Search

To assess the affect of haemolysis on routine photometric methods used by participants in the Irish External Quality Assessment Scheme for Clinical Biochemistry (IEQAS) a sample was distributed with a supplied diluent containing haemoglobin. A sample of the same batch had previously been circulated as a normal distribution. Many analytes/methods were affected by the haemolysis. The range of values reported for each analyte was as follows. Albumin 34-48 g/L (baseline 37 g/L). Calcium 2.16-2.68 mmol/L (baseline 2.34 mmol/L). Urate 90-470 mumol/L (baseline 195 mumol/L). Creatinine 55-161 mumol/L (baseline 140 mumol/L). Glucose 4.1-5.6 mmol/L (baseline 4.8 mmol/L). Bilirubin 14-60 mumol/L (baseline 36 mumol/L). Urea 3.4-7.3 mmol/L (baseline 3.8 mmol/L). Iron 17.9-55.0 mumol/L (baseline 26.8 mumol/L). Inorganic phosphorus 0.22-2.41 mmol/L (baseline 1.59 mmol/L). Cholesterol 3.0-5.9 mmol/L (baseline 4.1 mmol/L). In some situations the use of an appropriate blank may solve the problem, but it must be remembered that interference caused by haemoglobin may be more complex than merely spectral.

Bilirubin is oxidized to biliverdin by 1.0 mmol/L potassium ferricyanide in the presence of caffeine. The absorbance decline at 480 nm with blanking at 660 nm is proportional to bilirubin concentration. The assay is linear up to 1000 mumol/L and is suitable for the measurement of bilirubin in adult and neonatal patients. The assay is accurate and precise and is not significantly affected by haemolysis up to 5.0 g/L haemoglobin. Reagents and calibration are stable for at least 3 months.

The Technicon SMAC system was adapted to function with much smaller volumes of plasma than those used in standard procedures. With only minimal operator-entered changes to the 7.6 computer program, and simple modifications of the glucose and alkaline phosphatase channels, the SMAC analyser performed equally well when the plasma volume was decreased from 235 microliter sequentially down through 176 microliter, 142 microliter, and 105 microliter. The basic principle employed was to maintain a constant flow rate of diluted sample plus diluent with decreasing sample size. The instrument proved to have the capability of operating successfully on all channels with lower signals than those encountered with the unmodified system.