Effect of Delay Separation and Short Term Storage of Serum on Thyroid Stimulating Hormone (TSH)

Abstract

Nepal. A total of 15 individual visited to the immunoassay laboratory for thyroid function test were conveniently selected for this study and fi ve milliliters venous blood samples were collected in a plain vial by venipuncture and divided into two aliquots. First aliquot was centrifuged immediately and serum was separated. Second aliquot was stored at ambient temperature (22 ºc) for 24 hours in a temperature controlled air conditioned laboratory before separation of serum. From the fi rst aliquot, TSH was measured by sandwich ELISA based immunoassay (Eliscan, India) [5] on the same day and remaining aliquot was stored at 4 ºc for 7 days and TSH level was measured after 7 days. Serum was separated from second aliquot after 24 hours and TSH level was measured on the same day. Data was expressed as median (Inter Quartile range) and Wilcoxon Signed Ranks test was applied to test the signifi cance level, considering p value ≤ 0.05 as statistically signifi cant. Result The median (IQR) of baseline serum TSH level was not statistically signifi cant different between delay separated (after 24 hours) sample and short term stored (4 ºc for 7 days) (1.43 (0.18, 6.52) μIU/mL vs 1.61 (0.25, 6.51) μIU/mL, p= 0.069 and 1.43 (0.18, 6.52) μIU/mL vs 1.57(0.26, 5.75) μIU/mL, p=0.925). Discussion This is hospital based quasi experiment to see the effect of delay separation and short term storage on stability of thyroid stimulating hormone. Stability of hormones in a samples are infl uenced by the length of time after collection, storage temperature and the number of freeze-thaw cycles [6]. The rationale of measuring serum TSH level in clinical setting is different from that in epidemiological settings. In clinical settings, measurement used to fi nd out the normal and abnormal values as well as to assess the degree of abnormality but moderate difference with in the reference range are of etiological interest in epidemiological studies [7]. Delays in transportation of blood specimens to the laboratory may cause systematic changes in hormone concentrations and this could obscure association in epidemiological studies [8]. It is not always practical to process blood samples immediately after collection and should be stored for further analysis in large epidemiological as well as in clinical study [9]. In this study, the baseline serum TSH level is not signifi cantly different as compared to delay separated samples and short term stored samples (Table 1). Mannisto T et al. (2007), reported no differences in TSH, fT4, TPO-Ab, or TG-Ab concentrations when 50 frozen and thawed serum samples were compared with 50 fresh serum samples [10]. Allen AL et al. (1997), also reported statistically no signifi cant differences (p=0.7) associated with the measured concentrations of baseline T3 or T4 and serum separated after 24 hours. The effect of long-term storage on T3 and T4 in male and female serum was also reported by Allen et al. (1997), [7]. There were no apparent trends or statistically signifi cant differences in between baseline and 19 to 22 months stored T3 concentrations either in males (p=0.23) or females (p=0.52)12 Jones ME et al. (2007), reported that, 7.1% and 5.6% increase in estradiol concentration after one day and two days delay in processing. Progesterone concentrations showed no substantial change over the two days period but testosterone concentrations increased by 23% after one or two days delay in processing. FSH and LH concentrations increased on average by 7.0% and 3.8% per day respectively. In contrast to this, SHBG concentrations decreased on average by 5.8% per day over the two days period [11]. Oddie TH et al. (1979), reported that, signifi cant decline in T4, rT3, TSH and T3, concentration with storage interval, the mean observed rates of decline correspond to 5.3%, 3.5%, 0.9%, and 4.3% per year, respectively but TBG concentrations did not appear to change signifi cantly during storage [12].