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Biomedical subjects

C M Corns

Publications and source records attributed to C M Corns.

8 recordsLinked to original sources
PubMed1990

Interference by haemoglobin with the cresolphthalein complexone method for serum calcium measurement.

The spectral interference caused by haemoglobin in the calcium-cresolphthalein complexone reaction was investigated. The results show that the nature of the haemoglobin derivative in the reaction mixture influences the degree of interference; in turn, the derivative formed depends on the order in which the sample and reagents are added. Methods using a single, alkaline cresolphthalein complexone reagent are most seriously affected by haemolysis due to persistence of oxyhaemoglobin. If the sample is added to an acid cresolphthalein complexone reagent then acid haematin is formed, this being converted to a different derivative on the addition of alkali, producing less pronounced interference. The addition of the sample to a buffer, followed by addition of complexone, appears to offer a means to correct for moderate haemolysis in the sample.

Buffers↗
PubMed1987

Some observations on the nature of the calcium-cresolphthalein complexone reaction and its relevance to the clinical laboratory.

The reasons for the non-linearity of the standard curve for the calcium-cresolphthalein complexone reaction have been investigated. Calcium forms both 1:1 and 2:1 complexes with cresolphthalein complexone; at low calcium concentrations the 1:1 complex predominates and causes non-linearity. At high calcium concentrations the cresolphthalein complexone concentration becomes limiting, resulting in flattening of the calibration curve. It is recommended that two-point calibration of the assay be performed using a low calcium standard rather than setting on the baseline.

Calcium↗
PubMed1987

A new colorimetric method for the measurement of serum calcium using a zinc-zincon indicator.

A new method is described for the measurement of serum calcium. Calcium in the sample displaces zinc from an EGTA complex, the zinc then forming a blue-coloured complex with a zincon indicator. The method is rapid, sensitive and linear; it may be applied directly to serum and is readily automated. No compound tested gave rise to any interference at physiological concentration, although excessive haemolysis leads to low results being obtained. To avoid interference from endogenous zinc a serum blank is required for each sample; this also avoids errors introduced by turbidity of the sample. The results obtained correlate well with atomic absorption spectroscopy (r = 0.935, y = 1.12x-0.28, n = 68).

Azo Compounds↗
PubMed1986

Evaluation of strategy for testing thyroid function applied to hypothyroidism.

A strategy for testing thyroid function with discretionary assay of thyroid stimulating hormone (TSH) following initial measurement of total plasma thyroxine (tT4) was retrospectively evaluated in relation to the diagnosis of primary hypothyroidism. Over a two year period 14 641 tT4 assays were done and 6887 TSH assays, of which 29% were initiated in the laboratory. The percentage of raised TSH values (over 5 mU/1) was similar to those for clinician and pathologist initiated requests (23.2% and 23.6%). Some TSH requests (1620) were cancelled; when 212 of these were subsequently analysed the TSH value was raised in 5.7% The incidence of raised TSH values in 188 patients with a tT4 below 100 nmol/1 (7.8 micrograms/100 ml), in whom TSH was not requested, was 5.3% Most of these raised TSH results could be readily explained by information available to the requesting clinician but not given on the request form.

Adult↗
PubMed1983

Infrared analysis of renal calculi: a comparison with conventional techniques.

The analysis of renal calculi is an oft-neglected corner of clinical biochemistry. This study compares results obtained by the conventional qualitative methods with results from quantitative and infrared methods and also investigates the role of x-ray diffraction analysis. Infrared spectroscopy, using a KBr disc technique, was found to be the single most useful method, being fast, simple to learn, using little sample, and in general permitting positive identification of most of the components found in renal calculi. A major advantage is that this method has approximately equal sensitivity for oxalate and phosphate, unlike the wet chemical methods. Infrared analysis is also useful in identifying the spurious materials sometimes submitted as renal calculi. X-ray diffraction analysis is not a technique that is routinely available, but it does provide information not given by other methods, eg, distinguishing Ca(COO)2 . H2O from Ca(COO)2 . 2H2O. For complete analysis a combination of methods was adopted; carbonate is tested for using a microchemical technique, calcium, magnesium, and phosphate are quantitated by routine methods, and infrared analysis is used to detect oxalate and organic components. It must be emphasised that any method is only as good as the sample used, and different areas of the calculus must be analysed separately if useful results are to be obtained.

Carbonates↗