Measurement of iohexol by capillary electrophoresis: minimizing practical problems encountered.

Iohexol is a non-ionic contrast agent, which has been widely described in recent literature as an accurate marker for the measurement of glomerular filtration rate (GFR). Our aim was to establish a capillary electrophoresis assay, based on a previously described method, that had adequate reproducibility to be used as part of a clinical trial. In this paper, we examine the practical aspects, pitfalls and steps we took to achieve a precise and reproducible assay. To minimize laboratory variation, we examined properties such as the use of an internal standard in a capillary electrophoresis separation, alternative deproteinization methods for serum, the most suitable matrix for the dilution of standards and the implementation of suitable quality control material to ensure that run-to-run variability was minimized. The optimized capillary electrophoretic assay of iohexol was found to be robust, with over 860 runs from the one capillary over a 9-month period. Excluding capital costs of the instrument, the consumable cost of the assay is less than A$0.25 per test, with a run time of 5.25 min and a coefficient of variation (CV) of 4.3% at 80 mg/L. The GFR, calculated from the plasma clearance, had a reproducibility of 5.47%.

Lupus anticoagulant in the elderly may be associated with both quinine and quinidine usage.

Thirty-one patients aged over 60 yrs and with lupus anticoagulant (LA) were reviewed for their drug intake. Twenty-three (73%) were taking cinchona alkaloids, 10 (32%) quinine for night cramps, 11 (35%) quinidine for cardiac arrhythmia and 2 (6%) were taking both. These frequencies of drugs usage differed significantly from age and sex matched controls (p < 0.001). Five patients had features suggestive of the antiphospholipid syndrome. Repeat testing showed persistent LA activity in all but 2 of 5 patients in whom the relevant drug had been ceased. This is the first description of a possible causal association between LA and quinine therapy.

Automation of the Kaolin Clotting Time.

An automated Kaolin Clotting Time (KCT) has been developed to simplify screening for the Lupus Anticoagulant (LA). The assay is performed on the ACL300 Research coagulation analyser, but may be modified for other centrifugal analysers. Automation of the KCT allows up to 17 delta KCT (delta KCT) screens (Gibson J, Starling E, Date L et al. Simplified screening procedure for detecting lupus inhibitor. J Clin Pathol 1988; 44: 226-31) or 2 full Exner curves (Exner T, Rickard KA, Kronenberg H. A sensitive test demonstrating lupus anticoagulant and its behavioural patterns. Br J Haematol 1978; 40: 143-51) to be performed in one test cycle. An automated and manual delta KCT screen was performed on 17 patients with a previously diagnosed LA, 41 hospital patients having routine coagulation studies and 37 blood donors. In addition, 11 patients on full-dose heparin and 12 patients with stable warfarin anticoagulation were tested. The correlation between the automated delta KCT and the manual delta KCT was 0.958 (p less than 0.001). A full Exner curve was performed on 5 of the patients with a LA and 1 blood donor which demonstrated that the automated KCT produced results entirely comparable with the manual method. The automated KCT is a quick, inexpensive approach to screening patients for the presence of LA.