No clinically relevant differences between capillary and venous blood cell counts in adult haematological patients using a nonautomated lancet

Sir, Physicians who treat patients suffering from haematological diseases require the determination of peripheral complete blood counts (CBC), among other tests, for making day-to-day therapeutic decisions. Venous values are accepted as the standard. The most common access site is a superficial arm vein. This situation can create problems: difficulty in finding a site for punctures, repeated attempts with considerable pain, phlebitis, haematoma and inadequate sampling. For these reasons, capillary CBC through finger pricking has been used an alternative in patients with blood sampling difficulties, particularly in infants and children. The successful use of this approach has been reported previously by many authors [1–6]. Samples are easily obtained and the results are quickly available, and trials from the last 10 years agree with the fact that capillary and venous blood CBC results are similar in both adults with haematological diseases and healthy controls; however, the procedure requires the use of an automated lancet to avoid operator mistakes. This procedure is painful, and the cost of the automated lancet is higher than that of a generic one. To our knowledge, there is no information regarding capillary vs. venous blood cell count in haematological patients using a nonautomated lancet. This prospective, comparative, single-arm study was performed between March 2013 and February 2014 in patients with haematological diseases who came to the haematology service of the University Hospital ‘Dr. Jos e Eleuterio Gonz alez’ in Monterrey, Mexico, for routine medical evaluation. Eligible patients were 18 years or older. Participants were excluded if they had an active infection, positive serology for HIV, hepatitis C, or B infections or were pregnant. Our institution’s ethics committee approved the study protocol, and all patients gave written informed consent before any procedure. Our primary outcome was the comparison between capillary and venous blood cell counts. Two blood samples were obtained from each patient at the same time; the first sample was obtained by puncture of a finger and the second sample was obtained by puncture of the antecubital vein. The procedure consisted in a finger prick on the lateral aspect of the pulp of the third or fourth finger of one hand, using a safety lancet (mediLance 3 mm blade, Monterrey, M exico); the first drop of blood was discarded to minimize excess tissue fluids. An aliquot of 200–500 lL of blood was collected in a tube with ethylenediaminetetraacetic acid (EDTA) for anticoagulation (BD Microtainer, NJ, USA). If necessary, the finger was gently massaged to obtain the required volume. Venous blood was procured from an antecubital vein into a vacuum tube (5 mL BD Vacutainer, Armonk, NY, USA) with EDTA. The punctures were performed by three operators (medical technicians) who attended the patients randomly. The same operator took capillary and venous blood samples from each subject. Both samples were assessed using the haematology analyser Sysmex XT-2000i (Sysmex, Kobe, Japan). Results are presented as means with standard deviation, among other central tendency measures. Venous and capillary measurements were contrasted according to the normality in the Kolmogorov–Smirnov test using either Student’s t-test or analysis of variance (ANOVA) for paired samples. Correlations between capillary and venous samples were determined using Spearman or Pearson’s tests according to the normality as well. Cohen’s kappa was obtained in order to compare each sample’s ability to diagnose low, normal or high values in each variable according to our laboratory’s reference values. Table 2 notes. Specificity was calculated by dividing ‘true-negative’ capillary results (i.e. normal capillary results confirmed in venous testing) by all negative results in the venous sample. The relation between ‘truepositive’ (i.e. altered capillary results confirmed in venous testing) and all altered venous values determined sensitivity. A P-value of 0.05 was considered significant, and all tests were two-sided. Statistical analysis was performed using SPSS software version 20.0 for Mac (IBM, Armonk, NY, USA). We included 107 patients, 15 were excluded from the analysis; three were considered healthy and 12 because their samples were taken by two different operators. Ninety-two patients were analysed. The median age was