Author: Zhang Xia
Unit: Chongqing Zhongxian Traditional Chinese Medicine Hospital
There are many test items of coagulation factors, of which six are the most common, including APTT, PT, TT, FIB, FDP, and D-dimer.
APTT is currently the most commonly used screening test to detect endogenous coagulation systems to monitor treatment with unfractionated heparin, and PT is an ideal screening test for exogenous coagulation pathways that can be used for monitoring oral anticoagulant therapy.
Case after
An abnormal result was found at 8 a.m., aptt could not detect it (my department used a Hysenmethorn coagulator, the upper limit of APTT detection was 180s), and the TT abnormality was increased by 66.90s (normal 14-21s), as shown in Figure 1 below.
Figure 1
With the original blood retest, APTT still can not detect. The blood is mixed upside down and evenly observed with the naked eye, and there is no phenomenon of agglutination of blood to determine that there is no consumption of a large amount of fibrinogen.
Notify the clinic to re-draw blood for re-examination. Generally, the re-examination of blood is to exclude the wrong patient's blood. The blood that was re-drawn at 10 o'clock was sent for test again, and the results are shown in Figure 2 below.
Figure 2
Blood typing and routine tests of both copies of blood are performed immediately to rule out the wrong patient's blood. why?
Contact your doctor immediately to report the results of six coagulation tests with two significant gaps in a short period of time and ask if there was any treatment related to thrombosis and hemostasis before the blood was drawn. The response was due to the patient's admission to the hospital for COPD, abnormal coagulation function, and hypercoagulable blood clots, and venous blood drawn after using nacroxaparin in the morning.
The answer is found here, heparin binds to antithrombin III (AT) in the body. According to the mechanism of coagulation waterfall, because heparin combined with AT acts on Xa and II.a will affect the detection of coagulation items, especially causing APTT and prolongation of TT, and heparin is naturally degraded after a few hours in the body, so when the second blood is re-examined, the results are restored. The results of the last three times are shown in Figure 3 below.
Figure 3
Case studies
1. The patient draws blood immediately after using heparin, and the heparin content in the blood is very high at this time, which will especially affect the prolongation of APTT and TT. The PT reagent contains heparin antagonists, so the effect will be smaller. In fact, in theory, APTT prolonged the first re-examination to confirm the exclusion of heparin contamination [1].
Therefore, for thrombotic patients after the use of heparin, if the six items of blood clotting should be noted to pay attention to the degradation cycle of heparin, timely blood draw monitoring, but it should be noted that the preventive dose of heparin does not affect the activated APTT [2].
2. Theoretically, heparin will induce the reduction of platelets (HIT), and the occurrence of HIT is related to the immune complex formed by the combination of platelet 4 factor and negatively charged polymer molecules, especially heparin side chains, mainly through exposure to heparin, especially ungraded heparin. It is clear that HIT is caused by IgG antibodies that activate platelets [3]. Activation of platelets induces the aggregation of platelets, resulting in a decrease in platelet consumption. Therefore, it is recommended to monitor the platelet count simultaneously throughout the treatment of heparin.
summary
In daily work, you often encounter critical values, and you can reasonably explain when you encounter completely different results in the work when you report to the doctor, know the source of the critical value, have a sense of traceability, and encounter completely different results like the previous short period of time in the work.
Communicate with clinicians in relevant departments on "Testing for Common Interference Factors and Countermeasures" to improve clinicians' ability to identify interference results. So that when you encounter clinically inconsistent or controversial results, you know what the possible factors are, rather than simply attributing it to the inaccurate laboratory test results.
【Reference】
[1] Editor-in-Chief Shang Hong, Wang Yusan, Shen Ziyu, National Clinical Laboratory Operating Procedures, Fourth Edition, p. 97, People's Medical Publishing House, 2012
[2] Instructions for subiclin (natraheparin calcium injection).
[3] Chen Zhu, Chen Saijuan, Williams Hematology, 9th Edition, p. 1843, People's Medical Publishing House.
Edited by: Yeah Reviewer: Xiao Ran