Uninterpretable cerebrospinal fluid absorbance scans caused by antibiotic therapy

Background The revised national guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage (UK) provide an objective means of assessing cerebrospinal fluid samples to determine the risk of subarachnoid haemorrhage. The guidelines are intended for general use, but samples rendered uninterpretable due to the presence of the antibiotic doxycycline have been described. Here, further cases of antibiotic-based interference, and their implications, are presented. Methods An archival search of cerebrospinal fluid spectra performed at Hallands County Hospital Halmstad was performed for the years 2011 and 2016–2019 in an attempt to locate instances of interference. Each case of suspected interference was further investigated with in vitro reproduction experiments as a means of confirmation and assessment of potential clinical impact. Results A total of 10 cases of cerebrospinal fluid curve interference were discovered: six due to doxycycline, three due to metronidazole and one due to tetracycline. Interference caused by the tetracycline class was revealed through in vitro experimentation to cause an apparent decrease in the sample’s net bilirubin absorbance; the presence of xanthochromia on visual inspection was, however, conserved. Conclusions The problem of cerebrospinal fluid absorbance curve interference might be more common than previously suspected. Due to the potential net bilirubin absorbance-lowering effect of tetracyclines, the author recommends visual examination of cerebrospinal fluid samples in every case.

EXPRESS: Uninterpretable cerebrospinal fluid absorbance scans caused by antibiotic therapy

Background The revised national guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage (UK) provide an objective means of assessing cerebrospinal fluid (CSF) samples to determine risk of subarachnoid haemorrhage (SAH). The guidelines are intended for general use, but samples rendered uninterpretable due to the presence of the antibiotic doxycycline have been described. Here, further cases of antibiotic- based interference, and their implications, are presented. Methods An archival search of CSF spectra performed at Hallands County Hospital Halmstad was performed for the years 2011 and 2016- 2019 in an attempt to locate instances of interference. Each case of suspected interference was further investigated with in vitro reproduction experiments as a means of confirmation and assessment of potential clinical impact. Results A total of 10 cases of CSF curve interference were discovered: 6 due to doxycycline, 3 due to metronidazole and 1 due to tetracycline. Interference due to the tetracycline class was revealed through in vitro experimentation to cause an apparent decrease in the sample’s net bilirubin absorbance(NBA); the presence of xanthochromia on visual inspection was, however, conserved. Conclusions The problem of CSF absorbance curve interference might be more common than previously suspected. Due to the potential NBA- lowering effect of tetracyclines, the author recommends visual examination of CSF samples in every case.

Modeling the Optical Responses of Noble Metal Nanoparticles Subjected to Physicochemical Transformations in Physiological Environments: Aggregation, Dissolution and Oxidation

Herein, we study how optical properties of colloidal dispersions of noble metal nanoparticles (Au and Ag) are affected by processes such as aggregation and oxidative dissolution. The optical contributions of these processes to the extinction spectra in the UV-vis region are often overlapped, making difficult its interpretation. In this regard, modeling the UV-vis spectra (in particular absorbance curve, peaks position, intensity and full width at half maximum -FWHM) of each process separately offers a powerful tool to identify the transformation of NPs under relevant and complex scenarios, such as in biological media. The proper identification of these transformations is crucial to understand the biological effects of the NPs.

Metachromasy in clay dye systems: the adsorption of acridine orange by Na-beidellite

The adsorption of the metachromic dye acridine orange (AO) by Na-beidellite was investigated by visible spectroscopy. Different types of clay-AO association were identified from the appearance and location of absorption bands α or β. The colloidal properties were determined from curves of the absorbance vs. the degree of saturation. Three regions were identified in the absorbance curve. In the first region beidellite is peptized with small amounts of AO and the dye penetrates into the interlayer space where it undergoes metachromasy due to π interactions between the aromatic entity and the oxygen plane of the clay. With larger amounts of AO (second region), the clay flocculates due to the aggregation of the dye cations in the interparticle space of the flocs. In excess AO (third region), beidellite is gradually peptized, forming small tactoids with monomeric AO in the interlayer space and at the same time adsorbing dimeric and polymeric AO cationic species at the solid-liquid interface. Compared with the other smectites, AO shows the greatest tendency to undergo metachromasy in the presence of beidellite.

Analysis of Cholesterol in All Lipoprotein Classes by Single Vertical Ultracentrifugation of Fingerstick Blood and Controlled-Dispersion Flow Analysis

This new, highly sensitive analytical system, based on controlled dispersion of the flowing sample, gives a rapid, continuous, and direct analysis for cholesterol in all lipoprotein classes, separated by single vertical-spin density-gradient ultracentrifugation. In this Vertical Auto Profile-II fingerstick system, designated VAP-IIfs, a narrow-bore Teflon coil serves as the reactor with no segmentation of the analytical stream by air bubbles, in contrast to the Technicon AutoAnalyzer used in the VAP-I method. Concentrations of high-, low-, intermediate-, and very-low-density lipoprotein cholesterol and lipoprotein(a) cholesterol are determined by decomposing the spectrophotometric absorbance curve for the continuous analysis of the centrifuged sample, with use of software developed in this laboratory. Total cholesterol is determined from the total area under the absorbance curve. For assaying total cholesterol, the CV between aliquots within a rotor ranged from 1.35% to 3.15%; the CV between rotors was 2.45%. Because only 18 microL of sample is required, VAP-IIfs can be readily adapted to analysis for lipoprotein cholesterol profiles in capillary blood samples. Total cholesterol values by VAP-IIfs for fingerstick and venous samples from 23 subjects agreed well: slope = 1.01 (SD 0.03), intercept = -21 (SD 51) mg/L, Sy/x = 50 mg/L, and r = 0.992. Results by VAP-IIfs also correlated highly with results for duplicate samples analyzed at the Northwest Lipid Research Laboratories.

Quantum yields of the primary photoaquation reactions of octacyanomolybdic-(IV) acid and octacyanotungstic(IV) acid

The quantum yield of the primary photoaquation reaction of octacyano- molybdio(1V) acid and octacyanotungstic(IV) acid has been determined by direct estimation of the two products of the reaction, viz., a CN- ion and a red heptacyano-aquo complex. The CN- ion was estimated polarographically, the red photoproduct spectrophotometrically. Both the methods gave the same value of the quantum yield, which was about 0.88 for the molybdenum and 0.78 for the tungsten system. Photolysis was done at O�C. This and the fact that acidic conditions were maintained during the photolysis sufficiently stabilized the red species to reveal, if the time of irradiation was not too long, an isosbestic point where only two species, the red complex and the M(CN)84- ion, were in equilibrium. The quantum yield was determined subject to the condition that the absorbance curve of the photolysed solution passed through the isosbestic point and secondary reactions had not yet set in.

A Quality-Control Program Based on the Use of Desk-Top Digital Computer

Programs written for a relatively inexpensive desk-top computer are used to calculate the chemical concentration of any batch of unknowns from a flattened absorbance curve with up to five points produced by single- or dual-channel continuous-flow analyzers and other instrumentation. Any value beyond the limits of the curve is rejected. The programs are then used to evaluate a pooled control serum from previously programmed standard deviation data. The sequence of calculation is such that computation of patient samples stops if the control value lies outside these programmed limits. The system ensures that no patient sample is reported, or even calculated, unless its accompanying control was within acceptable statistical limits. Acceptance of the system by technologists has been outstanding.

Determination of Caffeine in Serum and Urine

The method of Axelrod and Reichenthal for the determination of caffeine in serum and urine was modified. The benzene used in the extraction of caffeine was shown to alter the spectral absorbance curve of this compound. A method based on the differential absorbance spectrums of caffeine and related compounds is described. Both methods exhibited satisfactory replication, recovery of added caffeine, and comparable serum levels of the drug.

A STATISTICAL APPROACH TO THE ANALYSIS OF INFRARED BAND PROFILES

A method is described for the quantitative description of the profile and asymmetry of an infrared absorption band, based on the computation of the second and third incomplete moments of the absorbance curve. Provision is included for differentiation between the intrinsic band asymmetry and that induced by instrumental factors dependent on the direction of scan. A program has been prepared for an I.B.M. 1620 computer to facilitate the calculation of the moments. This program also yields the incomplete fourth moments, the statistical kurtosis parameter ([Formula: see text]), and the Gauss–Cauchy index, though these quantities are not employed in the present investigation. Examples are given of the application of these computations to the analysis of the effect of the spectral slit width on the profiles of bands at 812.7 and 726.6 cm−1 respectively in the spectra of carbon disulphide solutions of perylene and anthracene, and of the effect of the amplifier time constant on the asymmetry of the band at 2234.4 cm−1 in the spectrum of p-chlorobenzonitrile in tetrachloroethylene solution.