title: Routine coagulation testing: do we need a discard tube?
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.
authors.affiliation: Clinical Haematology, Haemato-Oncology and Bone Marrow (Stem Cell) Transplant Unit, Christian Medical College & Hospital, Ludhiana, Punjab India.
authors.forename: Markas
authors.initials: M
authors.lastname: Masih
authors.affiliation: Department of Pathology, Christian Medical College & Hospital, Brown Road, Ludhiana, 141 008 Punjab India.
authors.forename: Naveen
authors.initials: N
authors.lastname: Kakkar
keywords: Activated partial thromboplastin time; Coagulation; Discard tube; Prothrombin time