Evaluation of the methods used for carboxyhemoglobin analysis in postmortem blood

Forensic utility of carboxyhemoglobin levels in postmortem spleen specimens in South Korea

In order to determine whether CO poisoning was the definitive cause of death, the concentration of carboxyhemoglobin (COHb) in spleen specimens was analyzed using a gas chromatography-thermal conductivity detector. 125 cases of forensic autopsy reports containing COHb analysis requests were analyzed and subdivided into two groups, improbable and highly probable of CO intoxication. In the first group which consists of 100 cases, the results of COHb analysis were negative, and the circumstances of death, as well as the postmortem findings could not validate the exposure to CO. In the second group which consists of 25 cases, the results of COHb were positive, and both postmortem findings and circumstances of death confirmed the exposure to CO. In the cases of indoors and vehicle fires or those including the use of briquettes, COHb levels reached 43.1-97.5 %, whereas in individuals without any feature of CO poisoning had COHb level high as 29.8 %. However, certain cases without any connection to fire nor CO exposure also contained significant amount of CO based on post-mortem analysis. This study focuses on cases without any relationship to fire or CO and proves that COHb levels below 30 % may be considered as a contributing factor to but not exclusively as the cause of death.

Correlation between Carboxyhemoglobin Levels Measured by Blood Gas Analysis and by Multiwave Pulse Oximetry

Carbon monoxide (CO) poisoning is difficult to diagnose owing to its nonspecific symptoms. Multiwave pulse oximetry can be used to quickly screen patients for CO poisoning. However, few studies have analyzed patients with CO poisoning who presented to the emergency department (ED). The primary aim of our study was to determine the correlation between COHb levels measured in blood gas analysis and COHb levels measured in multiwave pulse oximetry. Secondary aims were the sensitivity and specificity of the COHb level cutoff value using multiwave pulse oximetry to predict a 25% COHb level in blood gas analysis. This single-center retrospective observational study included patients with CO poisoning who visited the ED of a university-affiliated hospital in Seoul, Korea between July 2021 and June 2023. COHb poisoning was determined using blood gas analysis and multiwave pulse oximetry. The correlation of COHb levels between the two tests was evaluated using correlation analysis. The area under the receiver operating characteristic curve (AUC) of multiwave pulse oximetry was calculated to predict COHb levels from the blood gas analysis. The optimal cutoff values, sensitivity, and specificity of COHb were determined. A total of 224 patients who had COHb levels measured using both multiwave pulse oximetry and blood gas analysis were included in the analysis. In the correlation analysis, COHb showed a high positive correlation with COHb measured using blood gas analysis (Spearman correlation coefficient = 0.86, p < 0.001). The AUC of COHb measured by multiwave pulse oximetry to predict 25% of the COHb level (which can be an indication of hyperbaric oxygen treatment) measured by blood gas analysis was 0.916. When the COHb levels measured with multiwave pulse oximetry were 20% the sensitivity was 81% and the specificity was 83%, and when the COHb levels were 25% the sensitivity was 50% and the specificity was 95%. The COHb value measured using multiwave pulse oximetry blood gas analysis showed a high correlation. However, additional research using large-scale studies is required for validation.

Thoracic cavity fluid as an alternative specimen for carboxyhaemoglobin measurement in post-mortem toxicology

Post-mortem blood is most frequently used for the measurement of carboxyhaemoglobin (COHb) in post-mortem forensic cases, when investigating suspected inhalation of carbon monoxide (CO). However, in many post-mortem cases (especially severe burns and charring deaths), adequate blood specimens are not always available for toxicological analyses. Here, the availability of an alternative specimen for COHb analysis is required. This study investigated the suitability of thoracic cavity fluid (TCF) as an alternative specimen for the measurement of COHb. TCF and comparative blood samples from fifteen potential CO toxicity cases were collected into green-top tubes (containing lithium heparin) and analysed immediately after collection using a validated method on the ABL825 FLEX Radiometer CO-oximeter. Pearson's correlation coefficient indicated a strong positive relationship between the two specimens (r = 0.975, n = 10, p < 0.001). A statistical agreement between COHb concentrations from blood and TCF was demonstrated using the Bland-Altman plot, with a slight bias of 1.54 % when blood was taken as the standard. This study found that TCF would be a suitable alternative to blood for the measurement of COHb using the ABL825 FLEX blood gas analyser.

Comparative Evaluation of Carboxyhemoglobin Quantification in Postmortem Whole Blood by CO-Oximetry and Headspace Gas Chromatography with Flame Ionization Detection and Atom Absorption Spectrophotometry

A comparative evaluation of two methods used for carboxyhemoglobin (COHb) determination in postmortem whole blood was performed: carbon monoxide (CO)-oximetry measuring at 128 wavelengths and headspace gas chromatography with flame ionization detection (HS-GC--FID) where CO was determined after catalytic reduction of CO to CH4 and Fe was determined by atom absorption spectrophotometry (AAS, 248.3 nm). An aliquot of 100 µL whole blood was loaded into the CO-oximetry module. In the HS-GC--FID analysis, to 1.0 mL of whole blood, 3.0 mL of saponin solution was added, mixed and centrifuged. To 20 mL HS vials, 400 µL of the supernatant was added and the vials were immediately sealed. One milliliter of potassium hexacyanoferrat (III) solution was added through the HS septum and mixed. The samples were incubated at 70°C for 5 min. CO was separated using He as carrier gas and a CP-Molsieve 5 Å PLOT capillary column. Fe was determined using 400 µL of the saponin supernatant diluted to 10 mL by water. During a period of ∼3 years, 124 postmortem whole blood samples were analyzed. Bland-Altman method comparison showed satisfactory agreement and no significant bias between the methods for the whole saturation range (5 to 85% COHb). Five samples, all with %COHb >40, showed deviations of more than 10% COHb in absolute terms. One sample, in the lower COHb range <10%, was false negative on the CO-oximetry method. The between-assay accuracy, reported as bias, at 60% COHb was -0.8% and -9.0%, and precision, reported as relative standard deviation, was 1.6% and 7.7%, for the CO-oximetry and HS-GC--FID-AAS methods, respectively. Both methods obtained satisfactory results in proficiency testing rounds, with z-scores <±2 (n = 11). This study showed that the CO-oximetry method based on the 128-wavelength principle and the HS-GC--FID-AAS method are comparable and satisfactory for %COHb determination in postmortem whole blood.

Analyses of physical factors that contribute to the blood carboxyhemoglobin saturation in autopsy cases of house fire fatalities

The authors analyzed data from forensic autopsies of 75 patients who died as a result of house fires to clarify the physical factors that affect blood carboxyhemoglobin (COHb) saturation. Blood COHb saturation levels were significantly lower in patients who survived in the hospital. No significant differences were found in the blood COHb saturation levels between patients who died immediately at the scene and those who were pronounced dead at the receiving hospital without heartbeat being restored. The COHb saturation levels were significantly different among the groups of patients classified by the amount of soot. Although age, coronary artery stenosis, and blood alcohol concentration did not significantly affect blood COHb saturation, on comparing patients who died in the same fire, lower COHb saturation was observed in two patients, one with severe coronary artery stenosis and other with severe alcohol intoxication. To accurately interpret blood COHb saturation during forensic autopsy, the heartbeat status (present or absent) at the time of the rescue and the amount of soot in the trachea must be determined. Low levels of COHb saturation may be observed in fatalities with severe coronary atherosclerosis or severe alcohol intoxication.

Diffusion of Carbon Monoxide and Hydrogen Cyanide to Muscles and Blood-An Experimental Study

Postmortem carbon monoxide (CO) and hydrogen cyanide (HCN) diffusion under ambient conditions was assessed in a human cadaver model. The main objective of this study was to determine whether the postmortem diffusion of HCN and CO greatly affected the determination of HCN, carboxyhemoglobin (COHb), and carboxymyoglobin (COMb). Layered samples of blood, musculocutaneous, and muscular specimens were collected from the adult cadavers and placed in the tight chambers designed for the purpose of this experiment. The specimens were treated with CO and HCN for 24 h. COHb and COMb were determined using headspace gas chromatography (GC) with an O-FID detector while the HCN values were assessed using a GC headspace with an NPD detector. It was shown that the skin substantially limited the diffusion of CO which penetrated the superficial layers of the muscle very slightly, all the while not affecting the blood level of COHb in the 4.5 cm layer of the muscle located underneath. There were no differences regarding the CO diffusion between superficially charred and thermally coagulated compared to that observed in intact integuments. In addition, the cutaneous sample deprived of the adipose layer was not shown to be a barrier to the moderate diffusion of CO into the blood layer below. HCN was found to easily diffuse from the skin to the blood vessels (vein specimens), and partial charring and thermocoagulation of the superficial muscular layer favored the diffusion of cyanides into the tissues. Similarly to CO, HCN diffusion to the blood and muscles was greatly limited by the adipose layer.

Comparison of Spectrophotometric Methods for the Determination of Carboxyhemoglobin in Postmortem Blood

Carbon monoxide (CO) poisoning presents an interesting challenge for postmortem toxicology laboratories. The discontinuation of the CO-oximeter manufactured by Instrumentation Laboratories has left many forensic laboratories without this simple but reliable choice for the analysis of CO in blood. A comparable alternative that is quick and simple is analysis using a standard ultraviolet-visible spectrophotometer, which offers sufficient precision and accuracy for the measurement of percentage carboxyhemoglobin (%COHb) in postmortem blood. The hurdle for laboratories then becomes the selection of an appropriate spectrophotometric method since a variety of procedures have been published over the years. Four methods were evaluated based on literature findings and/or the appropriateness for postmortem testing. These methods are based on (i) relating %COHb to the ratio of COHb and Hb absorbance of a two-component system (two wavelengths), (ii) the multicomponent analysis of all hemoglobin species, (iii) the multicomponent analysis of a two-component system, and (iv) derivative spectroscopy. While all four methods performed similarly in terms of typical validation requirements, the ability to more effectively handle decomposed samples and the ease of sample preparation afforded (v) the multicomponent analysis of a two-component system-the most suitable for routine postmortem testing.

Assessment of carboxyhemoglobin content in the blood with high accuracy: wavelength range optimization for nonlinear curve fitting of optical spectra

The impact of carbon monoxide (CO) gas on the human organism is very dangerous. The affinity of CO to hemoglobin is considerably higher than that of oxygen. Thus, the interaction of CO with the blood results in a higher content of carboxyhemoglobin (HbCO) in red blood cells (RBCs) and correspondingly in tissue hypoxia. The disruption in the organism depends on the HbCO content in the blood. To assess any complications in the body at a given moment due to CO exposure and predict future consequences, it is necessary to measure the dynamics of hemoglobin derivative concentrations simultaneously. However, measuring HbCO and other derivatives in RBCs without hemolysis accurately is complicated due to the strong intercollinearity between the molar absorptivities of hemoglobin derivatives and superposition of absorption and scattering spectra. In the present study, to quantitatively assess the contents of the hemoglobin derivatives in the blood after exposure to CO, improved accuracy is achieved by optimizing the wavelength range used for the nonlinear curve fitting of optical spectra. Experimental spectra were measured in the wavelength range Δλ=500−700nm. For each experimental curve, it was established the value of optimal interval Δλopt for which the correlation coefficient between experimental data and corresponding points of the theoretical fitting curve was the maximum in the wavelength range Δλtyp=535−580nm, which contains the typical absorption peaks for HbO2, Hb, and HbCO. The concentrations obtained based on such fitting curves were considered to be highly accurate. The quantitative assessment enabled the determination of theHbCO nonlinear increase with the time of CO exposure in the in vitro experiment and the study of the dynamics of hemoglobin derivative transformations during blood incubation.

New strategy for carbon monoxide poisoning diagnosis: Carboxyhemoglobin (COHb) vs Total Blood Carbon Monoxide (TBCO)

Diagnosis of carbon monoxide (CO) poisonings has always been a challenging task due to the susceptibility to alterations of the optical state and degradation of blood samples during sampling, transport and storage, which highly affects the analysis with spectrophotometric methods. Methodological improvements are then required urgently because of increased reports of cases with discrepancies between results of the measured biomarker carboxyhemoglobin (COHb) and reported symptoms. Total blood CO (TBCO) measured chromatographically was thus proposed in a previous study as alternative biomarker to COHb. This approach was investigated in this study by comparing the two biomarkers and assessing the effects of various storage parameters (temperature, preservative, time, tube headspace (HS) volume, initial saturation level, freeze- and thaw- and reopening-cycles) over a period of one month. Results show that while for TBCO, concentrations are relatively stable over the observation period regardless of parameters such as temperature, time and HS volume, for COHb, concentrations are altered significantly during storage. Therefore, the use of TBCO as alternative biomarker for CO poisonings has been proposed, since it provides more valid results and is more stable even under non-optimal storage conditions. Additionally, it can be used to predict COHb in cases where sample degradation hinders optical measurement. Furthermore, a correction formula for COHb and TBCO is provided to be used in laboratories or circumstances where optimal storage or analysis is not possible, to obtain more accurate results.

The relationship between the intramuscular bleeding of the tongue and cause of death

Intramuscular bleeding of the tongue (ImBT) is occasionally found during post mortem examination. Despite its frequent reports, its cause has not yet been clarified. In this study, forensic autopsy data of 799 cadavers were examined and the relationship between ImBT and cause of death was investigated. A total of 74 cases showed ImBT (16 of 66 cases of fire fatality, 17 of 108 cases of drowning, 23 of 74 cases of asphyxiation, and 18 of 551 cases of other causes of death). The frequency of bleeding was significantly greater in cases with causes of death including fire fatality, drowning, and asphyxiation compared to those with other causes of death (p < 0.01). Among asphyxiation cases, ImBT was confirmed in two of five cases of typical hanging, three of 16 cases of atypical hanging, six of six cases of ligature strangulation, two of two cases of manual strangulation, eight of 38 cases of airway obstruction, and two of seven cases of oxygen deficiency. Among fire fatalities, the carboxyhemoglobin (CO-Hb) concentration of cases with ImBT was significantly lower than that in cases without ImBT (p < 0.01). In addition, the frequency of bleeding was significantly higher (p < 0.05) in cases where the blood cyanide concentration was 0.05 ppm or less. These observations suggested that ImBT during fire fatality occurs in a manner similar to that of ligature or manual strangulation, in which the flames cause the contraction and decrease in elasticity of the skin. Past reports indicated that bleeding frequency in cases of drowning did not significantly differ from that in cases with other causes of death. However, our cases showed a statistically higher incidence of bleeding compared to that in the other causes of death (p < 0.01). These results suggested that ImBT is a characteristic finding in cases of asphyxia and is an important evaluation for the diagnosis of death. When the relationship between ImBT and petechial hemorrhage was examined in three of the causes of death, no significant difference was observed between fire fatality and asphyxiation, but drowning was significantly different (p < 0.05). In cases without ImBT, the secretion of noradrenaline and adrenaline was significantly higher (p < 0.01). This finding suggests that it is unlikely that excessive secretion of catecholamine causes ImBT.

Turn-on and Turn-off Fluorescent Probes for Carbon Monoxide Detection and Blood Carboxyhemoglobin Determination

Water-soluble, carbazole-based two-photon excitable fluorescent probes MPVC-I ("turn-on") and MPVC-II ("turn-off") are rationally designed and synthesized for the selective monitoring of carbon monoxide (CO). Both probes can effectively measure carboxyhemoglobin (HbCO) in the blood of the animals exposed to a CO dose as low as 100 ppm for 10 min. The palladium catalyzed azidocarbonylation reaction was optimized to improve the sensing efficiency.

Carbon monoxide analysis method in human blood by Airtight Gas Syringe - Gas Chromatography - Mass Spectrometry (AGS-GC-MS): Relevance for postmortem poisoning diagnosis

Carbon monoxide is one of the most abundant toxic air pollutants. Symptoms of a CO intoxication are non-specific, leading to a high number of misdiagnosed CO poisoning cases that are missing in the disease statistics. The chemical nature of the molecule makes it difficult to detect for long periods and at low levels, thus requiring a very accurate and sensitive method. Current methods capable of accurate and sensitive analyses are available, however an inconsistency between results and symptoms are frequently reported. Therefore, an improved method for the analysis of carbon monoxide in blood and in the headspace (HS) of the sampling tube with the use of Airtight Gas Syringe - Gas Chromatography - Mass Spectrometry (AGS-GC-MS) is hereby presented and validated, for CO concentrations in a range of 10-200 nmol/mL HS (2-40 μmol/mL blood). Analytical LOQ is found at 0.9 nmol/mL HS (0.18 μmol/mL blood) and LOD at 0.1 nmol/mL gas. Application to intoxicated samples from autopsies and comparison to previously published methods show that this method is more appropriate, since performed under fully controlled conditions. Results show higher CO concentrations compared to previous approaches, indicating that results might have been underestimating the true blood CO burden. Therefore, this approach has the potential to help reduce the misdiagnosed cases and the gap between measurement and diagnosis of CO poisonings.

An accurate method for microanalysis of carbon monoxide in putrid postmortem blood by head-space gas chromatography-mass spectrometry (HS/GC/MS)

Carbon monoxide (CO) may be the cause of more than half the fatal poisonings reported in many countries, with some of these cases under-reported or misdiagnosed by medical professionals. Therefore, an accurate and reliable analytical method to measure blood carboxyhemoglobin level (COHb%), in the 1% to lethal range, is essential for correct diagnosis. Herein a method was established, i.e. head-space gas chromatography-mass spectrometry (HS/GC/MS) that has numerous advantages over other techniques, such as UV spectrometry, for determination of COHb%. There was a linear relationship (R(2)=0. 9995) between the peak area for CO and the COHb% in blood. Using a molecular sieve-packed column, CO levels in the air down to 0.01% and COHb% levels in small blood samples down to 0.2% could be quantitated rapidly and accurately. Furthermore, this method showed good reproducibility with a relative standard deviation for COHb% of <1%. Therefore, this technique provides an accurate and reliable method for determining CO and COHb% levels and may prove useful for investigation of deaths potentially related to CO exposure.

Accuracy and usefulness of the AVOXimeter 4000 as routine analysis of carboxyhemoglobin

The measurement of blood carboxyhemoglobin (CO-Hb) is important to determine the cause of death. The AVOXimeter 4000 (AVOX), a portable CO-oximeter, has the advantages of a low purchase price and operating cost, ease of operation, and rapid results. Little information is available on the usefulness of AVOX in the forensic sample, and the previous study investigated only six samples. Therefore, in this study, we confirmed the usefulness of the AVOX through a comparison of its results with data previously obtained using the double wavelength spectrophotometric method in autopsies. Regression analysis was performed between CO-Hb levels measured by the AVOX and those measured by the conventional double wavelength spectrophotometric method in postmortem blood samples: a significant correlation was observed. This study suggests the usefulness of the AVOX to analyze postmortem blood, and the AVOX is suitable for routine forensic analysis and can be applied at the crime scene.