Clinical chemistry
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Carboxyhemoglobin determined in neonatal blood with a CO-oximeter unaffected by fetal oxyhemoglobin.
Measurements of carboxyhemoglobin (COHb) for clinical purposes are routinely made with CO-oximeters. However, fetal hemoglobin (HbF) interferes with this spectrophotometric method. The manufacturer (Ciba Corning Diagnostics) of a new CO-oximeter (CCD 270) claims that COHb measurements with this instrument are insignificantly affected by HbF. ⋯ Linear regression analysis of HbF and COHb measurements (n = 68) showed significant correlation (P < 0.0001) between the two factors for the older CCD 2500 CO-oximeter (R2 = 0.56), but not for the CCD 270 (R2 = 0.06) or GC (R2 = 0.02). Bilirubin concentrations, which affected COHb measurements with CCD 2500, did not significantly affect CCD 270 measurements. We conclude that COHb measurements with CCD 270 CO-oximeter are not affected by HbF or bilirubin concentrations.
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Case Reports
Excess serum osmolality gap after ingestion of methanol: a methodology-associated phenomenon?
A patient intentionally ingested an unknown amount of methanol and was admitted to the hospital 6 h later. On admission, the methanol concentration in blood was estimated as approximately of 134 mmol/L, based on the calculation of the osmolal gap. Intravenous ethanol administration and hemodialysis were promptly started. ⋯ Initially, we used gas chromatography with split-mode injection of pretreated serum samples; however, methanol concentrations turned out to be significantly lower than expected, based on calculated osmolal gap values. Because no explanation for the excess serum osmolal gap was apparent, we reanalyzed samples, using head-space gas chromatography. The methanol concentrations measured were significantly higher and osmolal gap values were no longer excessive.
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We evaluated a new analyzer designed for point-of-care testing of blood gases, sodium, potassium, ionized calcium, and hematocrit. The Gem Premier (Mallinckrodt) system has two components: the analyzer and a disposable cartridge. Analysis takes place in the cartridge, which contains the electrochemical sensors, the calibrants, the reagents, the sampling stylus, and the waste container. ⋯ With aqueous control materials, total imprecision (CV) was: pH, 0.10-0.18%; PCO2, 3.16-5.78%; PO2, 2.92-4.85%; sodium, 0.82-1.44%; potassium, 1.35-1.48%; ionized calcium, 0.75-1.45%; and hematocrit, 1.13-1.83%. Accuracy of the system was assessed by split-sample comparison with the Radiometer ABL 330 blood gas analyzer for pH and blood gases, the Nova Stat Profile 5 for whole-blood electrolyte and hematocrit analysis, and the IL Phoenix for plasma electrolyte analysis. After outlier correction, regression statistics were excellent for all analytes except sodium, which demonstrated Sy[x values between 1.80 and 2.30 mmol/L and 0.85 < or = r < 0.90.
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Comparative Study
Measurement of carboxyhemoglobin and total hemoglobin by five specialized spectrophotometers (CO-oximeters) in comparison with reference methods.
We measured total hemoglobin (CtHb) and carboxyhemoglobin (COHb) in 100 patients' blood samples by using five specialized spectrophotometers (CO-oximeters)--IL 482 CO-Oximeter, Corning 2500 CO-oximeter, Radiometer OSM 3 Hemoximeter, Corning 270 CO-oximeter, and the AVL 912 CO-Oxylite--and compared the results with those obtained with the manual cyanmethemoglobin method and a gas-chromatographic (GC) method, respectively. For the CtHb measurements, the differences between the cyanmethemoglobin method and the CO-oximeters were not clinically important for any model. ⋯ We conclude that all five CO-oximeters compared favorably with the reference methods for CtHb and for high concentrations of COHb. However, the inaccuracy of CO-oximeters for low-concentration (< or = 2.5%) COHb measurements may make these instruments unsuitable for some applications.
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When cyanide poisoning is treated with a methemoglobin-forming agent, oxidative metabolism is protected at the expense of the oxygen capacity of the blood. The affinity of methemoglobin for CN- is high enough to compete with cytochrome oxidase, which protects the latter from becoming blocked, but all hemoglobin used for this purpose is lost for the transport of oxygen. ⋯ After we had developed a multiwavelength spectrophotometric method for this purpose, we studied the feasibility of using a modified commercial six-wavelength hemoglobin photometer (Radiometer OSM3) for easy and rapid analysis of methemoglobin and methemoglobin cyanide in small samples of blood. All conditions appeared to be fulfilled for the construction of a practical multiwavelength photometer for reliably monitoring methemoglobin therapy in patients with cyanide poisoning, even in the presence of carboxyhemoglobin, as often occurs in fire victims.