A low-expression-class methicillin-resistant Staphylococcus aureus strain (strain 9302-2) was sent to 207 laboratories as part of the bacteriology component of the Laboratory Proficiency Testing Program of Ontario. An incorrect (susceptible) result was reported by 16 of 76 (21%) of laboratories that used the National Committee for Clinical Laboratory standards disk test, whereas 1 of 104 laboratories that used other methods reported an incorrect result (P < 0.05). Experiments showed discrepancies in the disk test results given by Mueller-Hinton agars from three manufacturers. We advise that laboratories should use a low expression-class methicillin-resistant S. aureus isolate as a control for the National Committee for Clinical Laboratory Standards disk test.

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The role of disulfide cross-linked proteins as template for thrombin generation might be of great interest. I agree with Dr. Lipinski that this phenomenon might condition an increased thrombin generation in diabetes. One may hypothesize that increased amounts of disulfide groups might be generated in diabetic plasma by oxidative stress (2). Perhaps the oxidative stress, which has been reported to be increased in both cardiovascular and diabetic patients, might be the link between disulfide cross-linked proteins and thrombin generation. In my opinion, the finding of the macromolecular protein complex may open a new interesting area of research with important therapeutic implication. Discrepant Results in INRTesting Dear Sir, We are writing to augment the data recently published by Bader eta!. (1) where they evaluated a new synthetic prothrombin time (PT) reagent, Innovin™ (Baxter Diagnostics Inc., Deerfield, Illinois). In their evaluation, the authors note that at higher International Normalized Ratio (INR) values, some slightly higher INR results were observed with Innovin rM compared to a human placental thromboplastin. As part of a province-wide proficiency testing program, regular monitoring of PT results has taken place in Ontario. Within Ontario, Canada, 277 out of 295 laboratories report PT results as an INR (frequently in conjunction with aPT report in seconds). Many reagents and instruments are in use in Ontario. Increasingly, more laboratories are

An analysis of the results of a compulsory proficiency testing programme in immunohaematology is presented. Error rates have been calculated for the determination of ABO and Rh(D) groups, the direct antiglobulin test and antibody detection according to defined criteria. The introduction of proficiency testing has been associated with alterations in error rates for some determinations. An educational programme introduced for laboratories with poor performance has proved effective in improving their results in the proficiency testing programme.

Proficiency testing results provide data for interlaboratory comparisons. The Laboratory Proficiency Testing Program of Ontario, Canada, has tested platelet counting for a decade and other hematology parameters for 15 years. Despite the fact that all testing programs are compromised by the type of testing material used, for platelet count testing, conclusions are possible. The data indicate that most laboratories in Ontario have greater difficulty performing reproducible platelet counting as compared with other components of hematologic cytometry. A major contributor to this shortfall is the method used by the laboratory. It was not a surprise that manual counting had a high coefficient of variation. Unexpectedly, the semiautomated methods used in the mid-1980s also displayed a high coefficient of variation.