Partial least-squares regression for routine analysis of urinary calculus composition with Fourier transform infrared analysis

Quantitative assessment of urinary calculus (renal stone) constituents by infrared analysis (IR) is hampered by the need of expert knowledge for spectrum interpretation. Our laboratory performed a computerized search of several libraries, containing 235 reference spectra from various mixtures with different proportions. Library search was followed by visual interpretation of band intensities for more precise semiquantitative determination of the composition. We tested partial least-squares (PLS) regression for the most frequently occurring compositions of urinary calculi. Using a constrained mixture design, we prepared various samples containing whewellite, weddellite, and carbonate apatite and used these as a calibration set for PLS regression. The value of PLS analysis was investigated by the assay of known artificial mixtures and selected patients' samples for which the semiquantitative compositions were determined by computerized library search followed by visual interpretation. Compared with that method, PLS analysis was superior with respect to accuracy and necessity of expert knowledge. Apart from some practical limitations in data-handling facilities, we believe that PLS regression offers a promising tool for routine quantification, not only for whewellite, weddellite, and carbonate apatite, but also for other compositions of the urinary calculus.

Partial least-squares regression for routine analysis of urinary calculus composition with Fourier transform infrared analysis

Quantitative assessment of urinary calculus (renal stone) constituents by infrared analysis (IR) is hampered by the need of expert knowledge for spectrum interpretation. Our laboratory performed a computerized search of several libraries, containing 235 reference spectra from various mixtures with different proportions. Library search was followed by visual interpretation of band intensities for more precise semiquantitative determination of the composition. We tested partial least-squares (PLS) regression for the most frequently occurring compositions of urinary calculi. Using a constrained mixture design, we prepared various samples containing whewellite, weddellite, and carbonate apatite and used these as a calibration set for PLS regression. The value of PLS analysis was investigated by the assay of known artificial mixtures and selected patients' samples for which the semiquantitative compositions were determined by computerized library search followed by visual interpretation. Compared with that method, PLS analysis was superior with respect to accuracy and necessity of expert knowledge. Apart from some practical limitations in data-handling facilities, we believe that PLS regression offers a promising tool for routine quantification, not only for whewellite, weddellite, and carbonate apatite, but also for other compositions of the urinary calculus.

Potential of descriptive linear discriminant analysis for studying clinical chemical and haematological data from persons with heterozygous sickle cell disease

To study the potential of multivariate classification methods in order to obtain more insight into abnormal laboratory data from patients with sickle cell disease, we investigated standard haematological and clinical chemical variables of 18 controls and 37 apparently healthy persons with heterozygous sickle cell disease (Hb AS), all women, using both univariate and multivariate classification methods. In the univariate method, those with Hb AS showed decreased serum log aspartate aminotransferase (log AST) activity, mean corpuscular volume and mean corpuscular haemoglobin (MCH) and increased sodium concentration. The multivariate method identified sodium, potassium, urea, uric acid, log AST, alanine aminotransferase and MCH as the variables that produced maximal separation between persons with Hb As and controls. It increased the 'non-error rate' for classification of persons with Hb AS by 16.4% compared with classification based on the variable, MCH, that produced maximal separation by the univariate method. The frequency distribution of percentage Hb S in the Hb AS group proved bimodal with maximal separation at 37.0% Hb S. The subgroup with 37.0% or less (n = 16) was considered to have concomitant heterozygous alpha-thalassaemia-2. In the univariate method the subgroup characterized by greater than 37.0% Hb S (n = 21) had increased serum sodium and uric acid concentrations, perhaps related to sickle cell nephropathy, whereas the subgroup with less than or equal to 37% Hb S did not. The multivariate method added information to the univariate method by additionally identifying abnormalities in serum potassium and urea concentrations in the former subgroup.(ABSTRACT TRUNCATED AT 250 WORDS)

Profiling of plasma cholesterol ester and triglyceride fatty acids as their methyl esters by capillary gas chromatography, preceded by a rapid aminopropyl-silica column chromatographic separation of lipid classes

A rapid procedure for the isolation of plasma cholesterol ester and triglyceride fractions with aminopropyl-silica columns, followed by analysis of their fatty acid compositions by capillary gas chromatography with flame ionization detection, is described. Within-series and long-term (six months) series-to-series precision were investigated. The isolation procedure caused minimal cross-over between the two lipid classes. Reference values for 57 apparently healthy Dutch adults were established and compared with data reported from other countries. Feeding of rats with four diets differing in their fatty acid compositions showed the relationship between the composition of the fatty acids in the diet and those esterified to cholesterol in plasma. The method is of potential usefulness to the establishment of the compliance of dietary interventions and basic dietary experiments.

Simultaneous capillary gas chromatographic profiling of medium-and long-chain fatty acid methyl esters with split injection. Correction for injection-related discrimination by the 'bracketing' method

Split injection-related discrimination can be a source of inaccuracy and imprecision in quantitative capillary gas chromatographic profiling methods for compounds with relatively big differences in boiling points, such as the methyl esters of medium- and long-chain fatty acids prepared from biological materials. We systematically investigated a standard containing equal masses of saturated fatty acid methyl esters, with chain lengths from C5 to C26, under different injection conditions, including injection temperature, sample volume and split ratio. Day-to-day performance was studied under one set of conditions. Normalized peak areas, reciprocal response factors, using either C17 or C23 as an internal standard, and 'bracketed' reciprocal response factors (peak area of each analyte divided by half the sum of the peak areas of two adjacent esters were calculated. In all experiments the bracketed reciprocal response factors were found to be closest to unity with the lowest coefficients of variation.

Detection of 3 beta-hydroxysteroid dehydrogenase deficiency in a newborn by means of urinary steroid analysis

A urinary steroid excretion pattern of a 3-wk-old newborn, suffering from 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) deficiency, has been produced, employing capillary gas chromatography and subsequent mass spectrometric identification of the various excreted steroids. The diagnosis could be established, apart from the clinical symptoms, on the basis of a grossly elevated excretion of 16-OH-DHEA and 16-OH-pregnenolone, combined with mass spectrometric identification of the following steroids: 17-OH-preganolone, pregnanetriol, pregnanolone, pregnenetriol and 17-OH-pregnenolone.

Detection of 3 beta-hydroxysteroid-dehydrogenase deficiency by urinary steroid profiling: solvolysis of urinary samples should be a necessary prerequisite

A urinary steroid profile from a patient with suspected 3 beta-HSD deficiency was prepared using capillary gas chromatography, employing only enzymatic deconjugation with Helix pomatia juice. In the chromatogram only very small peaks of dehydroepiandrosterone and 5-pregnenetriol were visible apart from other, for the diagnosis non-significant, peaks. However, after repeating the analysis including an additional solvolysis step, highly significant peaks of DHEA and 5-pregnenetriol became apparent, which suggests the necessity for a solvolysis step for a positive proof of 3 beta-HSD deficiency by urinary steroid profiling.

Diagnosis of cerebrotendinous xanthomatosis (CTX) and effect of chenodeoxycholic acid therapy by analysis of urine using capillary gas chromatography

By means of capillary gas chromatography urine samples of patients with cerebrotendinous xanthomatosis (CTX) were investigated before and during treatment by oral administration of chenodeoxycholic acid. The occurrence of various conjugated bile alcohols, presumably glucuronides, was demonstrated, the major compound being 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha, 23 xi, 25-pentol. In the bile acid fraction norcholic acid and hydroxycholic acid were shown to be present in considerable amounts. In this way the presence of CTX can be demonstrated conclusively. After chenodeoxycholic acid therapy the excretion of both abnormal bile acids as well as of bile alcohols rapidly decreased within a few weeks, showing the effectiveness of the treatment. By early discovery and subsequent therapy it may be possible to prevent the onset of the detrimental symptoms such as mental deficiency, caused by the accumulation of cholestanol and cholesterol in CTX patients.

The diagnosis of 21-hydroxylase deficiency in a prematurely born infant on the basis of the urinary steroid excretion pattern

The urine of a 6-day-old prematurely born female infant (birth weight 1060 g) suspected of having a 21-OH-deficiency showed no steroid abnormalities on capillary GLC analysis. Using GC-MS tetrahydrocortisone (THE) and also 3 alpha, 17 alpha-dihydroxy-5 beta-pregnane-20-one (17-OH-Polone) were absent, but two androstanetriolone peaks were observed. In the urine collected on day 9 THE was absent, but a large amount of 3 alpha, 11 beta-dihydroxy-5-alpha-androstane-17-one (11-HA) was found by GC-MS to be contaminated by a small amount of 17-OH-Polone. The next urine specimen collected on the 22nd day while the child received cortisol therapeutically showed the characteristic steroid profile for the diagnosis 21-OH deficiency, large peaks of 17-OH-Polone, pregnanetriol (P3) and 11-keto-pregnanetriol (11-keto-P3). Over the next few weeks two other compounds were found to have been excreted in relatively large amounts, 3 xi, 16 xi, 17 xi, 20 xi-pregnanetetrol (16-OH-P3) and surprisingly also a 21-hydroxylated compound, namely 3 xi, 20 alpha, 21-trihydroxy-5-pregnene. These same two compounds were also found in the urine of another infant with suspected 21-OH deficiency. The urinary steroid excretion patterns characteristic for 21-OH deficiency are dependent on the maturity and age of the infant. In the prematurely born infant androstanetriolones appear in the urine before 17-OH-Polone. The occurrence of these different steroid excretion patterns is tentatively explained.