on Venous and Capillary Blood Samples

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1 Evaluation of the Sebia CAPILLARYS Flex Piercing for the Measurement of on Venous and Capillary Blood Samples Olivier Heylen, MSc, Stefaan Van Neyghem, MLT, Sandra Exterbille, MLT, Charline Wehlou, MD, Frans Gorus, MD, PhD, and Ilse Weets, MD, PhD From the Department of Clinical Chemistry and Radio-immunology, Universitair Ziekenhuis Brussel, Brussels, Belgium. Key Words: Analytical performance; Capillary zone electrophoresis; Hemoglobin A c ; HPLC Am J Clin Pathol June ;:8-8 DOI:.9/AJCPRUQCJBANSV ABSTRACT Objectives: We evaluated the Sebia CAPILLARYS Flex Piercing (Cap FP; Sebia, Lisses, France) for measurement of hemoglobin A c ( ) on venous and capillary blood samples. Methods: We analyzed whole-blood samples and control materials with the Cap FP and Tosoh G8 (Tosoh Corporation, Tokyo, Japan). Capillary blood samples were analyzed on the Cap FP on different storage conditions and were compared with venous samples. Results: Both instruments achieved total imprecision of less than.% (International Federation of Clinical Chemistry units). Bias was mmol/mol or less and mmol/mol or less for the Cap FP and Tosoh G8, respectively. The Cap FP was not prone to common interferences. The Tosoh G8 showed significant bias only for carbamylated hemoglobin and did not completely separate hemoglobin D and hemoglobin E. On the Cap FP, storage of capillary blood at room temperature showed no significant bias. There was good agreement with venous blood. Conclusions: The Cap FP and Tosoh G8 perform excellently for determination. Capillary blood can be analyzed on the Cap FP as an acceptable alternative to venous blood and point-of-care testing. Home collection and central analysis of capillary blood could contribute to a reduction of health care costs without reducing quality of determination. Hemoglobin A c ( ) measurement is widely accepted as the most important marker for glycemic control and assessment of the risk of chronic complications both in type and type diabetes mellitus. - Since the American Diabetes Association has introduced as one of the parameters that can be used for the diagnosis of diabetes, has gained importance as a biological marker. In view of the diabetes epidemic worldwide, the number of determinations will increase. Over the past years, major efforts have been made to standardize the determination. In a first phase, values were aligned with the Diabetes Control and Complications Trial Research Group (DCCT), and currently, it is recommended that methods are standardized according to the International Federation of Clinical Chemistry (IFCC) reference method. In parallel with the evolution toward standardization of the determination, criteria for precision and accuracy as well as for diabetes control became more stringent. The methods most commonly used to quantify are immunoassays, ion-exchange high-performance liquid chromatography (HPLC), boronate affinity HPLC, and enzymatic assays. More recently, capillary zone electrophoresis (CZE) has been introduced for the determination. Both the HPLC and CZE methods have the advantage of showing the presence of hemoglobin variants, which is mainly of importance for the interpretation of results if there is a high frequency of hemoglobin variants in the background population.,8 Potential devices for home samples comprise capillary sampling and dried blood spot on filter paper. Samples can be taken at home, are easy to send by regular mail, and can be Downloaded from Am J Clin Pathol ;: DOI:.9/AJCPRUQCJBANSV 8

2 Heylen et al / Evaluation of CAPILLARYS Flex Piercing analyzed before going to the physician for treatment evaluation. 9 Besides saving extra travel for the patient to the clinician for a phlebotomy, intensive follow-up by home sampling improves glycemic control and therefore is especially interesting for patients with poor metabolic control (eg, children, adolescents, and the elderly). Recent studies have been published regarding the performance of the recently commercially released Sebia CAPIL- LARYS Flex Piercing analyzer (Sebia Cap FP; Sebia, Lisses, France).,, In this evaluation, we studied the Sebia Sebia Cap FP and the Tosoh G8 for the determination of in comparison with the Tosoh G instrument (Tosoh Corporation, Tokyo, Japan). In addition, we focused on the determination of on the Sebia Cap FP in a conventional and capillary blood sample in terms of bias between both sample types and stability in different conditions for the capillary sample. glycidyl methacrylate-ethylene glycol methacrylate copolymer cation-exchange column (TSKgel Glyco His, Tokyo, Japan) maintained at C in an aluminum block oven. Each hemoglobin fraction is eluted from the column by a step gradient of three buffers with increasing ionic strength. Approximately µl of whole blood is automatically diluted (/) with hemolysis and wash dilution in the dilution port. Next, the diluted sample is injected onto the column, and the separated fractions are continuously monitored by the diode detector system at and nm. Comparison Instrument The HLC-G (Tosoh G; Tosoh Corporation) analyzer, which is routinely used in our laboratory, was used as a comparator. The Tosoh G instrument was used according to the manufacturer s instructions with the Tosoh calibration materials. Specimens Materials and Methods Analyzers Sebia Cap FP The Sebia Cap FP instrument is an automated analyzer for the quantitative analysis of proteins (serum and urine), immunotyping (serum and urine), hemoglobin variants, carbohydrate-deficient transferrin, and, more recently,. The CAPILLARYS kit is based on the CZE principle, where hemoglobin fractions are separated by their charge in an alkaline buffer (ph 9.). By using this buffer, hemoglobins are detected in the following order, from cathode to anode: A /C, E, S, D, F, A, other hemoglobin A (HbA), and finally A c. The Sebia Cap FP analyzer has eight silica capillaries functioning in parallel, thus allowing eight simultaneous analyses for. Before each run, the capillaries are washed with wash solution and prepared for the next analysis with buffer. Then, 8 µl of the whole-blood sample is automatically diluted (/) with a hemolyzing solution and is injected at the anodic end of the capillary by hydrodynamic injection. A high-voltage protein separation is then performed and direct detection of the hemoglobins is made at the cathodic end of the capillary at nm. Tosoh G8 Analyzer The Tosoh HLC-G8 (Tosoh G8; Tosoh Corporation) instrument is a fully automatic HPLC benchtop analyzer for the determination of and hemoglobin variants. The Tosoh G8 separates the various components of hemoglobin into six fractions. Separation is achieved by a nonporous Control Samples Quality control materials used throughout the evaluation were Lyphochek Diabetes Control Levels and (Bio-Rad Laboratories, Irvine, CA) and CAPILLARYS Control and (Sebia). Both are human lyophilized whole-blood assayed controls. External quality control (EQC) samples supplied by the Wetenschappelijk Instituut Volksgezondheid Institut Scientifique de Santé Publique (WIV-ISP; Belgian Scientific Institute for Public Health, Brussels, Belgium) were used for bias evaluation. The samples contain lyophilized hemolysate of human origin, and the targets were set by an IFCC reference method. Patient Samples Venous blood samples were collected into S-Monovette potassium EDTA tubes (Sarstedt, Nürnbrecht, Germany). Capillary blood samples were collected by finger prick into -μl EDTA End-to-End capillaries (Sarstedt), which were subsequently stored into screw-cap microtubes (Sarstedt) either with or without hemolysis reagent (Sebia). This study was a prospective study of samples submitted for routine analysis of. Residual material of whole-blood samples from diabetic and nondiabetic patients attending the UZ Brussel (Brussels, Belgium) was included. The samples in this study were used according to procedures supervised by local authorities responsible for ethical research. All results were expressed in IFCC units. The relationship between the IFCC units and DCCT/National Glycohemoglobin Standardization Program (NGSP) results is defined by the following master equation: NGSP = (.9 IFCC) Am J Clin Pathol ;:8-8 Downloaded 88 from DOI:.9/AJCPRUQCJBANSV

3 Evaluation Protocol Bias Estimation Trueness was tested according to Clinical and Laboratory Standards Institute (CLSI) EP9-A guidelines using EQC samples of the national health care survey supplied by the WIV-ISP (; n = ). Linear regression analysis was performed and bias was estimated at levels of,, and 9 mmol/mol. Imprecision Within-run imprecision was determined by replicates at two concentrations, using blood from a diabetic and a nondiabetic participant. Total imprecision was estimated according to CLSI EP-A guidelines. This was done with single lots of reagents and columns by processing two runs per day during days, using the bilevel Lyphochek controls. Performance data were first evaluated by the Grubbs outlier test, followed by calculation of the mean, standard deviation, and coefficient of variation (CV). Method Comparison Each test instrument was individually compared with the same comparative in-house instrument. Samples over a broad range from diabetic and nondiabetic participants attending the hospital were analyzed over at least operating days. Assessment of between-method outliers was performed by visual inspection of the plots and by statistical outlier testing according to CLSI EP9-A guidelines. Data were analyzed by Passing-Bablok regression analysis and by absolute difference plot. Linearity Linearity was assessed following the CLSI EP-A guidelines by mixing a high and a low sample. The wholeblood samples were hemolyzed first and then proportionally mixed. Linear regression analysis of expected vs observed values obtained in duplicates was then performed, after visual inspection for outliers. Carryover Carryover between blood samples with a low (L) and a high (H) concentration was checked by analyzing them in the following order: L, H, L, H, L, H, L, H, L, H, and L. Results were calculated according to EP-Evaluator Release 9 (David G Rhoads Associates, Kennett Square, PA). Assessment of Interfering Substances As described in CLSI EP-A guidelines, the potential error caused by potentially interfering substances (labile, carbamylated hemoglobin, bilirubin, triglycerides, and hemoglobin content) was compared with an allowable error that was set prior to conducting the interference experiments. According to the criteria of the national health care survey of the WIV-ISP, the allowable error was set at mmol/mol. The influence of hemoglobin variants was also investigated. Labile A c Influence of labile A c was examined by incubating erythrocytes of three patients (one with normal and two with elevated values) with glucose solutions up to 8 mmol/l to increase the labile fraction. Erythrocytes were incubated at C for hours with mixing every minutes. Carbamylated Hemoglobin Erythrocytes from three different patients (one with normal and two with elevated values) were incubated with various concentrations of potassium cyanate (up to mmol/l) for hours at C to achieve in vitro carbamylation of the hemoglobin. Lipemia and Bilirubin Interference of triglycerides and bilirubin was assessed by mixing erythrocytes of two patients (one with normal and one with elevated values) with lipemic plasma and with icteric plasma to achieve final concentrations of mmol/l triglycerides and 8 µmol/l bilirubin, respectively. Hemoglobin Content The effect of the hemoglobin concentration on the value was evaluated by manually diluting one whole-blood sample with a normal value with saline, thus obtaining hemoglobin values ranging from to. g/l. Hemoglobin Variants The capacity of demonstrating the presence of hemoglobin variants and correctly reporting the percentage was investigated using samples containing hemoglobin AS, hemoglobin AC, hemoglobin AD (HbAD), and hemoglobin AE (HbAE). Capillary on Sebia Cap FP Stability of on capillaries during storage and transport in different weather conditions was evaluated by preparing capillary samples from venous blood samples (one normal and two elevated values) and storing them at C to 8 C, room temperature (RT), and C for up to 8 days, with and without Sebia hemolyzing solution. Agreement of venous blood samples and simultaneously obtained capillary blood from the fingertip of healthy volunteers and 8 diabetic patients was also evaluated. Capillary blood samples were analyzed after days of storage at RT in Sebia hemolyzing Downloaded from Am J Clin Pathol ;: DOI:.9/AJCPRUQCJBANSV 89

4 Heylen et al / Evaluation of CAPILLARYS Flex Piercing solution. The allowable bias was set at mmol/mol, according to the criteria of the national health care survey of the WIV-ISP. 8 Statistical Analysis Statistical and graphical analysis was performed with Analyse-it software, version. (Analyse-it Software, Leeds, England) and Microsoft Excel (Microsoft, Redmond, WA). Results Bias Estimation Bias values are shown in Table. Linear regression analysis showed a slope of. and an intercept of.8 for the Tosoh G8 and a slope of. and an intercept of.8 for the Sebia Cap FP. Bias at levels of,, and 9 mmol/mol are shown in Table. The bias increases at higher levels for the Tosoh G8 but still remains acceptable, while Sebia Cap FP shows overall excellent trueness according to the analytical goals from the national health care survey of the WIV-ISP. 8 Imprecision Results for within-run and total imprecision are shown in Table. CVs below.% for both analyzers show excellent precision based on the analytical goals from the national health care survey of the WIV-ISP. 8 Method Comparison Passing-Bablok regression analysis of the data from the comparison between the Sebia analyzer and the Tosoh G Figure A showed a slope (9% confidence interval [CI]) of.9 (.9-.9) and an intercept of. (.8-.). Absolute difference plot Figure B showed a mean difference of. mmol/mol. Passing-Bablok regression analysis for the Tosoh G8 vs Tosoh G Figure C yielded a slope (9% CI) of.98 (.9 to.99) and an intercept of. (.89 to.). Data from the absolute difference plot Figure D showed a mean difference of. mmol/mol when comparing the Tosoh G8 with the Tosoh G. Linearity Linear regression analysis of the data obtained by proportional mixing of hemolysates containing low and high concentration is shown in Table. Linearity was demonstrated between 9 and mmol/mol for both analyzers, with the 9% CI for the intercept and slope comprising and, respectively. Carryover With a carryover of. and. for the Sebia Cap FP and Tosoh G8, respectively, results were below the error Table Overall Performance Characteristics for the Measurement of on the Tosoh G8 and Sebia Cap FP Parameter Tosoh G8 Sebia Cap FP Trueness (EP9), mmol/mol Bias at mmol/mol Bias at mmol/mol Bias at 9 mmol/mol Imprecision (EP) Within-run imprecision, % CV at mmol/mol..8 CV at mmol/mol.. Total imprecision, % CV at mmol/mol.. CV at 8 mmol/mol..8 Linearity (EP) Intercept (9% CI). (. to.). (. to.8) Slope (9% CI). (.98 to.).99 (.9 to.) Carryover Not significant Not significant Interferences (EP) Labile A c (8 mmol/l glucose) Bias < mmol/mol Bias < mmol/mol Carbamylated hemoglobin ( mmol/l KCNO) Bias up to mmol/mol Bias < mmol/mol Bilirubin (8 µmol/l) Bias < mmol/mol Bias < mmol/mol Lipemia (triglycerides mmol/l) Bias < mmol/mol Bias < mmol/mol Hemoglobin content (hemoglobin - g/l) Bias < mmol/mol Bias < mmol/mol Hemoglobin AS HbS separated from other fractions HbS separated from other fractions Hemoglobin AC HbC separated from other fractions HbC separated from other fractions Hemoglobin AD HbD elutes just after HbA HbD separated from other fractions Hemoglobin AE HbE coelutes with HbA HbE separated from other fractions CI, confidence interval; CV, coefficient of variation; HbA, hemoglobin A; HbC, hemoglobin C; HbD, hemoglobin D; HbE, hemoglobin E; HbS, hemoglobin S; KCNO, potassium cyanate. 8 Am J Clin Pathol ;:8-8 Downloaded 8 from DOI:.9/AJCPRUQCJBANSV

5 limit (. for the Sebia Cap FP and. for the Tosoh G8), which indicates the absence of carryover between high and low samples. Assessment of Interferences Assessment of interferences is summarized in Table. Labile A c On the Tosoh G8, peaks identified as labile A c increased as a function of glucose concentration. All samples showed no significant bias at glucose concentrations up to 8 mmol/l. On the Sebia analyzer, values were within ± mmol/ mol of the baseline values for all three patient samples, which is significantly below the total allowable error. Carbamylated Hemoglobin On the Tosoh G8, the in vitro experiments with potassium cyanate showed that the labile fraction increased for all three investigated samples, while the observed bias for the normal and one elevated sample did not exceed the total allowable bias with potassium cyanate concentrations up to mmol/l. However, for the highest sample with a baseline value of mmol/mol, a negative bias of mmol/mol was observed at a potassium cyanate concentration A B Sebia Cap FP ( mmol/mol) Difference (Sebia Cap FP Tosoh G) Tosoh G ( mmol/mol) Mean C D Tosoh G8 ( mmol/mol) Difference (Tosoh G8 Tosoh G) Tosoh G ( mmol/mol) Mean Figure Passing-Bablok regression analysis and absolute difference plot of hemoglobin A c ( ) results, using whole-blood patient samples, obtained with the Sebia Cap FP (Sebia, Lisses, France) (A, B) and the Tosoh G8 (Tosoh Corporation, Tokyo, Japan) (C, D) compared with the Tosoh G (Tosoh Corporation). Passing-Bablok: blue solid line (with 9% confidence interval [CI]) represents the linear curve. Absolute difference plot: blue solid line (with 9% CI) represents mean absolute difference, while light blue dashed lines (with 9% CI) represent 9% limits of agreement. Downloaded from Am J Clin Pathol ;: DOI:.9/AJCPRUQCJBANSV 8

6 Heylen et al / Evaluation of CAPILLARYS Flex Piercing of mmol/l. On Sebia Cap FP, the other HbA fractions increased with increasing potassium cyanate concentrations. However, all values were within ± mmol/mol of the baseline values of all three patient samples. Lipemia and Bilirubin Since measured values were within ± mmol/mol of the baseline values for both analyzers, no interference was observed on a sample with a normal and an elevated value with up to mmol/l triglycerides and 8 µmol/l bilirubin. Hemoglobin Content Dilutions of a patient sample with 9 mmol/mol, generating hemoglobin concentrations from g/l (undiluted) down to. g/l, were assessed for separation profiles, total chromatographic area, and results on the Tosoh G8. This range of dilutions resulted in areas of,9 to units, and all provided good resolution and satisfactory integration without significant bias. The same evaluation was done for the Sebia Cap FP by judging results and total optical density values. At a theoretical hemoglobin concentration of. g/l, there is a significant A Percent AA.8%. min AB.%. min.. F.%.9 min SAC 8.%/ mmol LAC+.%.9 min....8 A 8.%.9 min P.%. min P.%.9 min H-V 8.9%.8 min P.9%.9 min HbS B Percent AA.%. min AB.8%. min.. F.%.8 min SAC.8%/ mmol LAC+.%.9 min....8 A 8.%.9 min P.% min P.8%.8 min H-V.%. min HbC Figure Hemoglobin A c ( ) chromatograms on the Tosoh G8 (Tosoh Corporation, Tokyo, Japan) for some variant hemoglobins (labeled peaks), showing resolution of the separation. Hemoglobin S (HbS) (A), hemoglobin C (HbC) (B). 8 Am J Clin Pathol ;:8-8 Downloaded 8 from DOI:.9/AJCPRUQCJBANSV

7 negative bias of mmol/mol, but adequate resolution and integration without significant bias was obtained for concentrations greater than g/l. Hemoglobin Variants The chromatograms of the Tosoh G8 for the most common hemoglobin variants in our population are shown in Figure. These illustrate that the investigated variant hemoglobins were separated from other fractions, except for hemoglobin D, which elutes just after HbA, and hemoglobin E, which elutes together with the HbA fraction and thus generates a falsely decreased value. On the Sebia Cap FP, all the variants investigated were clearly separated and was quantified reliably Figure. Capillary on the Sebia Cap FP Stability of the result on capillaries with different storage conditions is shown in Figure. 8 The normal and two elevated samples did not exceed ± mmol/ mol after 8 days of storage at C to 8 C and RT. At a normal value of mmol/mol, the bias remained within the allowable range after 8 days of storage at C. C Percent AB.9%. min FP.%. min AA.9%. min.. SAC.9%/ mmol F.8%. min LAC+.%. min....8 A 88.%.9 min H-V.%.98 min HbD P.%. min P.%. min D Percent AA.%. min FP.%. min AB.99%. min.. F.%.9 min SAC.9%/ mmol LAC+.8%.9 min....8 A 9.8%.9 min HbA + HbE Figure (cont) Hemoglobin D (HbD) C), and unresolved hemoglobin E (HbE) coeluting with hemoglobin A (A). D). The red-shaded peak is. AA, hemoglobin A a ; AB, hemoglobin A b ; F, hemoglobin F; LAC, labile. Downloaded from Am J Clin Pathol ;: DOI:.9/AJCPRUQCJBANSV 8

8 Heylen et al / Evaluation of CAPILLARYS Flex Piercing In the sample with an elevated level of mmol/ mol stored at C, however, the positive bias exceeded mmol/mol after days and increased to mmol/mol after 8 days. The sample with the highest concentration (88 mmol/mol) stored at C showed a positive bias of mmol/mol after days, which increased further to mmol/ mol after 8 days. Storage with or without Sebia hemolyzing solution yielded similar results. However, in the latter A B HbA HbA HbC HbS HbF or variant HbA HbA Other c Hb Other Hb Electrophoresis Electrophoresis Fractions % Ref % mmol/mol Ref mmol/mol Fractions % Ref % mmol/mol Ref mmol/mol Other Hb Hb A HbF or variant HbA Other Hb HbA C HbA D HbA HbD HbE HbA Other Hb HbA Other Hb Electrophoresis Electrophoresis Fractions Other Hb HbA HbA % Ref %. mmol/mol Ref mmol/mol. Fractions Other Hb HbA HbA Figure Hemoglobin A c ( ) electropherograms on the Sebia Cap FP (Sebia, Lisses, France) for some variant hemoglobins (labeled peaks), showing the resolution of the separation. Hemoglobin S (HbS) (A), hemoglobin C (HbC) (B), hemoglobin D (HbD) (C), and hemoglobin E (HbE) (D). % Ref %. mmol/mol Ref mmol/mol. 8 Am J Clin Pathol ;:8-8 Downloaded 8 from DOI:.9/AJCPRUQCJBANSV

9 condition, results could no longer be obtained for all three samples after 8 days of storage at C. In these samples, calculation was not possible because of pronounced degradation of the profile with distortion of and/or HbA peaks. Passing-Bablok regression analysis comparing the capillary samples without hemolyzing solution and the venous samples Figure A showed a borderline significant slope and intercept of. (9% CI,. to.) and.8 (9% CI,. to.), respectively. 8 Passing-Bablok regression analysis comparing the capillary samples with hemolyzing solution and the venous samples showed similar results Figure C. The slope and intercept were. (9% CI,. to.) and.9 (9% CI,. to.), respectively. Absolute difference plots Figure B and Figure D showed a good agreement between the venous and capillary finger prick samples. After storage days at RT, none of the analyzed capillary samples stored with the Sebia hemolyzing solution showed a bias greater than mmol/mol while one stored without Sebia hemolyzing solution showed a negative bias greater than mmol/mol as compared with the venous sample. The mean bias observed for capillary samples against venous samples was mmol/mol in both conditions (with or without Sebia hemolyzing solution). Discussion For diagnosis and monitoring of diabetes mellitus, it is crucial to measure with an analyzer that provides precise and accurate results. 9, Reproducibility studies showed that CVs met the stringent requirements of the national health care survey. One should keep in mind that imprecision is expressed in IFCC units and thus should not be compared with imprecision results of other analyzers expressed in DCCT units, since CVs are smaller when using the latter. Estimation of trueness was excellent for the Sebia Cap FP. For the Tosoh G8, the bias tended to increase at higher concentrations but was still acceptable. Linearity was demonstrated over a broad clinical range of values, and no carryover was found for both analyzers. In our experiments, we have shown that the Sebia Cap FP was not subjected to the most common interferences. The Tosoh G8 yielded equally good results for most interferants with a few exceptions. First, there was a significant negative bias at the highest concentration of potassium cyanate, due to the appearance of carbamylated hemoglobin in the peak of labile A c. Since this elevated fraction was not seen in samples of patients undergoing uremic dialysis (data not shown), our experiment was probably conducted with concentrations of potassium cyanate that generate carbamylated hemoglobin A B 8 Days of Storage 8 Days of Storage C 9 8 Figure Stability of capillary hemoglobin A c ( ) during storage with (solid lines) and without (dashed lines) hemolyzing solution on a low (A), elevated (B), and highly elevated (C) sample on the Sebia Cap FP (Sebia, Lisses, France). Blue lines represent storage at C to 8 C, purple lines show storage at room temperature, and green lines show storage at C. Orange dashed lines represent the total allowable error, set at ± mmol/mol. 8 8 Days of Storage Downloaded from Am J Clin Pathol ;: DOI:.9/AJCPRUQCJBANSV 8

10 Heylen et al / Evaluation of CAPILLARYS Flex Piercing concentrations that are not even seen in individuals with endstage renal disease. Nevertheless, we suggest paying attention to samples showing an increase in the labile A c fraction for the Tosoh G8. Second, falsely decreased values could be obtained because HbAD is not fully separated from HbA and because of coelution with HbA of HbAE and glycated hemoglobin S., Diabetologists stress the importance of having an result at the time of the patient s visit to the doctor to improve patient management. This can be performed through point-ofcare testing (POCT) or through home sampling. Analytical performance of POCT instruments has been largely disappointing so far., Moreover, shipment of capillary blood to the central laboratory has the advantage over POCT in that it is measured by the same measurement method as for the venous samples. 9 Storage of capillary samples during several days showed an increasing positive bias at higher temperatures. Although this situation could possibly occur during summertime, it is rather unlikely that these high temperatures arise continuously during the entire mailing process. Furthermore, it is shown that capillary results did not significantly differ from each other when mailed during winter or summer. Our study demonstrates that capillary blood samples can reside at room temperature for at least days before being assayed. In support of the use of capillary blood, there was good agreement A B H Capillary 8 Difference ( H Capillary Venous ) 8 Venous 8 Venous C D +H Capillary 8 Difference (+H Capillary Venous ) 8 8 Venous Venous Figure Passing-Bablok regression analysis and absolute difference plot of capillary hemoglobin A c ( ) without (A, B) and with (C, D) hemolyzing solution compared with venous on the Sebia Cap FP (Sebia, Lisses, France). Green dots represent nondiabetic patient samples, while red dots are the diabetic patient samples. Passing-Bablok: blue solid line (with 9% confidence interval [CI]) represents the linear regression curve. Absolute difference plot: blue solid line (with 9% CI) represents mean absolute difference, while orange dashed lines represent the total allowable error, set at ± mmol/mol. 8 8 Am J Clin Pathol ;:8-8 Downloaded 8 from DOI:.9/AJCPRUQCJBANSV

11 between the venous and capillary samples. In fact, only one of 8 samples exceeded the allowable bias. The collection of this capillary blood sample from a healthy volunteer went more difficult than usual, and the sample was stored without hemolyzing solution. We conclude that capillary samples taken at home for measurement on the Sebia Cap FP are an acceptable, easy, and inexpensive alternative for venous blood samples when preanalytical factors such as mailing time and temperature are well controlled. This can provide the clinician with timely and important information at the moment of the patient s consultation without the need for an extra visit for a phlebotomy and with state-of-the-art allowable error. This strategy should be particularly beneficial for diabetic children and the elderly. Address reprint requests to Dr Weets: Dept of Clinical Chemistry, Universitair Ziekenhuis Brussel, Laarbeeklaan, Brussels, Belgium; ilse.weets@uzbrussel.be. Tosoh Bioscience Belgium and Sebia Benelux provided the Tosoh G8 and CAPILLARYS Flex Piercing analyzers and reagents used in this evaluation. The evaluation of capillary sampling was part of a Sebia R&D development project. References. UK Prospective Diabetes Study (UKPDS) Group. Effect of intensive blood-glucose control with metformin on complications in overweight patients with type diabetes (UKPDS ). Lancet. 998;:8-8.. Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med. 99;: Gorus F, Mathieu C, Gerlo E. How should HbAc measurements be reported? Diabetologia. ;9:-.. American Diabetes Association. Standards of medical care in diabetes. Diabetes Care. ;(suppl):s-s.. Jeppsson JO, Kobold U, Barr J et al. Approved IFCC reference method for the measurement of HbAc in human blood. 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