Serum or plasma sample – which one is better? Presented by: Jeffrey Chance, PhD 04/2011 Presentation Overview • • • • • • • • Introduction Turnaround Time Sample Quality H dli & T Handling Temperature Eff Effects Test Results / Analyte Stability Advantages & Disadvantages Which Sample is Better ? Summary 2 What Type of Plasma ? • Lithium heparin is the preferred anticoagulant in clinical c ca cchemistry. e st y • EDTA, citrate and oxalate cannot be used for routine chemistry testing since they bind calcium and have commonly measured counterions (K, Na). • The lithium salt is more commonly used than the sodium salt to avoid interference with sodium determinations. determinations 3 Which Sample is Better ? 1 Serum 1. 2. Heparin p Plasma 3. It Depends / Equal 4 Turnaround Time • Recommended clotting times for serum blood collection co ect o tubes ge generally e a y range a ge from o 30 30-60 60 minutes. utes • Use of plasma allows laboratories to process and test specimens upon receipt receipt, while avoiding latent fibrin formation due to incomplete clotting. • Plasma advantage where specimen must be centrifuged without delay, eg. ER/STAT, end of day courier pickup pickup. 5 Time from phlebotomy t to centrifugation > 30 min Yes Serum or Plasma No Are serum specimens held to ensure minimum clot time? Yes Use of plasma can improve TAT No Use of plasma can reduce fibrin 6 Sample Quality • Serum specimens are subject to latent fibrin formation o at o when e cclotting ott g is s inadequate. adequate - insufficient clotting time - patients receiving anticoagulant or thrombolytic therapy • Fibrin can range from thin strands to large cloud-like masses. 7 Issues Due To Fibrin • Physical obstruction of sampling probe • Insufficient sampled volume • Gradual deposition of fibrin in reaction chambers or pathways • Interference with measurement systems or reagents • Potential consequences: instrument downtime, failure to provide test results, or erroneous test results. 8 Addressing Fibrin Issues • Approaches to minimize the impact of fibrin in serum specimens spec e so often te require equ e use user intervention, te e t o , increase c ease TAT, and may not be recommended. • To help reduce these issues issues, some laboratories have switched to plasma. • However, However plasma specimens also have unique characteristics concerning specimen quality and integrity. integrity 9 Sample Quality • Serum almost “cell free”. • Separation of anticoagulated blood based on density gradient: platelets (least dense) > white blood cells > red blood cells (most dense) • Platelets most abundant in plasma followed by WBC. 10 Sample Quality • "Clean" plasma (low cell/platelet counts) can be obtained obta ed with t p proper ope ce centrifugation. t ugat o • Non-gel tubes – cells/platelets near bulk cell interface Plasma often aliquoted interface. aliquoted. • Gel tubes – rapid gel movement traps cells/platelets before sedimentation is complete complete. Some cells/platelets above gel surface. Plasma not aliquoted. aliquoted 11 serum plasma 12 Gel Movement • The presence of a solid clot in serum gel tubes leads to a d difference e e ce in tthe e movement o e e to of ge gel du during g centrifugation. • Serum: Gel must move up and around the clot clot, against the tube wall. • Plasma: Gel moves up in pieces similar to a ‘lava lava lamp’. 13 Gel Movement (simulated) serum tube plasma tube 14 Test Results • In general, most assays in clinical chemistry are compatible co pat b e with t bot both serum se u a and d heparin epa p plasma, as a, a and d test results are sufficiently equivalent that the same reference ranges g can be used. • However, for certain assays or test methods, plasma specimens may be unacceptable unacceptable, or differences in results may be sufficient to warrant a change in reference range range. 15 Potassium • Potassium and phosphorus increased in serum due to release e ease from o ce cells/platelets s/p ate ets du during g cclotting. ott g • A linear correlation has been shown between platelet count and the increase in serum potassium potassium. World Health Organization. Use of anticoagulants in diagnostic laboratory investigations. WHO/DIL/LAB/99.1 Rev.2, 2002. Harr R, Bond L, Trumbull D. A comparison of results for serum versus heparinized plasma for 30 common analytes. Lab Med. 1987;18:449-55. Ciuti R, Rinaldi G. Serum and plasma compared for use in 19 common chemical tests performed in the Hitachi 737 analyzer. Clin Chem. 1989;35:1562-3. Guder WG, Narayanan S, Wisser H, Zawta B. Samples: from the patient to the laboratory. 3rd ed. Darmstadt, Germany: Wiley-VCH; 2003:32-3. Miles RR, Roberts RF, Putnam AR, Roberts WL. Comparison of serum and heparinized plasma samples for measurement of chemistry analytes. Clin Chem. 2004;50:1704-5. B ti CA, Burtis CA A Ashwood h d ER ER, eds. d Tietz Ti t fundamentals f d t l off clinical li i l chemistry. h i t 4th ed. d Phil Philadelphia, d l hi PA PA: W W.B. B S Saunders d C Company; 1996 1996:499. 499 Hartland AJ, Neary RH. Serum potassium is unreliable as an estimate of in vivo plasma potassium. Clin Chem. 1999;45:1091-2. 16 Potassium • Patients with essential thrombocythaemia and significant s g ca t tthrombocytosis o bocytos s were e e found ou d to have a e se serum u pseudohyperkalemia (> 5.5 mmol/L) that corrected when measured on plasma. p • It has been suggested that when there is no obvious explanation for an elevated serum potassium potassium, the plasma potassium level should be measured, particularly in patients with elevated platelet counts counts. Howard MR, Ashwell S, Bond LR, Holbrook I. Artefactual serum hyperkalaemia and hypercalcaemia in essential thrombocythaemia. J Clin Pathol. 2000;53:105-9. Fort JA. Thrombocytosis and hyperkalemia revisited. Am J Pediatr Hematol Oncol. 1989;11:334-6. 17 Total Protein • Slightly increased in plasma due to presence of fibrinogen. b oge World Health Organization. Use of anticoagulants in diagnostic laboratory investigations. WHO/DIL/LAB/99.1 Rev.2, 2002. Harr R, Bond L, Trumbull D. A comparison of results for serum versus heparinized plasma for 30 common analytes. Lab Med. 1987;18:449-55. Ciuti R, Rinaldi G. Serum and plasma compared for use in 19 common chemical tests performed in the Hitachi 737 analyzer. Clin Chem. 1989 35 1562 3 1989;35:1562-3. Guder WG, Narayanan S, Wisser H, Zawta B. Samples: from the patient to the laboratory. 3rd ed. Darmstadt, Germany: Wiley-VCH; 2003:32-3. 18 Other Tests • Differences in certain enzymes (e.g., LD, ALKP, AST) may ay be see seen. • Lithium/sodium increased with use of lithium or sodium heparin heparin. • Interference from fibrinogen may also make plasma an unsuitable specimen for certain protein analysis methods (e.g., protein electrophoresis). • Heparin H i may iinterfere t f with ith certain t i iimmunoassays. Lee DC L DC, Kl Klachko hk MN MN. F Falsely l l elevated l t d lithi lithium llevels l iin plasma l samples l obtained bt i d iin lithi lithium containing t i i ttubes. b JT Toxicol i l Cli Clin T Toxicol. i l 1996;34:467-9. 19 Handling Effects • Mixing/agitating plasma gel tubes after centrifugation will re-suspend e suspe d ce cells sa and dp platelets ate ets • Specimen may appear slightly darker or cloudy 20 unmixed mixed 21 Temperature Effects • Temperature can also influence plasma sample qua ty quality. • Cold activation of clotting factors • Refrigeration may drive reaction towards clotting --> > increase in fibrin and cell aggregate formation • Re-centrifugation R t if ti off stored t d plasma l aliquots li t can h help l clean up sample prior to testing. 22 Analyte Stability • Heparin plasma samples with increased cell/platelet concentrations co ce t at o s e exhibit b t reduced educed stab stability ty o of ce certain ta common analytes. • Analytes affected are involved in cell/plateletmediated metabolic processes and/or are present in higher concentration in cells or platelets platelets. 23 Analyte Stability • Heparin plasma stability data for routine chemistry analytes, a a ytes, 24 hours ou s at room oo te temperature: pe atu e - Aliquot from non-gel tube: STABLE - Plasma stored in gel tube: decreases in glucose and CO2; increases in phosphorus, K, LD • Plasma Pl stored t d in i contact t t with ith cells ll – significant i ifi t changes in glucose and other analytes over time† BD White Paper VS7172. Comparison of BD Vacutainer® PST™ II Plus Tubes With BD Vacutainer® Lithium Heparin Glass Tubes for Routine Chemistry Analytes. 2004. BD White Paper VS7174. Comparison of BD Vacutainer® Lithium Heparin Plus Tubes With BD Vacutainer® Lithium Heparin Glass Tubes for Routine Chemistry Analytes. 2004. †B Boyanton t BL JJr, Bli Blick k KE KE. Stability St bilit studies t di off ttwenty-four t f analytes l t in i h human plasma l and d serum. Cli Clin Ch Chem. 2002 2002;48:2242-7. 48 2242 7 24 Analyte Stability • Some mechanisms are temperature dependant – e.g., e g , low o te temperature pe atu e may ay cause higher g e increase c ease in K due to inhibition of Na+,K+-ATPase activity. • Laboratories should evaluate the need for delayed or add-on testing when considering the use of heparin plasma samples samples. Guder WG, Narayanan S, Wisser H, Zawta B. Samples: from the patient to the laboratory. 3rd ed. Darmstadt, Germany: Wiley-VCH; 2003:57. Heins M, Heil W, Withold, W. Storage of serum or whole blood samples? Effects of time and temperature on 22 serum analytes. Eur J Clin Chem Clin Biochem. 1995;33:231-8. 25 Analyte Stability • Remember that courier pick-up? (plasma (p as a ad advantage a tage for o immediate ed ate ce centrifugation) t ugat o ) • Was the plasma aliquoted or in a gel tube? • What tests were ordered? • What is the transit time/delay until testing? 26 Ad Advantages t Serum – nearly cell-free – good storage stability for most analytes – wide range of assays available Pl Plasma – shorter h t TAT: TAT can be b centrifuged t if d immediately i di t l – faster gel movement in gel tubes/ more reproducible gel barrier formation – more representative of in vivo state – available plasma yield slightly higher than serum 27 Di d Disadvantages t Serum – may cause pseudohyperkalemia – longer TAT – instrument or test interference from fibrin, esp. with anticoagulation therapy Pl Plasma – higher hi h cell/platelet ll/ l t l t counts; t potential t ti l ffor instrument i t t or test t t interference – reduced storage stability for certain analytes; fibrin f formation i during d i storage – interference from anticoagulant – interference from fibrinogen g – some tests may not be supported 28 Serum vs. Plasma • Serum usage generally still predominant but varies by region. eg o • Many laboratories try to standardize to one sample type and will rely heavily on that one type type. • A main reason for not using plasma samples in laboratories currently is because laboratory processes are standardized for serum samples. • The Th main i driver di ffor using i plasma l samples l iis th the shortened TAT. 29 Serum vs. Plasma • Top Serum Advantages / Plasma Disadvantages: Assay ssay co compatibility pat b ty • Top Plasma Advantages / Serum Disadvantages: Turnaround time, fibrin, (hemolysis) 30 Which Sample is Better ? • How much weight does each factor carry in your institution st tut o or o sett setting? g 31 Which Sample is Better ? Fibrin TAT Stability Assay Compatibility 32 Which Sample is Better ? Fibrin TAT Stability Assay Compatibility 33 Which Sample is Better ? Fibrin TAT Stability y Assay Compatibility 34 Summary • Serum and heparin plasma both have benefits and limitations tat o s in clinical c ca chemistry. c e st y • The selection of serum vs. heparin plasma may be dependent on the specific setting/population. setting/population • Standardizing on one sample type may be desirable but not always practical practical. 35 Thank You 36
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