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Routine coagulation testing: do we need a discard tube?
1Clinical Haematology, Haemato-Oncology and Bone Marrow (Stem Cell) Transplant Unit, Christian Medical College & Hospital, Ludhiana, Punjab India.
Insights
Discard tubes may not be necessary for coagulation testing. This study found no significant difference in Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) results between the first and second tubes drawn, suggesting comparable accuracy.
Area of Science:
- Hematology
- Clinical Pathology
- Laboratory Medicine
Background:
- Current guidelines recommend using a discard tube for coagulation tests.
- This practice is inconsistently followed, with many labs using a single tube draw.
- Previous research suggests comparable results can be obtained from both tubes in a two-tube draw.
Purpose of the Study:
- To evaluate the necessity of discard tubes in routine coagulation testing.
- To compare Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) results from the first and second tubes in a two-tube draw.
- To assess the clinical applicability of omitting discard tubes in coagulation analysis.
Main Methods:
- Prospective study conducted over 3 months in a North Indian tertiary care teaching institution.
- Fifty-six paired blood specimens were collected from healthy volunteers using a two-tube draw method.
- Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) were analyzed within 1 hour using a fully automated coagulation instrument (Ceveron-Alpha).
- Paired results were compared using Bland-Altman plots for method comparison.
Main Results:
- Good correlation was observed between PT, INR, and APTT values from the first and second tubes.
- Bias values were 0.09 for PT, -0.05 for INR, and 0.3 for APTT.
- Bland-Altman analysis showed acceptable agreement, with 95% confidence intervals indicating minimal variation between tubes.
Conclusions:
- No significant difference was found between PT and APTT values obtained from the first and second tubes.
- The use of a discard tube is not required for routine coagulation testing.
- This finding supports simplifying laboratory procedures and potentially reducing blood draw volume.
Abstract:
When coagulation tests are performed, the recommended guideline is that a discard tube be used and the coagulation testing should be done only on the second tube. This guideline is however inconsistently enforced and most laboratories follow a single tube draw for routine coagulation testing. Few studies have however, challenged this guideline and have shown that comparable results can be obtained in both tubes when a two tube draw is used. This prospective study was done over a 3 months period in the hematology laboratory under the Clinical Hematology unit of a tertiary care teaching institution in North India. Fifty-six paired specimens were drawn from healthy volunteers following the prescribed "two tube draw" method. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were performed within 1 h of sample collection on a fully automated photo-optical coagulation instrument (Ceveron-Alpha). Paired results for PT and APTT were compared using Bland-Altman plots for method comparison. There was good correlation between the PT, INR and APTT of the first and second tubes with bias of 0.09, -0.05 and 0.3 respectively). Bland-Altman plots showed acceptable agreement between the two values with 95 % confidence interval ranging from -0.62 to 0.79 for PT, -0.05 to 0.06 for INR and -3.9 to 4.6 for APTT. Our study has shown no significant difference between PT and APTT values for the first and second tubes. Hence the use of a discard tube is not required.
