C.G. Fraser

Components of Variance of Some Plasma Constituents in Patients with Myocardial Infarction

Analytical, intra-individual, and inter-individual components of variance were estimated for eight plasma analytes in 20 patients who had myocardial infarction. Replicate analyses were performed on an average of 19·5 specimens obtained from each patient over a four-day period. Analytical variance was >25% of the total variance for sodium, chloride, and bicarbonate levels but ≤12% for potassium, urea, creatinine, calcium, and albumin. Sodium, bicarbonate, urea, and creatinine concentrations showed strong individuality while those of potassium, chloride, calcium, and albumin did not. Estimates of average intra-individual variation were larger than those previously documented; this is probably due to variation in sample collection, transport, and handling. Analytical goals were derived from intra-individual variation but it is not recommended that these be adopted in hospital laboratories.

A quality assurance programme for quantitative urine analyses

Summary Eighty‐six Australasian laboratories participated in an inter‐laboratory quality assurance programme for 10 urine analytes. Twelve liquid samples were prepared from commercial lyophilized urine control material and distributed in 3 batches of 4. Use of pre‐set acceptability limits for total laboratory error and target values facilitated timely feedback in graphic form. The samples had concentrations which were linearly related; this allowed simple calculation of overall imprecision and bias, graphic feedback of all submitted results, and comparison of performance between laboratories. A number of unsuitable and poor methods were identified. Particular attention must be paid, in future, to more widespread use of appropriate calibration and quality control materials, to avoidance of transcription and calculation errors, and to analysis of urine samples with elevated levels of analyte. Current laboratory performance can meet analytical goals for analyses of urine creatinine, phosphate, urate, and glucose but analysis of urine sodium, potassium, urea, calcium, osmolality, and proteins require significant improvement.

Goals for clinical biochemistry analytical imprecision: A graphic approach

&NA; Analytical performance standards for the imprecision of commonly requested clinical biochemistry tests are proposed in the form of goal graphs. The goals delineated in graphic form are a consensus of published performance standards. The graphs define acceptable and unacceptable performance standards for levels of analyte commonly encountered in clinical laboratory practice. The graphic approach allows a flexible presentation of goals that is easy to interpret. The disadvantage of goal graphs is their necessarily empirical foundation.

Analytical goals for quantitative urine analysis.

&NA; A regional survey of the performance of quantitative analysis of ten commonly requested urinary analytes was carried out in South Australia. Using the results achieved by the better laboratories as a basis, an empirical set of analytical goals for total laboratory error was derived; this is the first definition of such goals for quantitative urinary analysis. The goals are particularly for use in the assessment of laboratory performance in inter‐laboratory surveys.

Evaluation of precision using lyophilised quality control materials.

There has been a constant demand by users of quality control materials that such materials should be identical in appearance with specimens from patients (Anido, 1975). Lyophilisation procedures commonly used for preserving serum increase the turbidity because of insolubilisation of lipid constituents (Oncley et al., 1950). This turbidity may increase the absorbance of the control material and it causes a particular problem in the assay of enzymes by methods which are based upon the NADH/NAD+ reaction. Measurements at 340 nrn may be particularly affected, as turbidity can increase the initial high absorbance of NADH, and the resultant readings may be made at an imprecise aortion of the absorbance scale. We found that the within-run analytical precisions certain enzyme analyses on the Beckman System TR Enzyme Analyzer, notably aspartate and alanine aminotransferases (EC 2.6.1.1 and EC 2.6.1.2), were significantly inferior to those reported IyPassey et al. (1975) when a number of lyophiliscd quality control materials were used. In contrast, the malytical precision with fresh, clear, or Iipaemic serum from hospital patients was very similar to

An inter-laboratory quality-assurance survey of emergency clinical biochemistry tests

One hundred and thirteen Australian laboratories participated in a state-of-the-art quality-assurance survey of emergency clinical biochemistry tests. Two liquid-reconstituted lyophilised human-based serum samples, which had previously been analysed in the national general serum chemistry programme, were sent by air cargo, together with their own previously completed request forms, for analysis as emergency tests on a previously nominated date. The standard of performance of ten of the eleven most commonly performed tests was inferior to that obtained on a routine basis, as judged by the number of results outside present limits of total laboratory error from target values which had been previously set by reference laboratories. The standard of analytical performance achieved for emergency tests can and should be improved.

The Effect of Instrument Variables on Calculation Factors for Standardisation of Colorimetric Analyses

A number of colorimetric methods, particularly enzyme activity assays, are usually standardised using calculation factors based on the molar absorptivity of a principle reactant or product. Such methods are subject to long-term variation. The relationship between long-term variation in results and instrument variables affecting calculation factors has not been quantitated. In this study, we have shown that, on a centrifugal analyser having a within-run coefficient of variation of less than 1%, instrument variables affecting calculation factor alone could result in changes in results of up to 8·5% over 75 days. We therefore advocate daily use of a solution of potassium dichromate to monitor instrument variables that can independently affect calculation factors and within-run imprecision. This procedure is useful for maintaining long-term performance and for differentiating problems of instrumental or chemical origin.

Evaluation of a radiometric method for the determination of total and unsaturated iron binding capacities

The precise and accurate analysis ofiron binding capacity still poses a number of problems. A commercial kit (RESO-MAT, Mallinckrodt Australia Pty Ltd) for the determination of total and unsaturated iron binding capacities based on the use of Fe 59 as a transferrin saturant has heen evaluated and compared with a mechanized colorimetric method. The method was found to have acceptable precision and accuracy. The results obtained by the radiometric method compared well with those obtained using a colorimetric method. The radiometric test kit has a number of advantages over colorimetric methods in that haemolysis, lipaemia and icterus do not interfere, preparation of iron standards and calibration curves is not required, and minimal preparation and/or addition of reagents is necessary.

An inter-laboratory survey of qualitative urinalysis

Summary An inter‐laboratory survey of qualitative urinalysis was carried out in Australasia during 1981. Eighty‐one laboratories analysed 6 samples of urine distributed in 3 batches of 2 at regular bimonthly intervals, mostly with commercially available reagent strips. Fewer than 30% of laboratories performed any form of quality control for analytes other than pH. Results indicated that improvement in the analysis of urine bilirubin, protein, glucose, ketones and blood is required, and recommendations to improve standards are made.

Evaluation of a kit for the colorimetric determination of inorganic phosphate.

An evaluation of a colorimetric kit method for the determination of inorganic phosphate (Pierce Phosphorus Auto/Stat Kit) is described. The within-batch and between-batch precisions were shown to fulfil current criteria, and recovery experiments, linearity studies, analyses of quality control materials, and studies of possible interfering substances evidenced good accuracy. Comparison of the results obtained on samples from patients with those obtained by the vanadate/molybdate continuous-flow method showed that the test method had a comparative positive bias. The use of a calibration reference serum as standard is recommended. The kit method is technically simple, requiring no protein precipitation, and analyses can be performed rapidly.