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The results of examinations carried out in 37 clinical laboratories in Bulgaria which participated in the interlaboratory quality assurance check are discussed. The check included 202 laboratories from 5 countries members of the Council of Mutual Economic Aid and covers the examinations of chlorine, sodium, potassium, calcium, urea, creatinine, total protein, cholesterol, glucose, inorganic phosphorus. The results are assessed by the "normative standard deviation" which differs from the "absolute quality index" used in the national external laboratory quality assurance check. The results of the Bulgarian laboratories are better in the examinations of glucose, urea, cholesterol and inorganic phosphorus. The analytical variations in protein, sodium and chlorine equal those of the other participants while the results of calcium, potassium and creatinine show greater variations. The interlaboratory variations of the results obtained by the different analytical methods are discussed. The results of the examinations of calcium and potassium are least acceptable.

The method of the within-the-laboratory quality assurance check of the casual and systematic mistakes in the analytical process is presented. The results of the control serums are evaluated by the combined Shewart-cusum check card which is suitable for both casual and systematic mistakes while the classical check card controls the casual mistakes only. The method was used for evaluation of the analytical quality of the results determined by the automatic analyzer "RA 1000 Technicon". The general assessment of the combined method is that the systematic mistakes found are very often of no medical importance but in any case they are an "useful" information for the laboratory specialists in their efforts to provide a reliable laboratory information.