Analysis of the reasons for differences in APTT results

01、

Activated partial thromboplastingtime (APTT) is a screening test that mimics all the conditions of endogenous coagulation in vivo, determines the defects of factors required for plasma clotting, and is also used for the monitoring of heparin therapy
.

APTT detection principle: at 37 °C, add a sufficient amount of activated contact factor activator (such as white clay, diatomaceous earth, ellagic acid, etc.
) and partial thromboplastin (instead of platelet phospholipids) to the plasma to be tested, and then add an appropriate concentration of calcium ions to the time required for plasma to begin clotting, which is APTT.

How different APTT results vary depending on the activator used in different detection systems?

02.
Case history

In the daily review, the following APTT separately extended results caught my attention,

It is unlikely that women have congenital factor VIII and IX deficiency, and whether there are anticoagulants such as lupus anticoagulants in the body, we know that lupus anticoagulants can cause APTT to prolong alone without bleeding symptoms
.

Looking at the medical records, the patient's female, 54 years old, abdominal pain for more than 5 days, splenomegaly to be investigated, it seems that nothing has been found, but the auxiliary examination column writes that the patient has no obvious abnormalities
in the lower hospital to check liver and kidney function test, coagulation function test, and infectious disease screening.
The patient was newly admitted to the hospital and did not start treatment, what caused the APTT to go from normal to prolonged?

The first thought in my mind may be the difference caused by different detection instruments, will it be so? There are exactly two instruments in the department, APTT 50.
20 seconds is the result of instrument one, and the APTT result is 33.
10s (reference range 22.
2-32.
5) on instrument two, basically normal, the quality control of the two instruments on the day is normal, and the test specimens are abnormal, which seems to be the same as the analysis of the difference in results caused by the detection system of their first impression, in order to avoid errors, they did a different time on another machine in the instrument series and the previous 50.
2s results are consistent
。

We did the APTT correction test, and the results of the correction test are as follows

03.
Case study

The reagent used on the instrument is HemosilSynthAsil, and its activator is colloidal, and its instructions state that the reagent is sensitive
to the concentration of contact factors, endogenous and common pathway coagulation factors.
It is also sensitive to the anticoagulant effect of heparin and the presence of coagulation inhibitors, especially for lupus anticoagulant components
.

The activator used in instrument two machine is ellagic acid, and the sensitivity is not described
much.

According to the instructions written in the instrument, a machine reagent is sensitive to coagulation factors and lupus anticoagulants, what is the reason for the prolongation of APTT in patients?

We did corrective experiments
.
1:1 mixed plasma can be corrected immediately and 2 hours incubation, considering coagulation factor deficiency, the next day was done coagulation factor activity test factor VIII factor 111.
6% (50-150%), IX.
factor 79.
7% (65-150%), factor XI 79.
9% (65-150%), factor XII 19.
00% (50-150%), considering the patient's factor XII deficiency, factor XII is inactive in the blood circulation, blood vessel damage or endothelium damage, its contact with subthelial collagen is activated , activate the endogenous coagulation system
.

Patients have no tendency to bleed on weekdays, and only mild bleeding after surgery or trauma [1], because factor XII can replace factor XII as the initiating factor [2]
when factor XII is deficient.

04.
Summary

APTT reagents produced by different manufacturers have different activators, or the same activators have different intrinsic qualities [3].

Whether the sensitivity of the reagent of the first machine to the detection of factor XII is higher than that of the reagent of the second machine requires more specimen verification
.

In order to reduce the difference between the specimens collected at different times of the same patient due to different detection systems, in daily work, the same patient has been tested on a certain system for the first time on the Lis system of the hospital where the author is located, and the specimens collected at other times are accidentally brushed to another system, which will prompt "The patient's latest coagulation test was performed in the "XXX" group, please switch the group and brush again"
.

【References】

[1] LI Jiazeng, WANG Hongli, WANG Zhaoyue, et al.
Diagnosis and treatment of thrombosis and bleeding[M].
1st edition.
Shanghai:Shanghai Science and Technology Education Press,2003:145-150.
]

Yin Yumei, Bai Jie, Li Fang, et al.
Case analysis and literature review of 1 cases of coagulation factor XII deficiency[J].
Laboratory Medicine and Clinical Medicine,2020,17(15):2264-2266.
)

[3] Wanlagen.
Analysis of results of APTT determination by different reagents[J].
Jiangxi Medical Laboratory Laboratory,2003,21(4):312.
)

[4] Wang Xuefeng, Hu Xiaobo, Cheng Shengli, Xuan Bin, Huang Xiaping, Wang Hongli Comparison of APTT detection reagent sensitivity[J]Chinese Journal of Hematology 2001,22(3)159-160