Comparison of Creatinine, Urea, Ionized Calcium, and Bicarbonate Methods by 2 POC Systems and a Mainframe Chemistry Analyzer.

BACKGROUND: The i-STAT (iST) and GEM Premier ChemSTAT (ChmST) are point-of-care systems that measure electrolytes, metabolites, acid-base parameters, and hematocrit on blood. We compared results for creatinine, urea (blood urea nitrogen [BUN]), total carbon dioxide (tCo2), and ionized calcium (ion Ca) on blood by the ChmST and iST to Beckman DxC600 (DxC600) results for creatinine and urea on plasma and GEM Premier 5000 (GEM5K) results for ion Ca and tCo2 on blood. METHODS: 107 heparinized blood specimens were analyzed on the ChmST and iST systems, with plasma tested by DxC600 for creatinine and BUN and blood tested by GEM5K for ion Ca and tCo2. We evaluated the methods primarily by the mean and SD of the biases at clinically relevant concentrations. RESULTS: The correlations of ChmST and iST results on blood for creatinine, BUN, ion Ca, and tCo2 correlated to plasma by the DxC600 and to blood by the GEM5K were r ≥ 0.98 for all analytes except for ion Ca on the iST (r = 0.93). The mean and SD of biases were within clinically and analytically acceptable limits for all methods except for tCo2 on the ChmST, which measures bicarbonate with a bicarbonate-sensing electrode. Also, creatinine and BUN by the ChmST were less affected by icterus or hemolysis than were the DxC600 (icterus) and the iST (hemolysis). CONCLUSIONS: The ChmST and iST results on blood demonstrated strong correlations with each other and with the DxC600 results on plasma. We conclude the ChmST provides reliable results for whole blood creatinine, urea, ion Ca, and tCo2.

Progesterone receptor repression of prolactin/signal transducer and activator of transcription 5-mediated transcription of the beta-casein gene in mammary epithelial cells.

Prolactin (PRL) and glucocorticoids act synergistically to stimulate transcription of the beta-casein milk protein gene. Signal transducer and activator of transcription 5 (Stat5) mediates PRL-dependent trans-activation, and glucocorticoid potentiation occurs through cross talk between glucocorticoid receptor (GR) and Stat5 at the beta-casein promoter. In the mouse, progesterone withdrawal leads to terminal differentiation and secretory activation of the mammary gland at parturition, indicating progesterone's role in repressing milk protein gene expression during pregnancy. To investigate the mechanism of the inhibitory action of progesterone, experiments were performed with cell culture systems reconstituted to express progesterone receptor (PR), the PRL receptor/Stat5 signaling pathway, and GR, enabling evaluation of PR, GR, and Stat5 interactions at the beta-casein promoter. With COS-1, normal murine mammary gland, HC-11, and primary mammary epithelial cells, progestin-PR directly repressed the PRL receptor/Stat5a signaling pathway's mediation of PRL-induced beta-casein transcription. Progestin-PR also inhibited glucocorticoid-GR enhancement of PRL induced trans-activation of beta-casein. Inhibition depended on a functional PR DNA binding domain and specific PR-DNA interactions at the beta-casein promoter. Chromatin immunoprecipitation assays in HC-11 cells revealed recruitment of PR and Stat5a to the beta-casein promoter by progestin or PRL, respectively. Recruitment was disrupted by cotreatment with progestin and PRL, suggesting a mutual interference between activated PR and Stat5a. Without PRL, progestin-PR also recruited Stat5a to the beta-casein promoter, suggesting that recruitment of an unactivated form of Stat5a may contribute to inhibition of beta-casein by progesterone. These results define a negative cross talk between PR and Stat5a/GR that may contribute to the physiological role of progesterone to repress lactogenic hormone induction of the beta-casein gene in the mammary gland during pregnancy.

Effect of beef ingestion by humans on plasma concentrations of creatinine, urea, and cystatin C.

PURPOSE: The effect of eating meat on serum concentrations of creatinine has varied among previous reports, with some finding no effect and others finding 50-100% increases, which appears related to how the beef is cooked. For other analytes related to kidney function, urea is well known to increase following a protein meal, and the effect of eating meat on cystatin C concentrations has been studied once. METHODS: We had 32 participants eat a measured amount of cooked beef (5-6 or 10-12 oz; 142-170 or 284-340 g) and collected blood for measurements at 1 h before and immediately before eating beef, then at 1, 2, and 4 h after eating the beef. We measured creatinine using both alkaline picrate and enzymatic methods, cystatin C using a nephelometric immunoassay, and urea using an enzymatic method. RESULTS: For creatinine, both the picrate and enzymatic methods showed similar responses, with a peak average increases of 5.9 µmol/L (0.07 mg/dL) and 4.6 µmol/L (0.05 mg/dL), respectively, at 2 h. Cystatin C had a very slightly maximal decrease of -0.037 mg/L at 2 h. Urea had the largest change, increasing by 0.30 and 0.77 mmol/L at 2 and 4 h respectively. CONCLUSIONS: Healthy individuals were found to have minor increases in serum creatinine (~5 µmol/L) following the ingestion of 5/6 or 10/12 oz of fried beef. Cystatin C appears to decrease very slightly in some people after beef ingestion, possibly due either to circadian variation or to a hormonal effect of eating. We conclude that ingesting these amounts of fried beef has a small effect on plasma creatinine concentrations. Although these increases would likely not affect the diagnosis of a kidney impairment in this population or in those with kidney disease, eating meat before collecting blood for creatinine measurement should be avoided.

Quality Control Practices for Chemistry and Immunochemistry in a Cohort of 21 Large Academic Medical Centers.

OBJECTIVES: In the United States, minimum standards for quality control (QC) are specified in federal law under the Clinical Laboratory Improvement Amendment and its revisions. Beyond meeting this required standard, laboratories have flexibility to determine their overall QC program. METHODS: We surveyed chemistry and immunochemistry QC procedures at 21 clinical laboratories within leading academic medical centers to assess if standardized QC practices exist for chemistry and immunochemistry testing. RESULTS: We observed significant variation and unexpected similarities in practice across laboratories, including QC frequency, cutoffs, number of levels analyzed, and other features. CONCLUSIONS: This variation in practice indicates an opportunity exists to establish an evidence-based approach to QC that can be generalized across institutions.

The analytical change in plasma creatinine that constitutes a biologic/physiologic change.

PURPOSE: Accurate and precise measurements of creatinine are necessary to evaluate changes in kidney function related to a decreased glomerular filtration rate (GFR). When serial measurements of creatinine are monitored in an individual, it is useful to know what magnitude of an analytical change in creatinine indicates a true physiologic/biologic change in plasma creatinine that might warrant clinical intervention. METHODS: We compared results between three different methods for creatinine using large chemistry analyzers, two based on alkaline picrate (AP1 and AP2), and one based on dry-slide enzymatic conversion (ENZ). On each of three different segments or days of the study spaced 1-2months apart, we selected 10 different plasma samples having creatinine concentrations ranging from about 0.5mg/dL to 4.5mg/dL (44 to 400µmol/L). Each sample was analyzed in triplicate on each of two same-model analyzers at each institution, then from this data we determined the precision of each model of analyzer. The within-instrument precision of each analyzer was evaluated from the differences between the triplicate results on each sample by each analyzer (mean and SD of the differences). The between-instrument precision was evaluated as the differences between results on the same sample (1, 2, 3, etc.) analyzed on different analyzers of the same model (A and B). This between-analyzer precision data was used to determine both the range and mean±2SD of the differences that could be used to indicate that greater changes in creatinine concentrations would represent a biologic change. RESULTS: The within-instrument precision was best for the ENZ method in comparison to the two alkaline picrate rate methods. The between-instrument precision of the 90 consecutive measurements (30 samples×triplicate analyses) between the same-model analyzers were (mean and SD of differences in mg/dL): -0.018 and 0.029 (ENZ); 0.016 and 0.11 (AP1), and -0.058 and 0.071 (AP2). CONCLUSIONS: While all three of the creatinine methods studied had good precision, the ENZ method had the best precision, such that a change of 0.07mg/dL (6µmol/L) in serial creatinine concentrations up to 1.5mg/dL on a patient could indicate a biologic change had occurred. For the alkaline picrate methods, a measured change of creatinine of 0.23mg/dL for AP1 or 0.11mg/dL for AP2 would indicate that a physiologic change in serum/plasma creatinine has occurred. While a definite biologic change may simply represent daily variations, detecting a biologic change in creatinine more rapidly could impact the ability of creatinine to detect early and clinically significant changes in renal function.