Determination of cotinine by LC-MS-MS with automated solid-phase extraction.

Cotinine is the primary metabolite of nicotine and the preferred biomarker for assessing cigarette smoke exposure. Several liquid chromatography-tandem mass spectrometry (LC-MS-MS) methods have been described for measuring cotinine in biological fluids. Sample preparation typically involves manual solvent evaporation and reconstitution steps. This study describes a novel LC-MS-MS method for the quantification of cotinine by using electrospray ionization with multiple reaction monitoring and cotinine-d3 as internal standard, coupled with an automated solid-phase extraction (SPE) procedure. The assay was linear over the analytical range of 0.5-1,000 ng/mL. The limits of detection and quantification were 0.13 and 0.20 ng/mL, respectively. Intra-assay and inter-assay imprecision of cotinine in all samples was <5 and <10% (coefficient of variation), respectively. The analytical recovery of cotinine spiked into plasma was >95-100%. Matrix effects in serum and plasma were <10%. A rapid, sensitive and specific LC-MS-MS method was developed and validated for the determination of cotinine in human plasma, using a straightforward automated SPE protocol. The application of this method to an epidemiological study has demonstrated its utility for batch analyses of a large sample set (>500 samples).

The impact of centrifugation in primary care on pseudohyperkalaemia: a retrospective evaluation.

BACKGROUND: Spurious hyperkalaemia is a relatively common occurrence in samples originating from primary care. Failure to identify spurious hyperkalaemia carries a significant risk of patient mismanagement. We have carried out a retrospective evaluation to review the impact of the use of centrifuges in primary care for biochemistry blood samples on the management of hyperkalaemia. METHODS: Serum potassium concentrations in samples received from primary care were reviewed for six months prior to and after the implementation of on-site centrifugation. Samples exhibiting significant hyperkalaemia (serum potassium >6.0 mmol/L) were further investigated to ascertain the degree of patient follow-up. RESULTS: There was a significant decrease in the number of samples exhibiting marked hyperkalaemia following the implementation (2244 versus 524; P < 0.0001). In terms of patient follow-up, we observed a reduction in the number of patients exhibiting pseudohyperkalaemia that previously had led to inappropriate hospital admissions over the same time period (6 cases postimplementation versus 22 cases preimplementation). We also observed an increase in the number of patients exhibiting true hyperkalaemia during the six-month period postimplementation (33 cases postimplementation versus 6 cases preimplementation). CONCLUSIONS: The centrifugation of serum samples in primary care improves the sample quality and the integrity of the potassium results reported. We have also demonstrated evidence of an improvement in patient management and quality of care.

Seasonal pseudohyperkalaemia: no longer an issue?

BACKGROUND: Spurious hyperkalaemia is a well-recognized problem when reporting potassium results in samples originating from Primary Care. This is particularly relevant in laboratories serving large geographical areas where sample transport can cause significant delays in sample centrifugation. We have carried out a retrospective audit comparing serum potassium results on samples centrifuged at the general practice (GP) with those centrifuged on arrival at the clinical laboratory. METHODS: Potassium results were reviewed on serum samples received from 87 GPs in the Grampian region between August 2010 and March 2011. Potassium results were compared between samples centrifuged at the practice versus those centrifuged on arrival at the clinical laboratory. RESULTS: In the period between November 2010 and February 2011, median monthly serum potassium results were significantly different between samples centrifuged at practices and those centrifuged on arrival at the laboratory. Median potassium concentrations were 10.2% higher in January 2011 (4.8 mmol/L; interquartile range [IQR]: 4.5-5.1) compared with August 2010 (4.3 mmol/L; IQR: 4.0-4.6). A similar trend in monthly median potassium concentrations was not evident in samples centrifuged at source over the same period. CONCLUSIONS: The introduction of centrifuges into all GPs across NHS Grampian has significantly reduced the effect of seasonal variation in serum potassium results. There has also been a concurrent reduction in the number of cases of spurious hyperkalaemia. This exercise has significantly improved the overall quality of potassium results reported to Primary Care.