Sara Pasqualetti

Hyperuricemia as risk factor for coronary heart disease incidence and mortality in the general population: a systematic review and meta-analysis

Abstract Previous meta-analyses reported no significant or weak association between hyperuricemia (HU) and coronary heart disease (CHD). We updated the literature search, systematically reviewing retrieved papers. The peer-reviewed literature published from 1965 to December 2014 was searched using Medline and Embase. We included prospective cohort studies involving adults (sample size ≥100) with no cardiovascular disease (CVD) and a follow-up of at least 1 year. Studies were excluded if they considered as outcome the CVD incidence/mortality without separately reporting data on CHD, did not adjusted for major confounders and if the 95% confidence interval (CI) for risk ratio (RR) was not available. Relative risk or hazard ratio estimates, with the corresponding CIs, were obtained. For CHD incidence 12 populations were included (457,915 subjects [53.7% males]). For CHD mortality seven populations were included (237,433 subjects [66.3% males]). The overall combined RR were 1.206 (CI 1.066–1.364, p=0.003) for CHD incidence and 1.209 (CI 1.003–1.457, p=0.047) for CHD mortality, respectively. Subgroup analysis showed a marginal (incidence) and not significant (mortality) association between HU and CHD in men, but an increased risk for CHD incidence and mortality in hyperuricemic women (RR 1.446, CI 1.323–1.581, p<0.0001, and RR 1.830, CI 1.066–3.139, p=0.028, respectively). The risk markedly increases for urate concentrations >7.0 mg/dL. HU appears to increase the risk of CHD events in the general population, mainly in adult women. This finding requires, however, further investigation.

Pre-analytical and analytical aspects affecting clinical reliability of plasma glucose results

The measurement of plasma glucose (PG) plays a central role in recognizing disturbances in carbohydrate metabolism, with established decision limits that are globally accepted. This requires that PG results are reliable and unequivocally valid no matter where they are obtained. To control the pre-analytical variability of PG and prevent in vitro glycolysis, the use of citrate as rapidly effective glycolysis inhibitor has been proposed. However, the commercial availability of several tubes with studies showing different performance has created confusion among users. Moreover, and more importantly, studies have shown that tubes promptly inhibiting glycolysis give PG results that are significantly higher than tubes containing sodium fluoride only, used in the majority of studies generating the current PG cut-points, with a different clinical classification of subjects. From the analytical point of view, to be equivalent among different measuring systems, PG results should be traceable to a recognized higher-order reference via the implementation of an unbroken metrological hierarchy. In doing this, it is important that manufacturers of measuring systems consider the uncertainty accumulated through the different steps of the selected traceability chain. In particular, PG results should fulfil analytical performance specifications defined to fit the intended clinical application. Since PG has tight homeostatic control, its biological variability may be used to define these limits. Alternatively, given the central diagnostic role of the analyte, an outcome model showing the impact of analytical performance of test on clinical classifications of subjects can be used. Using these specifications, performance assessment studies employing commutable control materials with values assigned by reference procedure have shown that the quality of PG measurements is often far from desirable and that problems are exacerbated using point-of-care devices.

The calibrator value assignment protocol of the Abbott enzymatic creatinine assay is inadequate for ensuring suitable quality of serum measurements

The measurement of creatinine in serum is a key indicator of glomerular function of the kidney and its pivotal role in this evaluation has been further increased by recommendations issued by nephrology societies for using equations to estimate the glomerular filtration rate (GFR) [1]. In 2006 the reference system for the measurement of serum creatinine, using suitable higher-order reference materials and reference methods, was completed and internationally promoted [2]. Particularly, the U.S. National Institute for Standard and Technology (NIST) developed the standard referencematerial (SRM) 967 (“Creatinine in frozen human serum”), in which there are two concentration levels with values assigned by isotope dilution-mass spectrometry (IDMS) andwith proven commutability with native serum samples for most of the available commercial creatinine methods [3]. In vitro diagnostic (IVD) manufacturers (re)calibrated their creatinine measurement systems to the internationally agreed reference system to implement the SI traceability of blood creatinine results, with the consequence that for clinical laboratories only standardized assays should remain available. IVD manufacturers may employ different metrological chains and spend substantially different amounts of the total budget of measurement uncertainty just by selecting one or the other of the available traceability chains [4]. This is a central issue as the selection and application of a reference measurement system for calibration of routine methods should be associated with the fulfilment of measurement uncertainty goals based on medical relevance, so that results are suitable for patient management [5]. Using the information on the biological variation of the analyte [www.westgard.com/biodatabase1.htm], to be acceptable, the degree of expanded uncertainty (U) of creatinine measurements for clinical laboratory using unbiased assays on patient samples should stay within approximately ±6.0% or ±9.0% (desirable or minimum quality level, respectively, for imprecision multiplied by a coverage factor of 2), when both the accumulated uncertainty of the corresponding traceability chain and the uncertainty due to the random effects of measurement are included. In our laboratory the serum creatinine measurement is performed with the enzymatic (creatinine hydrolysis to creatine by creatininase) assay (cod. 8L24) on the Abbott Diagnostics Architect c16000 platform. Accordingwith the IVDEUDirective 98/79/EC [6], the analytical system is CEmarked and the calibrator (Multigent Clin ChemCalibrator, cod. 6K30) (CAL) is traceable to theNIST SRM967,with aUof 0.059mg/dL (1.48%) at

Heparinate but not serum tubes are susceptible to hemolysis by pneumatic tube transportation.

Abstract Background: Pneumatic tube transportation (PTT) may induce hemolysis (H) in blood samples. We aimed to compare the H degree before and after PTT implementation in our hospital. Methods: Hemolysis indices (HI) for all lithium-heparin plasma samples (P) drawn by the Emergency Department in 2-month periods were retrospectively collected and pre- (n=3579) and post-PTT (n=3469) results compared. The impact of PTT introduction was investigated on LDH [HI threshold (HIt), 25], conjugated bilirubin (cBIL) (HIt, 30), K (HIt, 100) and ALT (HIt, 125). In addition, HI retrieved for P and paired serum samples collected in silica clot activator tubes (S) from the same venipuncture were compared in pre- (n=501) and post-PTT (n=509) periods. Results: Median (5–95th percentile) HI in P was significantly higher in post-PTT period [7 (0–112) vs. 6 (0–82), p<0.001]. Results reported as ‘Hemolysis’ in P increased from 6.6% in pre-PTT to 9.4% in post-PTT (p<0.001). Investigated tests gave the following rejection rates (pre-PTT vs. post-PTT): LDH, 13.4% vs. 18.8%, p<0.001; cBIL, 9.4% vs. 27.0%, p<0.05; K, 3.7% vs. 5.6%, p<0.001; ALT, 2.9% vs. 4.4%, p<0.01. The slightly higher susceptibility to H of S compared to paired P found in the pre-PTT [9 (1–64) vs. 6 (0–85)] was not confirmed in the post-PTT period [7 (0–90) vs. 8 (1–72)], in which median HI in S was significantly lower (p<0.001) than in pre-PTT. Conclusions: In our setting PTT promotes H in P, increasing the rate of rejected tests. The use of S appears to protect against the hemolysing effect of PTT.

Total laboratory automation: Do stat tests still matter?

During the past decades the healthcare systems have rapidly changed and today hospital care is primarily advocated for critical patients and acute treatments, for which laboratory test results are crucial and need to be always reported in predictably short turnaround time (TAT). Laboratories in the hospital setting can face this challenge by changing their organization from a compartmentalized laboratory department toward a decision making-based laboratory department. This requires the implementation of a core laboratory, that exploits total laboratory automation (TLA) using technological innovation in analytical platforms, track systems and information technology, including middleware, and a number of satellite specialized laboratory sections cooperating with care teams for specific medical conditions. In this laboratory department model, the short TAT for all first-line tests performed by TLA in the core laboratory represents the key paradigm, where no more stat testing is required because all samples are handled in real-time and (auto)validated results dispatched in a time that fulfills clinical needs. To optimally reach this goal, laboratories should be actively involved in managing all the steps covering the total examination process, speeding up also extra-laboratory phases, such sample delivery. Furthermore, to warrant effectiveness and not only efficiency, all the processes, e.g. specimen integrity check, should be managed by middleware through a predefined set of rules defined in light of the clinical governance.

Cystatin C provides a better estimate of the effect of glomerular filtration rate on serum human epididymis protein 4 concentrations.

Abstract Background: We evaluated the effect of kidney glomerular function on serum concentrations of human epididymis protein 4 (HE4) using creatinine (Cr), cystatin C (CysC) and related chronic kidney disease epidemiology collaboration (CKD-EPI) equations. Methods: We enrolled 101 women aged ≤56 years with a glomerular filtration rate (GFR) (estimated by CKD-EPI eGFRCr) ranging from 60 to 120 mL/min/1.73 m2, free of any disease and biological and life-style factors known to influence serum HE4 concentrations, and we measured serum Cr, CysC and HE4 concentrations. Cr and CysC values were included in the three CKD-EPI equations to obtain GFR estimates. Results: A statistically significant increase in HE4 median concentrations was detected in subjects with an eGFRCr between 60 and 74 mL/min/1.73 m2 when compared with those with an eGFR >90 mL/min/1.73 m2 (54.2 vs. 42.2 pmol/L, p=0.003). Regression models showed that CysC measurement per se and eGFRCysC were the most sensitive markers to catch HE4 increases due to a mild decrease in renal function [adjusted r2, 0.38 (p=0.00003) and 0.37 (p=0.0004), respectively]. By assuming baseline CysC and eGFRCysC at 0.80 mg/L and 101.5 mL/min/1.73 m2, an increase of 0.10 mg/L in CysC concentrations and a decrease of 10 mL/min of eGFRCysC implied an average (±SE) increase in serum HE4 concentrations of 9.2 (±1.2) and 8.8 (±1.1) pmol/L, respectively. Conclusions: Our study shows that a better estimate of the effect of GFR on serum HE4 is obtained by measuring CysC in serum or using CKD-EPI eGFRCysC equation.

Optimal collection tubes for plasma glucose determination: confusion reigns supreme.

*Corresponding author: Sara Pasqualetti, UOC Patologia Clinica, Ospedale “Luigi Sacco”, ASST Fatebenefratelli-Sacco, Via GB Grassi 74, 20157 Milano, Italy, Phone: +390239042683, Fax: +390239042364, E-mail: sara.pasqualetti@asst-fbf-sacco.it Dominika Szőke, Sarah Birindelli, Alberto Dolci and Mauro Panteghini: UOC Patologia Clinica, Ospedale “Luigi Sacco”, ASST Fatebenefratelli-Sacco, Milan, Italy Letter to the Editor

Clinical impact of glycolysis inhibition on plasma glucose results requires caution

Clinical laboratories should strive to produce accurate results as much as possible. In the case of plasma glucose (PG) measurement, sources of preanalytical bias have been identified. In their recent letter, Carta et al. compared the performance of several specimen tubes that use blood acidification. Except for Venosafe tubes (Terumo Europe N.V., Leuven, Belgium), alternatives using citrate gave results that were significantly biased when compared to the reference. (The Venosafe tubes have been withdrawn from the market.) The reported results corroborate our previous data. We concluded that caution needs to be exercised in applying recommendations regarding the use of citrate in the light of the available experimental evidence on the performance of different tubes. We wish to highlight another point regarding the potential impact of the use of citrate on patient classification. In our experience, the percentage of outpatients with fasting PG 55.6mmol/L increased from approximately 25 to 45%, when Venosafe tubes replaced classical fluoride/oxalate tubes. Although expert groups recommended as urgent the introduction of citrate tubes, we still await the official position of professional groups representing clinical diabetes specialists regarding the decision limits that should be applied to fasting PG – should these be redefined when tubes are used that promptly inhibit in vitro glycolysis – or should they be maintained, so that more subjects at increased risk for diabetes will be identified earlier? This is not the only example where adoption of a novel approach to specimen collection in laboratory medicine has affected the results obtained, raising issues for decision limits. The effect of analytical and preanalytical changes on patient results requires that decision limits be reviewed, if patient expectations and even outcomes are not to be adversely affected. Current fasting PG cut-off points are derived from studies using sodium fluoride tubes. Thus, the decision limits used by physicians are based on data that were generated with approaches in collecting blood that were negatively biased. This applies to other clinical settings as well as diabetes diagnosis and management. For example, paediatricians measure PG during insulin tolerance test in children with suspected growth hormone deficiency. Decision limits for hypoglycaemia are likewise based on studies using sodium fluoride tubes. Revised blood collection procedures involving the use of citrate challenge these clinical criteria, putting into the normoglycaemic range subjects previously categorized as hypoglycaemic. Thus, it is essential that the clinical decision limits should be adjusted to ensure that patient care remains consistent despite the changes. Alternatively, clinicians must advise patients on the clinical improvement deriving from the change.

Are blood ammonia concentrations dependent on γ-glutamyl-transferase levels in plasma?

To the Editor, We read with interest the letter by Schuff-Werner and Steiner1 that commented a recently published article dealing with the evaluation of the short- and long-term storage stability of plasma ammonia.2 We were particularly impressed by the authors’ claim that blood ammonia values may significantly depend on the activity of γ-glutamyl-transferase (GGT) in plasma. They support this conclusion by reporting experimental results obtained in two samples with low and increased GGT catalytic concentrations stored up to 6 h either at room temperature or at 4°C.1 Several, mostly preanalytical, factors, like haemolysis and poor specimen quality, skin contamination and delayed analysis in general, may cause artificial increase of blood ammonia.3 ,4 If the systematic detection of haemolysis through the automatic photometric measurement of haemolysis index (HI) is now relatively common, it is more difficult for laboratories to keep the time short between blood drawing and analysis. To prevent an artificial increase of ammoniaemia caused by the metabolism of red blood cells due …

More on the accuracy of the Architect enzymatic assay for hemoglobin A1c and its traceability to the IFCC reference system.

*Corresponding author: Dominika Szőke, UOC Patologia Clinica, Azienda Ospedaliera “Luigi Sacco”, Via GB Grassi 74, 20157 Milan, Italy, Phone: +39 02 39042683, Fax: +39 02 39042364, E-mail: szoke.dominika@hsacco.it; and Clinical Pathology Unit, “Luigi Sacco” University Hospital, Milan, Italy Assunta Carnevale and Sara Pasqualetti: Clinical Pathology Unit, “Luigi Sacco” University Hospital, Milan, Italy Federica Braga and Renata Paleari: Centre for Metrological Traceability in Laboratory Medicine (CIRME), University of Milan, Milan, Italy Mauro Panteghini: Clinical Pathology Unit, “Luigi Sacco” University Hospital, Milan, Italy; and Centre for Metrological Traceability in Laboratory Medicine (CIRME), University of Milan, Milan, Italy Letter to the Editor