Hi, Sutirtha. Remember that the “empty” red top tubes actually have clot activator (required to make blood clot in plastic tubes). If there is insufficient clot activator in the tube lots you have or, more likely, there is insufficient mixing immediately after collection, the centrifugation may be taking place before clotting is complete. Thus, clotting of the supernatant plasma may be occurring in the absence of the already pelleted cells. Recall that it often takes 15-20 minutes for blood to clot well in tubes (longer if the patient is on anticoagulants). I agree with Michael Peake – there are a lot of advantages to using Li heparin plasma for neonates. Rarely do you need serum. Hope to see you in Atlanta. -Jim From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Dr. Sutirtha Chakraborty Sent: Tuesday, June 16, 2015 2:22 AM To: [log in to unmask] Subject: Problems with BD Microtainer Red Top Tubes Dear Mailbase, We are facing a weird problem with our Pediatric samples. The serum is clotted in most samples drawn. This problem started with the use of the BD Microtainer red top collection tubes. Attached is a photograph. We also used a different Lot of tubes from the same manufacturer, but still the problem remains Anyone with similar experiences? -- Dr Sutirtha Chakraborty, MBBS, MD, FACB Chief Consultant, Department of Biochemistry Peerless Hospital & B.K Roy Research Center Kolkata 700094, West Bengal, India Mobile: +91 9874787638 ------ACB discussion List Information-------- This is an open discussion list for the academic and clinical community working in clinical biochemistry. Please note, archived messages are public and can be viewed via the internet. Views expressed are those of the individual and they are responsible for all message content. ACB Web Site http://www.acb.org.uk<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.acb.org.uk&d=AwMFaQ&c=SgMrq23dbjbGX6e0ZsSHgEZX6A4IAf1SO3AJ2bNrHlk&r=_4rCeX3TSQgrdhhwEl4yDs13b8mZhuDoiRSP4oKKuU4&m=s5j4oh4Yr2LeW0AbwIxjBKbVEu86Vq-4hrZV_MnIcOo&s=wetq_aAT09BECX-1Jfjy44N6NXZ_HdHw0xHEuQ0Ib8k&e=> Green Laboratories Work http://www.laboratorymedicine.nhs.uk<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.laboratorymedicine.nhs.uk&d=AwMFaQ&c=SgMrq23dbjbGX6e0ZsSHgEZX6A4IAf1SO3AJ2bNrHlk&r=_4rCeX3TSQgrdhhwEl4yDs13b8mZhuDoiRSP4oKKuU4&m=s5j4oh4Yr2LeW0AbwIxjBKbVEu86Vq-4hrZV_MnIcOo&s=VQWABpx1MGhFrIBYVHHhYWLVu9E8K_8WqFVvMBS4wgo&e=> List Archives http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.jiscmail.ac.uk_lists_ACB-2DCLIN-2DCHEM-2DGEN.html&d=AwMFaQ&c=SgMrq23dbjbGX6e0ZsSHgEZX6A4IAf1SO3AJ2bNrHlk&r=_4rCeX3TSQgrdhhwEl4yDs13b8mZhuDoiRSP4oKKuU4&m=s5j4oh4Yr2LeW0AbwIxjBKbVEu86Vq-4hrZV_MnIcOo&s=1Iqm-D5v4haVQflSLpgVw-M3IZe6V32k8bcQLH0yimo&e=> List Instructions (How to leave etc.) http://www.jiscmail.ac.uk/<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.jiscmail.ac.uk_&d=AwMFaQ&c=SgMrq23dbjbGX6e0ZsSHgEZX6A4IAf1SO3AJ2bNrHlk&r=_4rCeX3TSQgrdhhwEl4yDs13b8mZhuDoiRSP4oKKuU4&m=s5j4oh4Yr2LeW0AbwIxjBKbVEu86Vq-4hrZV_MnIcOo&s=HgS1Qkw1xFg6VtgZFnhNFmydipAC8ua1mqq1nPDCHJc&e=> ------ACB discussion List Information-------- This is an open discussion list for the academic and clinical community working in clinical biochemistry. Please note, archived messages are public and can be viewed via the internet. Views expressed are those of the individual and they are responsible for all message content. ACB Web Site http://www.acb.org.uk Green Laboratories Work http://www.laboratorymedicine.nhs.uk List Archives http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html List Instructions (How to leave etc.) http://www.jiscmail.ac.uk/