Impact of Haemolysis in Accuracy of PT/APTT
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Published: Mon, 14 May 2018
Topic: Impact of haemolysis in accuracy of PT/APTT (Important of fast and accurate PT/APTT results in managing patients)
CHAPTER 2: LITERATURE REVIEW
2.1 PT and APTT
Theprothrombin time(PT) and its derived measures ofprothrombin ratio(PR) andinternational normalized ratio(INR) are measures of the extrinsic pathway of coagulation [3, 7]. They are used to determine the clotting tendency of blood, in the measure of warfarin dosage, liver damage, and vitamin K status. PT measures factors I (fibrinogen),II (prothrombin), V, VII, and X. It is used in conjunction with the activated partial thromboplastin time (APTT) which measures the intrinsic pathway [3, 6, 7].
The activated partial thromboplastin time (APTT) test the intrinsic and common coagulation pathways [3,6,7]. Calcium is added to a plasma sample along with phospholipid (a platelet substitute) and kaolin. It was designed to detect deficiencies in VIII, IX and XI. It is used primarily to monitor lowdose heparin therapy, such as for interventional radiology or vascular surgery (<5000 IU heparin) [3, 6]. Historic name for the activated partial thromboplastin time is kaolin cephalin clotting time(KccT) .
2.2 Clinical Aspect of Coagulation
Haemostasis is a cessation of bleeding following injury as a result of complex physiological cascade . Lab based coagulation test should able to provide the clinician access to real-time information, eliminating the need for empirical treatment due to long turn-around time as a result of haemolysed specimen to be rejected for coagulation tests . There are numerous tests currently available and they allow the patient specific dynamic adjustment of treatment, especially in terms of blood transfusion . One of the aims of the laboratory tests is to reduced turn-around times which allow patient-specific tailoring of necessary intervention . Hypercoagulable diseases and inherited bleeding diathesis should be recognized and managed as the disease remains a source of patient morbidity . A heterogeneous group of disorders with unpredictable coagulation effects is seen in liver disease . Looking at the pathophysiological aetiology, transfusion-induced coagulopathy, dilution and trauma; is described are rationale for treatment .
2.3 Phlebotomy Issues and Quality Improvement in Results of Laboratory Testing
The results of laboratory testing often strongly influence medical diagnoses and therapies which laboratory testing play an integral part of the decision-making process [14, 15]. There is a long history of quality requirements in laboratory medicine, which have mainly concerned the analytic phase of this process . There is increasing evidence that further quality improvements should be targeted to extra-analytic phases of laboratory testing due to the substantial advances in technology, be it laboratory automation or analytic quality, . Objective difficulties to monitor most of the pre- analytic variables which lie outside the direct control or supervision of the laboratory personnel, such as phlebotomy, call for effective educational and preventive policies . Lack of understanding about good laboratory practices due to high personnel turnover rates, and inadequate training has contributed to phlebotomy issues . There are several opportunities for making errors during phlebotomy, which mainly concern collection of haemolysed specimen [14, 15]. The haemolyzed sample can interfere with many coagulation factor and is inappropriate for coagulation test [14, 15]. The chance of obtaining specimens of consistent quality may enhance, with favorable revenues for the health care system and the patient’s outcome as a result of improved standardization of phlebotomy techniques, along with operative guidelines dissemination, certification, continuous education, and training of health care professionals involved in blood drawing responsibilities .
2. 4 The effect of haemolyzed specimen in error of PT and APTT test
Laboratory testing provides essential information used by physicians in medical decision making with an estimated 60–70% of these decisions based on laboratory test results [1,2]. The Clinical and Laboratory Standards Institute, in its guidelines for coagulation test like activated partial thromboplastin time (APTT) and prothrombin time (PT) testing, it states that samples with visible haemolysis should not be used. This is because of possible interference with end point measurement interference by clotting factor activation . No mechanism is stated, but one speculation is that exposure of anionic membrane phospholipids during erythrocytolysis could provide a phospholipid-rich surface to accelerate coagulation reactions and, hence, shorten the assay result . Alternatively, prolongation of the test result has been shown in some hemolyzed tubes with speculation that exposure of membrane phospholipids could compete with thromboplastin for activated factor VIIa (FVIIa) availability and have the converse effect .
2. 5 Important of fast and accurate PT/APTT results in managing patient
A haemolyzed specimen that occurs during the entire testing process, from ordering tests to results reporting, and in any way influences the quality of laboratory services . The rejection of hemolyzed specimens causes, at a minimum, inconvenience and could result in delay in clinical decision making with implications for patient care [9, 14]. Moreover, an additional cost is incurred per re-collected specimen, adding to the overall cost of laboratory operation . Moreover, the haemolyzed sample may be evident in each phase of the testing process pre-analytical, analytical and post-analytical . The pre-analytical phase refers to all of the steps from the time of test ordering by the physician until the sample is ready for analysis; the analytical phase includes the actual specimen analysis, and the post- analytical phase encompasses test reporting and interpretation . The pre- analytical phase is also a complex process, encompassing steps that occur outside as well as inside the laboratory (refer to table 1). Even a mild degree of haemolysis may influence test results for PT/APTT result by falsely lowering PT/APTT levels and thus may not present an accurate picture of the patient’s condition .
In a nutshell, haemolyzed blood samples create significant delays in the treatment and disposition of patients in the emergency department . This has multiple clinical implications . Haemolysis of red blood cells during the coagulation specimen collection process leads to a falsely low test result as the spillage of red blood cell contents activates the clotting mechanism . For example, a PTT may actually be 41 seconds, but a haemolyzed sample may show a abnormal result. In general, redrawing a blood specimen extends our disposition time by 45 to 60 minutes on average . This leads to increased time to treatment and disposition, patient and staff dissatisfaction, higher facility costs, and extended waiting times for patients yet to be seen [13,14]. This result of PT and APTT is critical and false high or low in result reporting may affect patient safety which cannot be ignored .
Pre-analytical phase outside the laboratory
Pre-analytical phase in the laboratory
Transport sample to lab
Receive sample in lab
Prepare sample for testing
Transport sample to lab section
-Send sample to appropriate lab section
Table 1 Complexity of the pre-analytical phase
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