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BUTHELEZI, ERNEST P., MARIA-TERÉ SA VAN DER MERWE, PETER N. LÖ NNROTH, I. PETER GRAY, AND NIGEL J. CROWTHER. Ethnic differences in the responsiveness of adipocyte lipolytic activity to insulin. Obes Res. 2000;8:171-178. Objective: The goal of this study was to quantify differences in lipid metabolism and insulin sensitivity in black and white subjects to explain ethnic clinicopathological differences in type 2 diabetes. Research Methods and Procedures:The in vitro lipolytic activity of adipocytes isolated from obese black and white women was measured in the presence of insulin and isoproterenol. Insulin resistance was assessed in vivo using the euglycemic hyperinsulinemic clamp technique. Results: Fasting plasma levels of insulin and nonesterified fatty acid (NEFA) in black and white women were 67 Ϯ 5 pM vs. 152 Ϯ 20 pM (p Ͻ 0.01) and 863 Ϯ 93 M vs. 412 Ϯ 34 M (p Ͻ 0.01), respectively. Euglycemic hyperinsulinemic clamp studies showed that obese black subjects were more insulin-resistant than their white counterparts (glucose infusion rates: 1.3 Ϯ 0.2 vs. 2.2 Ϯ 0.3 mg/kg per min; p Ͻ 0.05). Isolated adipocytes from white women were more responsive to insulin than those from black women with 0.7 nM insulin causing a 55 Ϯ 4% inhibition of isoproterenol-stimulated lipolysis compared with 27 Ϯ 10% in black women (p Ͻ 0.05). Discussion: The low responsiveness of adipocyte lipolytic activity to insulin in black women in the presence of a relative insulinopenia may account for the high plasma NEFA levels seen in these women, which may, in turn, account for their higher in vivo insulin resistance. High NEFA levels may also contribute to the low insulin secretory activity observed in the obese black females. These data suggest that the pathogenesis of insulin resistance and type 2 diabetes within the black obese community is strongly influenced by their adipocyte metabolism.

Background: Delay in serum separation from red blood cells in samples collected from most primary healthcare facilities and transported to a laboratory for analysis is of great concern. Standard guidelines state that serum or plasma should be separated from cells within 2 hours of collection. The aim was to determine effects of delayed sample separation on measured biochemical analytes. The objective was to store blood samples in primary collection tubes at 20-25°C post venesection, then separate, and analyse samples of selected analytes. Methods: Multiple sample tubes of whole blood were collected from one of the authors volunteer, and subjected to time delays in centrifugation. The baseline serum was separated from red blood cells within 30 minutes of post venesection to allow adequate coagulation. Twenty analytes were studied using 2 analytical platforms. Percentage variation and standard error method were used to evaluate time-dependent variability in analytes. Total change limit was used to measure significant changes within-run variability for both platforms. Results: Most analytes were stable up to day 3 to 4 on both platforms. Serum CO 2 , CL, Ca, ALT and ALB were stable up to 8 days when they were measured on Cobas 8000®. BUN, TRIG, TB, CHOL, AST, ALT and ALB were stable up to 10 days on Dimension® CCS. K showed significant changes at 2h on both platforms at initial measurements. It was out-of-range at day 10 on Dimension® CCS. Serum creatinine levels showed substantial changes at day 2 on Dimension® analyzer and on Cobas 8000® at day 3. Conclusions: The study showed stability of wide range of serum analytes at 20-25°C for several days. The acceptable results can be achieved if samples are centrifuged the same day and analyzed later for most of biochemical analytes.

Background: BarricorTM lithium heparin plasma tubes are new blood tubes that have been introduced to overcome the effects of gel in serum separator tubes (SST) and the shortcomings of standard lithium heparin plasma. We aimed to evaluate BarricorTM tubes as an alternative to serum separator tubes and compare the stability between the tubes. Methods: Forty-four paired samples were collected using both BarricorTM and SST. We compared five analytes at baseline (<6h) and after every 24h using the Passing-Bablok and Bland-Altman plots. Aspartate aminotransferase (AST), potassium (K), phosphate (PO4), lactate dehydrogenase (LDH), and creatinine were analysed in both tubes. We calculated the percentage difference for each analyte between the baseline and time intervals to assess analyte stability. The percentage difference was compared to the desirable specification for bias and reference change value (RCV). Results: All analytes were comparable at baseline. Statistical differences (p<0.001) became evident after 24h. PO4, K, and creatinine had a mean difference that exceeded the desirable specification for bias (-9.59%, -9.35%, and -4.59%, respectively). Potassium was stable up to 24h in both tubes. LDH showed better stability in SST (144h vs. 96h). PO4 concentrations were more stable in both tubes with the SST (96h vs. 72h). Creatinine and AST had the longest stability in both tubes compared to other analytes (144h). Conclusions: Data demonstrated variability and similarities in analyte concentrations and stability, respectively in both tubes