they are cyanotic but otherwise clinically well. METHODS: Herein, we report 53 hemoglobin variant cases that have associated MetHb and SHb levels measured by an adapted Evelyn-Malloy laboratory assay method. RESULTS: Our data indicate M-Hbs cause variable patterns of MetHb and SHb elevation in a fairly reproducible pattern for the particular variant. In particular, α globin chain M-Hbs can mimic acquired sulfhemoglobinemia due to an isolated increased SHb value. CONCLUSION: If the patient appears clinically well other than cyanosis, M-Hbs should be considered early in the evaluation process to differentiate from acquired conditions to avoid unnecessary testing and treatment regimens and prompt genetic counseling.

Failing blood gas measurement due to methemoglobin forming hemoglobin variants: a case report and review of the literature.

INTRODUCTION: We present a case of an arterial blood gas sample analysis from a 33-year old woman where no oximetry results could be obtained using the Radiometer ABL800 FLEX device. Clinical history of this patient learned that she was carrier of a methemoglobin forming hemoglobin variant type Hyde Park (HbM Hyde Park) and raised the question whether or not this variant could be the cause of the errors obtained during analysis. MATERIALS AND METHODS: A literature search was performed, focusing on methemoglobin forming hemoglobin variants and their influence on oxygenation measurements. An overview of the currently described methemoglobin forming hemoglobin variants is also included. RESULTS AND DISCUSSION: In the presence of dyshemoglobins such as methemoglobin, techniques used to obtain parameters that reflect the patient oxygenation status, such as pulse oximetry and CO-oximetry can be influenced. In these cases, CO-oximetry is the preferred technique because it can compensate for this, in contrast to pulse oximetry. In case of the presence of methemoglobin originating from a hemoglobin variant, it is possible that CO-oximetry data cannot be calculated because the absorbance spectrum of this methemoglobin can differ from regular methemoglobin. Moreover, pulse oximetry devices are actually prone to erroneous results since pulse oximetry data will be calculated in these cases, but unreliable and should be avoided. CONCLUSION: Methemoglobin forming hemoglobin variants are rare genetic mutations. However, they can possibly interfere with the calculation of CO-oximetry values. In these cases, pulse oximetry data should be avoided because they could lead to incorrect medical decisions.

Metahemoglobinemia. Causa de cianosis en el niño / Methemoglobinemia. Cause of cyanosis in the child

La metahemoglobina (MHb) es una forma de hemoglobina que presenta el hierro del grupo hem en estado férrico (oxidado), minimizando su captación y transporte de oxígeno. La metahemoglobinemia se produce cuando, por causa genética, los mecanismos redox son insuficientes, o bien si, de forma adquirida, la cantidad de sustancias oxidantes superan los mecanismos redox del hematíe. Presentamos dos casos clínicos, el primero de los cuales es un lactante que, tras una exposición prolongada a una sustancia oxidante (parche de lidocaína-prilocaína [EMLA®]), presenta cianosis con repercusión hemodinámica, niveles elevados de MHb y respuesta al azul de metileno. El segundo caso es el de una niña con cianosis desde el nacimiento, en la que se constató un déficit de citocromo b5 reductasa. Ante un paciente cianótico sin causa infecciosa, respiratoria o cardiológica conocida, y sin respuesta a la oxigenoterapia, es necesario descartar la metahemoglobinemia (AU)

The methemoglobin (MHb) is a form of hemoglobin which shows iron “hem” in ferric (oxidized), while minimizing its uptake and oxygen transport. Methemoglobinemia occurs when by the genetic cause the redox mechanisms are insufficient or if acquired by the amount of oxidizing substances which exceed the redox mechanism of red blood cells. We present two clinical cases, the first being an infant after prolonged exposure to an oxidizing substance (EMLA® patch) presented with hemodynamic cyanosis, high levels of MHb and response to methylene blue. The second patient was a girl with cyanosis since birth in which there was a deficit of cytochrome b5 reductase. Before acyanotic patient without infectious, respiratory and cardiovascular known cause and without a response to oxygen therapy it is necessary to exclude methemoglobinemia (AU)

Determination of the amounts and oxidation states of hemoglobins M Boston and M Saskatoon in single erythrocytes by infrared microspectroscopy.

The reduced abnormal subunits of two M-type hemoglobins, Boston (His alpha 58-->Tyr) and Saskatoon (His beta 63-->Tyr), have been determined in the presence of normal human hemoglobin A by measurement of C-O stretch bands in infrared spectra of carbon monoxide complexes. Use of an infrared microscope coupled to a Fourier transform infrared spectrometer of high sensitivity permitted measurements to be made on as small a hemoglobin mixture as is contained in a single erythrocyte. The abnormal subunits of both Hbs M exhibit bands near 1970 cm-1 compared with bands near 1951 cm-1 for the normal subunits. The increase in 1970 cm-1 band intensity upon erythrocyte reduction with dithionite provided a measure of the extent of abnormal subunit oxidation; in cell suspensions about 60% of the abnormal subunits of Hb M Boston and 80% for Hb M Saskatoon remained reduced. The amount of Hb present as abnormal Hb averaged about 25% for Hb M Boston cells and about 50% for Hb M Saskatoon cells. However, the ratio of Hb M to Hb A in individual cells varied markedly, with the ratio expected to decrease as the cell ages. These results demonstrate the unique utility of infrared microspectroscopy for the study of differences in abnormal Hb status among individual erythrocytes.

[Oxygen-binding properties of blood in hemoglobinosis M Boston detected in the USSR for the first time]. / Kislorodsviazyvaiushchie svoistva krovi pri gemoglobinoze M-Boston, vpervye vyiavlennom v SSSR.

Hemoglobin M-Boston comprising 30% of the total blood Hb was detected in two members of a Russian family. The stages of its identification were described. An analysis was made of probands' whole blood oxy-Hb dissociation curves. At pO2 = 100 mm Hg oxygenation of Hb M-Boston beta-chains was 44% only, while mutant alpha-chains were completely oxidated. Despite a significant decrease in arterial blood oxygen content arteriovenous variation by O2 content at pO2 differential from 100 to 40 mm Hg is within the normal level due to various directions of changes in P50 and Hill's coefficient of probands' whole blood. The authors consider that pronounced cyanosis in Hb M-Boston carriers is not the consequence of tissue hypoxia but is caused by a higher content of nonfunctioning Hb M-Boston that changes the blood color.

Fast atom bombardment mass spectrometric analysis of haemoglobin variants: use of V-8 protease in the identification of Hb M Hyde Park and Hb San Jose.

The characterization of two human haemoglobin variants, Hb M Hyde Park and Hb San José, by fast atom bombardment mass spectrometry is reported. The identification of the site and nature of the amino acid substitution was performed by analysis of the peptide mixture generated by proteolytic digestion of the variant beta-globin chains with V-8 protease. The use of this protease was instrumental in the unambiguous identification of the replaced residues because the tryptic map alone was unable to unequivocally locate the modification. Spectra obtained were easily interpreted and the characterization of Hb M Hyde Park (beta, 92 Hys leads to Tyr) and Hb San José (beta 7 Glu leads to Gly) was accomplished essentially by the same procedure already described for the tryptic map. These results are suggestive of alternative approaches in haemoglobin variants characterization using different proteolytic enzymes when tryptic data alone do not lead to unambiguous results.

[Hereditary cyanosis caused by the presence of abnormal hemoglobin M in the blood: its detection, identification and properties]. / Nasledstvennye ysianozy, obuslovlennye prisutstviem v krovi anomal'nykh Hb gruppy M: vyiavlenie, identifikatsiia, svoistva.

A total of 17 cases of anomalous hemoglobin M (Hb M) were detected among subjects of varying nationalities in different regions of the USSR. The methods used for identification of Hb M Saskatoon, Hb M Boston, Hb M Iwate, Hb M Hyde Park have been described, among them--electron paramagnetic resonance. Spectral characteristics, electrophoretic mobility of these Hb in pH gradient, reaction with cyanides, thermal stability, in vitro reduction with methemoglobin reductase, isolated from donor's red blood cells, have been investigated. The functional parameters (log P50 and n) have been determined for hemolysates containing anomalous hemoglobin, as well as for chromatographically pure fractions of anomalous hemoglobins. The importance of the proper diagnosis of hemoglobinosis M has been stressed.

Molecular pathology of hemoglobin M Saskatoon disease.

Absorption spectra of erythrocyte hemolysate from a normal subject, the Hemoglobin (Hb1) M Saskatoon patient and the Hb M Boston patients were investigated. Difference spectrum between the hemolysate from either freshly obtained or 37 degrees C-incubated blood of the Hb M Saskatoon patient and that of the normal blood suggested that about 50% of the abnormal chain were in the ferrous state in the patient's blood. In contrast, no abnormal chain containing the ferrous heme was detected in the hemolysate from the fresh blood of the Hb M Boston patient. Resonance Raman (RR) studies indicated that methemoglobin (metHb) M Saskatoon with a weak Fe-tyrosinate interaction contained the six-coordinate heme like normal metHb A whereas metHb M Boston had the five-coordinate heme. Studies on effects of pH on absorption and RR spectra of these three hemoglobins suggested that the coordinated tyrosinate in the abnormal chain of Hb M Saskatoon was dissociated at pH 5.0. This unique heme structure of Hb M Saskatoon may relate to the susceptibility for the reduction by erythrocyte methemoglobin reductases, which is responsible for mild cyanosis of Hb M Saskatoon disease.

Mutant fetal hemoglobin causing cyanosis in a newborn.

A well but cyanotic newborn was found to have a mutant gamma-globin chain, leading to a functionally abnormal fetal hemoglobin. A single amino acid substitution was found in a site consistent with known adult M hemoglobins. This patient showed no clinical evidence of cyanosis at 5 weeks of age as gamma-chain synthesis was replaced by beta-chain synthesis. A sibling born 20 months later was also cyanotic and the same mutant hemoglobin was found.

A case of a newborn infant with Hb M Iwate.

Hemoglobin of a newborn infant who was suspected to hereditarily have Hb M Iwate was examined. The infant hemolysate was separated into five fractions by column chromatography on Amberlite CG-50, and two of these fractions showed absorption spectra corresponding with that of Hb M Iwate. Five bands were found after the isoelectric focusing of the hemolysate, and two of these bands were brown. The two Hb M fractions obtained by column chromatography was focused to the positions of the brown bands. One of these Hbs M corresponded with Hb M Iwate (alpha M2 beta 2) from an adult carrier of this trait, but the other was not found in adult hemolysates. The latter species of Hb M was shown to be composed of the abnormal alpha chain and the normal gamma chain (alpha M2 gamma 2) by chain analysis, and was assumed to be specific for infants. A quantitative estimation of the hemoglobins in the infant hemolysate showed that there was no difference between the relative quantities of the fetal and adult forms of Hb M Iwate.

alpha Chain and gamma chain abnormal hemoglobins in newborn babies: structural and genetic aspects.

Structural studies and quantitative analyses were conducted on the hemoglobin of 55 newborn babies. Seven alpha chain variants (G-Philadelphia, Montgomery, Inkster, I-Philadelphia, Matsue-Oki, Winnipeg, and O-Indonesia) were present in 26 heterozygous newborns (17 black, eight Caucasian, and one Indonesian). The relative amount of the alpha X containing abnormal Hb F of the Hb G-Philadelphia and Hb Winnipeg babies was less than observed in heterozygous adults, which may indicate a decreased rate of assembly of the alpha X-gamma dimer over that of the alpha X-beta dimer. Of the 29 newborns with gamma chain variants, 16 were Caucasian babies; of these 15 had a Hb A gamma F-Hull heterozygosity and one a Hb G gamma F-Marietta heterozygosity. Six black babies were heterozygous for Hb A gamma F-Texas-I and six for Hb G gamma F-Port Royal. One Japanese baby had a heterozygosity for A gamma F-Iwata and a second was heterozygous for A gamma TF-Yamaguchi. Quantitative analyses of the isolated normal Hb Fo as well as an evaluation of the relative amounts of the Hb Fx in the red cell lysates gave data useful for a speculation of the genetic condition in each of these babies. It was concluded that the babies with the Hbs F-Texas-I, F-Iwata, F-Hull, and F-Marietta were simple heterozygotes with either the G gamma x A gamma/G gamma x A gamma X or the G gamma x A gamma/G gamma X x A gamma genic arrangement. The babies with Hb F-Port Royal had a G gamma x G gamma X/G gamma x A gamma arrangement, which may result from a (to be determined) gene conversion. The newborn baby with Hb F-Yamaguchi has the G gamma x A gamma x/A gamma T-X.-. genic arrangement, suggesting the presence of three distinctly different gamma chain genes of which one, the A gamma T-X gene, produces an A gamma chain (with threonyl at position gamma 75 and an Asn at position gamma 80) at a level usually seen for G gamma rather than A gamma chains. These studies were greatly facilitated by the use of high pressure liquid chromatographic methods.