Matrix Selection for Measurement of Zinc Levels

INTRODUCTION: Measurement of blood zinc levels is frequently used in the diagnosis of a few conditions such as growth retardation, immunodeficiency, infertility, neurological disorder, and acrodermatitis enteropathica. The serum matrix is the most preferred one to determine zinc levels due to the ease of analysis with other tests and cost-effectiveness of blood collection tubes used to obtain serum samples. In our study, we aimed to compare serum and plasma zinc test results for accurate and reliable zinc measurement in plain tubes with clot activator and gel and in heparin-free tubes, which specifically produced for trace element analysis.
METHODS: Twenty-seven randomly selected patients were included in the study. Blood samples drawn simultaneously from patients were pipetted into tubes with clot activator and gel (SST) (SST II Advance, Vacutainer, Becton Dickinson and Company, USA) as well as into trace element tubes with sodium heparin (NH) (NH Trace Elements Sodium Heparin, Vacuette, Greiner Bio-One GmbH, Austria). After the centrifugation process, zinc levels in serum and plasma samples were analyzed by colorimetric method using an autoanalyzer. Bias between serum and plasma zinc levels was evaluated according to the allowable bias criterion based on biological variation and regression analysis performed.
RESULTS: The mean and standard deviation of serum and plasma zinc levels were 49.0±11.5 μg/dL and 46.4±12.0 μg/dL, respectively, and a statistically significant difference was determined (p=0.012) in between. Besides, the bias between serum and plasma was 6.8%, which was above the allowable bias (3.3%) and considered as clinically significant. No systematic or random errors detected.
DISCUSSION AND CONCLUSION: When selecting a blood collection tube for trace element analysis, the structural differences between tubes and the matrix effect should be considered carefully.

Çinko Düzeylerinin Ölçümünde Matriks Seçimi

GÝRÝÞ ve AMAÇ: Çinko, büyüme geriliði, immün yetmezlik, infertilite, nörolojik bozukluk, akrodermatitis enteropatika tanýsý gibi durumlarda sýklýkla kullanýlan bir testtir. Çinko düzeylerinin ölçümünde diðer testlerle birlikte analiz edilme kolaylýðý ve serum eldesinde kullanýlan kan alma tüplerinin maliyet etkinliði nedeniyle sýklýkla serum matriksi tercih edilmektedir. Çalýþmamýzda doðru ve güvenilir çinko sonuçlarý için standart pýhtý aktivatörlü jelli ve eser element için özel üretilmiþ heparinli jelsiz tüplerdeki serum ve plazma çinko sonuçlarý karþýlaþtýrýlmasý amaçlanmýþtýr.
YÖNTEM ve GEREÇLER: Çalýþmaya rastgele seçilmiþ 27 hasta dahil edildi. Hastalardan eþ zamanlý hem pýhtý aktivatörlü jelli tüplere (SST) (SST II Advance, Vacuteiner, Becton Dickinson and Company, Amerika), hem de sodyum heparin içeren eser element tüplerine (NH) (NH Trace Elements Sodium Heparin, Vacuette, Greiner Bio-One GmbH, Avusturya) kan alýndý. Santrifüj sonrasý elde edilen serum ve plazma örneklerinde çinko düzeyleri kolorimetrik yöntem ile otoanalizörde ölçüldü. Serum ve plazma çinko düzeyleri arasýndaki bias biyolojik varyasyon kaynaklý izin verilebilir bias kriterine göre deðerlendirildi ve regresyon analizi yapýldý.
BULGULAR: Serum ve plazma çinko düzeylerinin ortalamasý ve standart sapmasý sýrasýyla 49.0±11.5 μg/dL ve 46.4±12.0 μg/dL olarak bulundu ve arasýnda istatistiksel olarak anlamlý fark saptandý (p=0.012). Ayrýca serum ve plazma arasýndaki bias %6,8 olup, izin verilebilir biasýn (%3,3) üzerindeydi ve klinik olarak anlamlý kabul edildi. Sistematik ya da rastlantýsal hata saptanmadý.
TARTIÞMA ve SONUÇ: Eser elementler ölçümü için kullanýlacak kan alma tüpleri seçilirken yapýsal farklýlýklar ve matriks etkisi nedeniyle oluþabilecek farklýlýklar göz önünde bulundurulmalýdýr.