|Year : 2022 | Volume
| Issue : 2 | Page : 41-46
Effect of varying storage time and temperature on unspun blood samples for prothrombin time and activated partial thromboplastin time in a tertiary hospital laboratory in the tropics
Ann A Ogbenna1, Oluwafikewa A Oyedele2, Titilope A Adeyemo1, Kunmi Mathew Oyewole3
1 Department of Haematology and Blood Transfusion, College of Medicine, University of Lagos and Lagos University Teaching Hospital, Idi-Araba, Lagos, Nigeria
2 Department of Haematology and Blood Transfusion, College of Medicine, University of Lagos, Idi-Araba, Lagos, Nigeria
3 Department of Haematology and Blood Transfusion, Lagos University Teaching Hospital, Idi-Araba, Lagos, Nigeria
|Date of Submission||28-May-2021|
|Date of Decision||26-Aug-2021|
|Date of Acceptance||21-Oct-2021|
|Date of Web Publication||22-Aug-2022|
Dr. Oluwafikewa A Oyedele
Department of Haematology and Blood Transfusion, College of Medicine, University of Lagos, Idi-Araba, Lagos State
Source of Support: None, Conflict of Interest: None
Introduction: Delays in the time of analysis of unspun blood samples stored at varying temperatures received in the laboratory pose a risk for unreliable prothrombin time (PT) and activated partial thromboplastin time (APTT) result; hence, consequent detrimental effect on patient care. This study's aim was thus to determine the optimal storage conditions and the potential effect of various storage times and temperatures on unspun samples for PT and APTT for a reliable test result. Materials and Methods: In a cross-sectional study, 33 eligible apparent healthy volunteers were recruited. Eighteen milliliters (ml) of venous blood were collected into 20 ml plastic bottles containing 2 ml of 0.109 M sodium citrate as an anticoagulant. Each citrated sample was separated into nine 2 ml aliquots. Baseline PT and APTT were determined with a coagulometer immediately and the remaining aliquots were analyzed after 3, 6, 12, and 24 h storage time at refrigerated (4°C) and room temperature (RT), respectively. The Statistical Package for the Social Sciences and Paired student t-test were used for statistical analysis. Results: At 24 h storage time at both RT and 4°C for PT, there was a statistically significant difference (P = 0.000). For APTT, a statistically significant difference was observed at 12 h (P = 0.009) and 24 h (P = 0.000) at RT whereas, at 4°C, all storage time had a statistically significant difference (P < 0.05). Conclusion: Unspun blood samples can be stored maximally for 12 h at RT and 4°C for PT whereas it is 6 h at RT only for APTT.
Keywords: Activated partial thromboplastin time, preanalytical variables, prothrombin time
|How to cite this article:|
Ogbenna AA, Oyedele OA, Adeyemo TA, Oyewole KM. Effect of varying storage time and temperature on unspun blood samples for prothrombin time and activated partial thromboplastin time in a tertiary hospital laboratory in the tropics. Sahel Med J 2022;25:41-6
|How to cite this URL:|
Ogbenna AA, Oyedele OA, Adeyemo TA, Oyewole KM. Effect of varying storage time and temperature on unspun blood samples for prothrombin time and activated partial thromboplastin time in a tertiary hospital laboratory in the tropics. Sahel Med J [serial online] 2022 [cited 2023 Jun 3];25:41-6. Available from: https://www.smjonline.org/text.asp?2022/25/2/41/354187
| Introduction|| |
Prothrombin time (PT) and activated partial thromboplastin time (APTT) are sensitive coagulation tests frequently ordered together by physicians to evaluate hemostatic disorders. In many clinical practices, samples collected for these tests are transported to the laboratory for undetermined but variable periods after collection. Transport delays may prolong clotting times and in vitro loss of factor activity, especially the labile factors FV and FVIII.
Hence, this study is designed to investigate the potential effect of storing citrated whole blood at varying temperatures and times on coagulation tests. Moreover, to determine the optimal storage conditions for a reliable test result.
| Materials and Methods|| |
A cross-sectional study was carried out in November 2019 in the hematology laboratory of Lagos University Teaching Hospital (LUTH), Lagos State, Nigeria. LUTH is a tertiary hospital established in 1962 affiliated with the University of Lagos.
Staff and students of LUTH within the period of the research were recruited after obtaining informed consent. Thirty-three apparently healthy adult volunteers ages 18–65 years were recruited. Exclusion criteria included those that did not fall within the age range, were pregnant, people who had breakfast (high in fats), unease due to strenuous exercise, and on any medication (anticoagulant, heparin, and contraceptive).
The sample size was calculated using power and sample size calculations software version 2.1.31 PlayStation store program for paired test formula with 95% confidence interval. Standard deviation σ = 4.0 according to the literature for paired test formula, desired precision δ = 2 with power 80% was used.
A trained phlebotomist performed venepunctures in the morning following a 12-h fast. From each participant, 18 ml venous whole blood sample was collected into plain bottles containing 2 ml of 0.109 M sodium citrate as an anticoagulant at blood to an anticoagulant ratio of 9:1. Samples were mixed thoroughly (but gently) by 3–6 end over end tube inversions to ensure adequate mixing of the test sample with the anticoagulant. Afterward, the following steps were carried out to each sample:
- The blood sample collected was aliquoted evenly into nine plain bottles labeled B0, R3, R6, R12, R24, F3, F6, F12, and F24 in addition to the participant study number
- Bottles labeled B0 were tested immediately for baseline result of PT and APTT
- Bottles labeled R3, R6, R12, and R24 were stored at room temperature (RT) of 25°C for 3 h, 6 h, 12 h, and 24 h, respectively
- Bottles labeled F3, F6, F12, and F24 were stored at 4°C for 3 h, 6 h, 12 h, and 24 h, respectively.
Each sample bottle was centrifuged at 2500 g for 10 min after storage of 3, 6, 12, and 24 h, respectively, including bottle B0 which was not stored. Afterward, the platelet-poor plasma (PPP) obtained was assayed for PT and APTT using a semiautomated blood coagulation analyzer (Sysmex CA-10, Ahrensburg, Germany).
PT and APTT reagents; Dade Innovin (LOT 549750C), actin FS (LOT 538552), calcium chloride (LOT 563857) were obtained from Sysmex. PT was determined by preincubating 50 μl of PPP for 30 s at 37°C in the semiautomated coagulometer (Sysmex). The coagulation reaction was then initiated by the addition of the 100 μl Dade Innovin (LOT 549750C). The endpoint result in seconds is displayed when a clot is formed.
For APTT, 50 μl of the PPP is preincubated with 50 μl of actin FS (LOT 538552) for 180 s at 37°C in the semiautomated coagulometer (Sysmex). The coagulation reaction is initiated by the addition of 50 μl of calcium chloride (LOT 563857), and the machine displays the endpoint result in seconds when a clot is formed.
Normal and pathological controls were run for every vial of reagent used. Furthermore, APTT and PT measurements were performed in duplicates and three or four times for that samples, which had a difference of more than 1 s, the final values, were the mean of the results.
Data obtained were analyzed using the Statistical Package for the Social Sciences (SPSS) version 22 (IBM Corp., Armonk, NY, USA). Paired student t-test with confidence intervals of 95% was used for comparison between the results at different time intervals with 0 h. Results were expressed as mean values and giving other descriptive statistics. A P ≤ 0.05 was considered significant in all statistical comparisons. To assess stability, the mean percentage changes (result at storage time X– Result at baseline, divided by results at baseline, expressed as a percentage change) compared with the baseline results were calculated and represented graphically. The clinically relevant difference was defined as a percentage change of greater than (>) 10% according to van geest. The effect of a clinically relevant difference >10% observed in <25% of the samples was termed moderate whereas when observed in >25% of the samples was termed large.
Approval of this study (ADM/DCST/HREC/APP/3260) was obtained from LUTH health research ethics committee before the commencement of the study.
| Results|| |
Biodata of study
The mean age of the study population was 34.42 years of which the majority were within the age range 40–44 years (30.3%). There was a high prevalence of males (63.6%) as to the female (36.4%).
Effect of varying storage time and temperature on prothrombin time
[Table 1]a and [Table 1]b show the effect of varying storage time on PT the PT result at RT and 4°C, respectively. The mean PT result (baseline) was 14.22 s which was within the normal range (12.6–17.2 s) of PT in Nigeria.
The mean PT at 24 h at RT had a statistically significant difference (P = 0.000) as shown in [Table 1]a. At 3 h, 6 h, and 12 h, the mean PT was not statistically different from baseline PT (P > 0.05).
A similar trend was observed in the PT results at 4°C storage in [Table 1]b as in the PT RT storage times. A statistically significant difference (P = 0.000) was observed at 24 h storage time.
Effect of varying storage time and temperature on activated partial thromboplastin time
The APTT results at RT and 4°C are shown in [Table 2]a and [Table 2]b. The mean APTT result (baseline) was 30.24 s which was within the normal range (26.92–33.1s) of APTT in Nigeria.
At RT, a statistically significant difference was observed at 12 h (P = 0.009) and 24 h (P = 0.000) storage time as shown in [Table 2]a. However, at 4°C at all the storage times 3, 6, 12, and 24 h a statistically significant difference (P < 0.05) as shown in [Table 2]b.
Stability studies of prothrombin time and activated partial thromboplastin time
The stability of the PT and APTT assay was investigated using the mean percentage change from baseline at the different storage times and temperatures as shown in [Figure 1].
|Figure 1: Mean percentage change in prothrombin time/activated partial thromboplastin time from baseline over time|
Click here to view
The mean percentage change for PT at both RT and 4°C were all positive following a 3, 12, and 24 h storage. A negative change was observed at 6 h storage at both RT and 4°C. On the other hand, the mean percentage for APTT at both RT and 4°C were all positive except at 3 h storage at RT.
[Table 3]a and [Table 3]b show the range of positive and negative differences from the baseline result observed in the PT and APTT results, respectively.
For PT at RT, the percentage of samples with positive changes that exceeded the 10% limit was moderate (<25% of sample size) after 3 h, 6 h, and 12 h and large (>25% of sample size) after 24 h as shown in [Table 3]a. At 4°C, the percentage of samples with positive changes that exceeded the 10% limit was moderate (<25% of samples) at 6 h storage time and large (>25% of samples) at 3, 12, and 24 h.
The result from [Table 3]b at RT APTT shows that the percentage of samples with positive changes that exceeded the 10% limit was moderate (<25% of samples size) at 3 h and 6 h storage. At 12 h and 24 h storage the effect was large (>25% of sample size).
Whereas at 4°C, the percentage of samples with positive changes that exceeded the 10% limit was moderate (<25% of samples) at 6 h storage time and large (>25% of samples) at 3, 12, and 24 h.
| Discussion|| |
The result of this study demonstrates that the storage time and temperature affect routine screening coagulation test PT and APTT. For PT, the changes observed at 3 h, 6 h, and 12 h were not statistically significant but were clinically relevant with moderate to large effect. However, at 24 h of storage at both RT and 4°C, the results were both statistically significant and clinically relevant with large effect.
Contrarily, the results of APTT showed that the maximum storage time as unspun blood was 6 h at RT. After 6 h of storage, a statistically significant difference was observed. Moreover, storage at the refrigerator is unacceptable as all the results were statistically significant with clinical relevance of large effect.
The findings of this study when whole blood was stored unspun was in partial agreement with that of a previous study done by Salvagno et al., which reported that APTT can be stored uncentrifuged for 6 h at RT but in variance with 6 h storage for refrigerated sample. In addition, Oddoze et al., evaluated the potential stability of APTT at 6 h and 24 h and states that the acceptable delay time for whole blood samples for APTT 6 h at RT which is in line with the findings of this study. However, their finding of APTT stability at 6 h storage at 4°C contradicts the result of this study.
Furthermore, similar studies on unspun samples by van Geest-Daalderop et al. is in variance with the result of this study. They reported that the optimal storage of whole blood samples for PT/INR is 6 h. This is shorter than our findings of 12 h this could be attributed to the fact that the study evaluated 3 h., 6 h, and 24 h. Moreover, their study sample was patients on anticoagulant therapy whereas this study involved healthy individuals, not on an anticoagulant.
A study by Toulon et al. in France investigated four storages that are, below 2, 4, 6, and 8 h on both healthy and patients on vitamin K-antagonists, at a RT in the range between +18 and +25°C. Their result report on the maximal storage time at +25°C of unspun blood samples for the determination of PT/INR and is APTT is 8 h. This storage time is shorter than this study result for PT, which is 12 h and higher APTT maximum storage of 6 h at RT. The short storage time investigated for PT could be attributed to their conclusion of maximum storage time for PT. On the contrary, Rao et al. report samples stored as whole blood can give a reliable result with a maximum storage of 24 h for PT and 12 h. For APTT at 4°C and RT. However, statistical analysis of the 24 h storage result at RT and 4°C for PT was statistically significant (P = 0.000) in this study. In addition, the 12 h storage for APTT at RT and refrigerator were statistically significant.
The variation to this study highlighted earlier could be due to variation in the population sample used in the study and the times investigated. Similar studies carried out on PT and APTT using plasma storage at different storage conditions report a longer storage time for PT as 24 h ,,, while some reported shorter storage time of 2 h, 4 h, and 12 h. Nevertheless, this study was on whole blood storage at different storage conditions; hence, no statement can be made about the optimal storage conditions on plasma storage. An additional limitation of this study was that this study investigated only the effects of RT and 4°C on PT and APTT for up to 24 h and healthy participants not on heparin or warfarin therapy. Thus, no statement can be made about the effects of these storage conditions, time, and temperature on such samples.
| Conclusion|| |
An inference from this study using healthy individuals shows that the PT result was reliable only within 12 h of storage of unspun blood samples at both 4°C and RT. After which further storage time elicit a statistically significant difference with clinical relevance. On the other hand, the APTT result was reliable within 6 h storage as unspun blood at RT. At 4°C, all storage times after phlebotomy showed a statistically significant difference. Hence, this study recommends that unspun blood samples for PT and APTT be stored for a maximum of 6 h as physicians often request these tests together. In addition, more studies need to be carried out on unhealthy populations as this study was limited to only healthy Individuals.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]