PB0154 - Unmeasurable Activated Partial Thromboplastin Time in Routine Coagulation Screening – Was it pre-analytical?

Background: The CS-2500 is a mid-volume coagulation analyser that performs in-vitro coagulation tests using photo-optical principle. Apart from pre-analytical sample-quality checks feature, the analyser can illustrate the clot reaction profile during Prothrombin Time (PT) and Activated-Partial Thromboplastin Time (APTT) testing through its clot curve analysis. Regardless of these specified features, we found that PT and APTT were not simultaneously measured on several occasions and this initiated us to investigate further.

Aims: To investigate the causes of unmeasurable APTT in routine PT/APTT testing and to evaluate the possibility of pre-analytical issues that could cause unmeasurable APTT testing.

Methods: This retrospective study of PT/APTT testing between January 1, 2023 to December 31, 2023 with unmeasurable APTT was identified. The analytical flags produced by the analyser were extracted. The subsequent PT/APTT results of the affected patients’ samples were reviewed.

Results: Out of 8,266 PT/APTT testing, there were 28 (0.3%) cases of unmeasurable APTT from 25 patients. Of these, 24 cases generated specific analytical error flag of ‘no coagulation’ (NC) and 4 cases produced ‘early reaction error’ (ERE) flag. Majority of the cases (21/28) only required one subsequent sample compared to 3/28 that required more samples to finally obtain APTT results. 4 cases of NC however did not have subsequent sample. The NC samples presented with normal APTT (10/20) and prolonged APTT (10/20) on the subsequent samples, while all samples with ERE flag gave prolonged APTT.

Conclusion(s): Approximately 58.3% of unmeasurable APTT cases returned with prolonged APTT while 41.7% returned with normal APTT. The prolonged APTT samples originated from wards which are known in administrating high dose heparin. Meanwhile for the normal APTT group, the unmeasurable APTT during the first sampling perhaps were due to pre-analytical issue during blood sampling which the phlebotomists were not aware of. In conclusion, the coagulation analyser's flags facilitate in-depth investigations on clinical samples.