Effects of storage time and temperature on coagulation tests and factors in fresh plasma

Coagulation tests and factors measurements have been widely applied in clinical practice. Pre-analytical conditions are very important in laboratory assessment.Here,we aim to determine the effects of storage time and temperature on activated partial thromboplastin time (APTT), fibrinogen (Fbg), prothrombin time (PT), the international normalized ratio (INR), thrombin time (TT), factor VIII activity (FVIII:C), and factor IX activity (FIX:C) in fresh plasma. Seventy-two blood samples were tested after storage for 0 (baseline), 2, 4, 6, 8, 12, and 24 h at 25°C (room temperature) and 4°C (refrigeration) in two centers. The mean percentage change of greater than 10% and the numbers of samples with greater than 10% percentage changes more than 25% were used to determine clinically relevant difference. We demonstrated that samples for Fbg, PT/INR, and TT could be safely stored for ≤24 h; FVIII:C for ≤2 h; FIX:C for ≤4 h both at 4°C and 25°C; and APTT for ≤12 h at 4°C and ≤8 h at 25°C.

respectively. Two laboratories with the same analysis system of a Sysmex CA7000 instrument (Sysmex, Kobe, Japan) and Siemens reagents (Siemens, Marburg, Germany) participated in the study.

Results
Between-and within-batch imprecision. Between-and withinbatch imprecision of coagulation tests and factors were all consistent with the manufacturer's product information. Withinand between-batch imprecision were ,3% and 10%, respectively.
Stability studies. Table 1 lists the results and statistical differences of the coagulation tests and factor activities of the plasma samples stored for 2, 4, 6, 8, 12, and 24 h after collection at 25uC and 4uC, compared with the baseline results. Table 2 shows the stability of PT/INR, APTT, Fbg, TT, FVIII:C, and FIX:C when the samples were stored under these conditions.
The mean percentage changes in the values of Fbg, PT/INR, and TT were all less than 10%, and the mean percentage changes in the values of APTT following sample storage for 2, 4, 6, 8, and 12 h at 4uC and 2, 4, 6, and 8 h at 25uC were all less than 10%, compared to the baseline values. However, the mean percentage changes of FVIII:C and FIX:C all exceeded 10%, except FVIII:C storage for 2 h at 25uC and 4uC; FIX:C storage for 2, 4, 6, and 8 h at 4uC; and FIX:C storage for 2, 4, and 6 h at 25uC. Table 2 shows that the numbers of samples with percentage changes greater than 10% for APTT, Fbg, PT/INR, and TT determination were all less than 25% of the samples after storage for 2, 4, 6, 8, 12, and 24 h at 25uC and 4uC, except for APTT determination for samples stored for 12 h at 25uC, and 24 h at 4uC and 25uC. In the cases of FVIII:C and FIX:C, the number of samples with a percentage change greater than 10% for FVIII:C was less than 25% of the samples only after storage for 2 h, and for FIX:C it was after storage for 2 h and 4 h. Furthermore, Figure 1 shows the trend of mean percentage changes of FVIII:C and FIX:C in samples stored for 2, 4, 6, 8, 12, and 24 h at 25uC and 4uC. With extended storage time, at both 25uC and 4uC, FVIII:C and FIX:C were reduced significantly; FVIII:C was even reduced to as low as 49.13% of the baseline value after storage for 24 h at 25uC; meanwhile, FIX:C was reduced to 15.59%.

Discussion
Coagulation tests and factors measurements have been widely applied in clinical practice; therefore, it is necessary to evaluate the effects of temperature and time from collection on the outcome of these results. Our multicenter study investigated the effects of split tube storage for 2, 4, 6, 8, 12, and 24 h at 25uC and 4uC. Of note, this study was the first to investigate the stability of FVIII:C and FIX:C at 25uC and 4uC in fresh plasma. Although many domestic and foreign scholars have studied the effects of pre-analytical variables on coagulation test analysis, no studies have described the stability of FVIII:C and FIX:C at 25uC and 4uC. A summary of these studies is listed in Table 3 2,8,10,12,13,[15][16][17] . Nonetheless, there are no unified guidelines for clinically acceptable bias. Some scholars have suggested the use of mean percentage change to evaluate the stability of coagulation tests and factor determination and have considered a mean percentage change of less than 10% to be clinically relevant [12][13][14] . Moreover, van Geest-Daalderop et al. proposed that if the number of individuals with a greater than 10% percentage change was less than 25% of the total sample number, the effect should be termed moderate and clinically relevant 12 . However, Zürcher 18 suggested that the imprecision may have a greater impact on the results than the changes in stability studies. In this study, to minimize analytical performance variability, we utilized a single assay kit batch for all analyses. We demonstrated satisfactory within-and between-batch imprecision. Thus, using these two methods, clinically important changes in individual and overall samples might be found.
In our study, although significant differences (shown in Table 1) were observed, some biases were still within an acceptable interval. For example, the results of Fbg, PT/INR, and TT determination were clinically relevant after storage for up to 24 h at 4uC and 25uC; while APTT could be stored for up to 12 h at 4uC and 8 h at 25uC. Of note, the acceptable time interval for APTT determination was longer than recommended in the CLSI H21-A5 guidelines. In contrast, the studies of Wang X et al. 8 and Wang BL et al. 15 have shown that the acceptable time intervals for PT and APTT determination are shorter than those recommended in the guidelines. Other studies have suggested that acceptable time intervals for coagulation tests can be extended 13,16,17 . Kemkes-Matthes et al. 13 have reported that PT, APTT, Fbg, TT, AT, and D-dimer can be reliably tested after storage for 8 h at room temperature and that the acceptable time interval can easily be extended to 24 h for PT, TT, and D-dimer determination. van Geest-Daalderop et al. 12 have reported that the acceptable time interval for PT/INR determination is 6 h at 4-6uC, 25uC, and 37uC. Moreover, Oddoze et al. 16 have reported that the acceptable time interval for APTT determination is 6 h at 4uC and 25uC. In addition, Rao et al. 17 have reported that plasma and whole blood samples can be tested for PT for up to 24 h and APTT for up to 12 h, when transported either at room temperature or at 4uC. Although many studies have analyzed the stability of coagulation factor activity in FFP 6,19-21 , very few studies have analyzed fresh plasma. In our study, the acceptable time interval for FIX:C determination was Furthermore, the determination of FIX was also important for the diagnosis of consumption coagulopathy and hepatic cirrhosis 5,22 . Thus, the true activity determination of FVIII and FIX in the patient's plasma was valuable in clinical applications. In Figure 1, we found that FVIII:C and FIX:C were reduced significantly with extended storage time. To avoid FVIII:C and FIX:C becoming lower than the true activity, we carried out a multicenter study, initially reviewed the stability of FVIII:C and FIX:C determination at 25uC and 4uC, and put forward reliable results for clinical diagnosis and treatment. Cardigan et al. 24 showed that storage of whole blood at room temperature for 8 h resulted in a 23% loss of FVIII:C. Thus, the results of FVIII:C determination at 25uC in our study were similar to those presented by Cardigan et al. 24 , and the results of FIX:C determination were shorter than those presented in that same study 24 .
Our multicenter study has some limitations. First, the study was based on asymptomatic individuals. Second, we used only one type of reagent, instrument, and collection container. Our conclusions can perhaps be corroborated by further study based on different study populations, reagents, instruments, and collection containers.
In conclusion, our results demonstrated that plasma samples tested for Fbg, PT/INR, and TT determination could be safely stored for up to 24 h both at 4uC and 25uC; those tested for APTT measurement could be safely stored for 12 h at 4uC and 8 h at 25uC; those tested for FIX:C measurement could be safely stored for 4 h at 4uC and 25uC; and those tested for FVIII:C could be safely stored for only 2 h at 4uC and 25uC, suggesting that FVIII:C should be immediately measured within 2 h after collection in our laboratory. Thus, clinical samples should only be stored for these time frames prior to testing.

Methods
Participating centers. The study was carried out in two laboratories, including the First Affiliated Hospital of Zhejiang University (Center 1) and The First People's Hospital of Hangzhou (Center 2). Both Centers, 1 and 2, used the same blood collection system (Becton Dickinson, Franklin Lakes, USA), Sysmex CA7000 system (Sysmex, Kobe, Japan), Siemens reagents (Siemens, Marburg, Germany), and International Sensitivity Index (ISI, ISI 5 0.99).
Sample size. Sample size estimates were calculated using a post hoc power of analysis with two size effects (0.8/0.9) and alpha levels (0.05/0.1). A sample size of 72 patients (36 per group) was appropriate.
Patients. The study involved 36 asymptomatic individuals who visited the First Affiliated Hospital of Zhejiang University (Center 1) and 36 asymptomatic  Assays. Venipunctures were performed in the morning following a 12-h fast. From each patient, a 5.4-ml venous whole blood sample was collected into a tube containing 0.109 M sodium citrate as an anticoagulant (Becton Dickinson, Franklin Lakes, USA) at a blood to anticoagulant ratio of 951. The 72 samples were centrifuged (10 min, 3000 g) to obtain fresh plasma without platelets and cells, and each sample was divided into 13 Eppendorf tubes and capped. The Eppendorf tubes used for the aliquots were composed of a nonactivating plastic. One split tube was tested immediately, which served as the baseline (0 h) results, while the remaining 12 split tubes were tested, respectively, after storage for 2, 4, 6, 8, 12, and 24 h at 25uC and 4uC. In Centers 1 and 2, the plasma samples were tested by a coagulation method for APTT, PT/INR, TT, Fbg, FVIII:C, and FIX:C using a Sysmex CA7000 system (Sysmex, Kobe, Japan) and Siemens reagents (Siemens, Marburg, Germany): Dade Actin activated cephaloplastin reagent (lot 547713), Dade Thrombin reagent (lot 538065), Thromborel S (lot 545515), Test Thrombin reagent (lot 42780), Coagulation factor VIII-deficient plasma (lot 546576), and Coagulation factor IX-deficient plasma (lot 500870B), respectively. In addition, INR was transformed by PT according to the formula: INR 5 (PT/mean normal prothrombin time) ISI . The compositions of Siemens reagents were liquid rabbit brain cephalin with plasma activator, lyophilized bovine thrombin, lyophilized human placental thromboplastin, lyophilized human bovine thrombin and bovine albumin, and lyophilized human plasma with a residual FVIII:C and FIX:C of #1% for use in the determination of APTT, Fbg, PT, TT, FVIII:C, and FIX:C. The results were expressed in s (PT, APTT, and TT), g/l (Fbg level), and % (FVIII:C and FIX:C).
Two mixed pools having normal and abnormal target results were prepared from freshly collected plasma and were used to measure APTT, Fbg, PT, TT, FVIII:C, and FIX:C 20 times in 2 h to assess within-batch imprecision. Commercial quality control products (SIEMENS) with target results in normal/abnormal ranges were used to measure APTT, Fbg, PT, TT, FVIII:C, and FIX:C on 20 separate days to calculate between-batch imprecision. The manufacturer's product information for the assays claims that between-and within-batch imprecision should be ,15% and ,5%, respectively, for PT, APTT, Fbg, and TT; between-batch imprecision should be ,10% for FVIII:C and FIX:C; and within-batch imprecision should be ,10% (normal) and ,3% (abnormal) for FVIII:C and FIX:C, respectively.