Three STAT Specimens, One Wrong Spin, and a Hematocrit of 58%
At 5:40 a.m., three STAT specimens from one ED patient arrive in the core lab by pneumatic tube: a light-blue 3.2% sodium citrate tube for PT/INR, a lithium heparin green top for ammonia and potassium, and a gold serum separator tube for troponin. The tube-system log shows a 4:55 a.m. draw time. The same draw's CBC reports a hematocrit of 58%. The green top is still uncentrifuged and has sat at room temperature since arrival; the technologist on duty plans to spin it with the rest of the run at 3,000 rpm for 10 minutes, then load all three. A note on the requisition reads "rule out hepatic encephalopathy." The ED calls at 5:45 for the ammonia.
1. What is wrong with the handling of the green-top tube, and what do you do with the ammonia and potassium results?
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The problem: ammonia is generated in vitro. Every minute the plasma sits on cells at room temperature, red cells and platelets release ammonia, so the value climbs steadily and can be spuriously doubled or more by 45–60 minutes of contact. The tube was not placed on ice, was not separated promptly, and is now roughly 45 minutes old and unspun. 'Heparin tubes don't need ice' is exactly the misconception that generates a false hyperammonemia workup.
Action on ammonia: do not report it. Recollect with proper technique - on ice, centrifuged cold, plasma separated within the validated window (commonly 15 minutes), and analyzed promptly - and tell the ED explicitly that the first result is being cancelled for specimen-handling reasons so the team does not treat a number that does not exist.
Action on potassium: the same delay allows potassium to leak from cells, so a green-top potassium from this tube is potentially falsely elevated. Check the hemolysis index; if potassium is elevated or critical, recollect before reporting as critical. The troponin in the gel tube is comparatively forgiving of a short delay, but the tube should still be separated within the validated time.
2. The PT/INR was drawn into a standard 1:9 citrate tube from a patient whose hematocrit is 58%. What is the expected effect, and what are your options?
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Effect: the citrate volume in the tube is fixed while the plasma fraction is not. At a hematocrit of 58%, there is markedly less plasma per unit of whole blood, so the citrate is present in relative excess. Extra citrate chelates additional calcium, the recalcitration step is underpowered, and clotting times are falsely prolonged - the INR reads higher than the patient's true value. Acting on that number risks unnecessary plasma or vitamin K, or an inappropriate hold on anticoagulation.
Options, in order of preference:
- Recollect into a citrate tube with a reduced citrate volume calculated for the patient's hematocrit (the standard approach is the CLSI formula: citrate volume = (100 − Hct)/595 × blood volume), filled to the tube's draw line. Many labs keep premeasured tubes or a documented procedure for this.
- If immediate recollection is impossible and the result is needed urgently, report it only with an explicit comment that the specimen came from a patient with Hct >55% and the result may be falsely prolonged, and notify the provider directly.
Either way, document the hematocrit on the requisition and flag the patient's record so future citrate draws are adjusted prospectively rather than caught after the fact.
3. The EDTA specimen from the same draw is a full, well-mixed 4 mL lavender tube. Would you expect any hematology issue from that specimen, and would it change your handling of the other tubes?
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The EDTA tube itself is not the problem - a full, adequately mixed lavender tube is valid at a hematocrit of 58%; grossly elevated hematocrit mainly matters for anticoagulant ratio in citrate tubes and, at extreme values, for the EDTA tube's own anticoagulant-to-blood ratio.
The important implication is procedural: the 58% hematocrit is the piece of information that reframes the PT/INR as unreliable. That means the CBC result is not just a separate reportable - it is an interpretive key for another specimen in the rack. A technologist working tube-by-tube would report a prolonged INR and never connect it to the hematocrit sitting in the same run. The practical habit is to review the full specimen set from one draw before releasing any of it, and to treat a very high or very low hematocrit as a flag for every citrate tube drawn on that patient.