In vitro interference by acetaminophen, aspirin, and metamizole in serum measurements of glucose, urea, and creatinine.

OBJECTIVE: Here we aimed to investigate the in vitro effects of three analgesic-antipyretic drugs frequently used in clinical practice in Mexico - acetaminophen (AAP), aspirin (ASA) and metamizole (MMZ) - on serum measurements of glucose, urea, and creatinine. DESIGN AND METHODS: Each analyte was measured in a base-serum pool spiked with the drugs at subtherapeutic, therapeutic, and toxic doses. Serum glucose and urea were measured using the hexokinase/G-6PDH and urease/GLDH kinetic assays, respectively. Serum creatinine (SCr) was measured with a Jaffe procedure based on the alkaline-picrate reaction and with an enzymatic dry-chemistry system. Measurements were carried out in IL-Monarch and Vitros DT60-II analyzers, respectively. Data were analyzed by the difference-paired interference test and by ANOVA. RESULTS: By the kinetic Jaffe/Monarch procedure, we found positive interference by the drugs on the SCr measurements and by only ASA for urea measurement. For creatinine measurements, the total errors (TEs) were 22-51%, 18-105%, and 15-26% for AAP, ASA, and MMZ respectively, while for urea measurement the TE was 16-21% for ASA. A negative interference by MMZ on SCr (TE=-47%), but no-interference for AAP or ASA, were found via the enzymatic/DT60-II system. CONCLUSIONS: In vitro positive interference induced by AAP, ASA, and MMZ (via the alkaline-picrate reaction), or negative interference by MMZ (via a dry-chemistry system), on the SCr measurements highlights the importance of investigating all possible sources of variation that may alter the accuracy of the laboratory tests, in order to provide useful results for making medical decisions for optimal patient care.

Frequency of Salmonella and Listeria monocytogenes in five commercial brands of chicken eggs using a combined method of enrichment and nested-PCR.

Eggs or egg-based foods, either raw or undercooked, have been identified as vehicles of Salmonella outbreaks. The low numbers of Salmonella organisms in eggs makes it difficult to detect them in frequency studies. The nested-PCR (n-PCR) technique shows more sensitivity and specificity than bacteriological culture methods (BCMs). A preenrichment method followed by enrichment and n-PCR is a good alternative for the investigation of Salmonella and Listeria monocytogenes in eggs. A total of 2,650 chicken eggs representing five commercial brands were purchased from 10 grocery stores. Ten eggs of each brand were combined in order to obtain 265 pooled samples (53 per brand). The shells and yolks of 100 pooled samples were analyzed for Salmonella, while the shells of 65 pooled samples were analyzed for L. monocytogenes, using BCM and a combined method of enrichment and n-PCR (CM-n-PCR). Sixteen eggshell pooled samples tested positive for Salmonella by CM-n-PCR, compared with only two by BCM. Three egg yolk pooled samples tested positive for this pathogen by CM-n-PCR; none tested positive by BCM. Three eggshell pooled samples tested positive for L. monocytogenes by CM-n-PCR and none by BCM. In Mexico, as in other countries, official methods for detection of Salmonella and L. monocytogenes in foods are based on standard bacteriological culture techniques. The inclusion of more sensitive methods such as the one used in the present investigation would increase the probability of detecting positive samples, particularly in those foods in which a very low number of cells is expected.