The complete blood count, or CBC, is utilized in monitoring various disease processes including, but not limited to, bacterial and viral infections, anemias, leukemias, vitamin deficiencies, clotting disorders and congenital abnormalities.1
Although these tests are often highly automated and performed frequently, laboratory professionals are armed with the knowledge to analyze and interpret quality of the results due to the many analytical issues that can affect those results.1 Pseudothrombocytopenia produced by Ethylenediaminetetraacetic Acid (EDTA) platelet sensitivity, clotted samples, lipemia, cold agglutinins and dilutional effects (contamination with IV fluids, etc.) can all lead to erroneous CBC results.
EDTA-induced Pseudothrombocytopenia is not fully understood but may involve platelet autoantibodies.2 It is important if this is suspected to investigate it further to prevent treatment based on an erroneous platelet result.2 Scanning the peripheral blood smear to include the outer edges for platelet clumps is the first step in the investigation.2
If platelet clumps are noted, try vortexing the sample for about 60 seconds, analyze it and make a slide to see if the clumps are dispersed.2 If so, the platelet count is probably accurate. If this does not correct the problem, the sample should be recollected in a sodium citrate tube and analyzed correcting the platelet count for the appropriate dilution factor.2 It is a good idea to evaluate the platelets on the peripheral smear from the sodium citrate tube as well.2
Every laboratory technician or technologist knows you cannot analyze a CBC on a clotted sample. Clots that are macrosopic or microscopic in nature can affect the parameters of the CBC.3 Parameters affected include white blood cell count, red blood cell count, platelet count and red cell indices.3,4
With clotted samples and EDTA platelet sensitivity, clumping can cause cellular interference in the analysis of the CBC.5 If a sample is suspected of containing microscopic or macroscopic clots, the sample should be recollected and analyzed.
Lipemia has been known to affect CBC results as well. Hemoglobin is particularly affected.5,6 Several options are available in dealing with lipemic samples:
- "Report only the hematocrit, RBC, MCV, WBC and platelet count and indicate an accurate Hb is not available due to lipemia, and suggest repeating the tests after the patient has fasted at least two to three hours."
- (Requires additional instrumentation): "determine a whole blood Hb (Hemocue) that is not affected by lipemia due to multiple wavelengths used in the determination. The full CBC battery can then be reported by combining the whole blood Hb with the valid analyzer determinations and calculating the missing indices."
- Saline replacement procedure: Spin down the sample (or an aliquot of the original sample) and remove the lipemic plasma trying not to disturb the buffy coat, or are just above it, containing the platelets. Replace the plasma with saline, mix well and analyze.6
Cold agglutinins are yet another contributor of erroneous CBC results. Cold agglutinins decrease red blood cell counts, increase mean cell volume (MCV), mean cell hemoglobin (MCH) and mean cell hemoglobin concentration (MCHC).7 Typically, the H&H will not match.
When I suspect a sample of containing cold agglutinins, I will pre-warm the sample in a heat block for approximately 10 minutes and then analyze again. If that is not successful, I will try increasing the incubation time; and, if still unsuccessful, I will perform a saline replacement procedure (see above); however, I use pre-warmed saline instead of room-temperature saline in the replacement. I then warm the sample for approximately ten minutes and analyze.
Last, but not least, I will discuss dilution effects. CBC results, particularly the hematocrit are susceptible to dilution, so any sample suspected to being contaminated with IV fluids should be recollected.8
This was certainly not an all-inclusive list of the many factors that can contribute to erroneous CBC results. These are the most frequent ones that I encounter and wanted to summarize briefly here. As laboratory professionals we must always work diligently to make sure we are reporting results that are of the utmost quality.
Regina Owens is clinical laboratory scientist, Healthmark Regional Medical Center, Defuniak Springs, FL.
1. FDA. Executive summary: Overview of the FDA waiver process. Available at: www.fda.gov/OHRMS/DOCKETS/ac/08/briefing/2008-4375b1-01.pdf. Last accessed July 28, 2009.
2. Owens R. Pseudothrombocytopenia. Available at: http://laboratorian.advanceweb.com/editorial/content/editorial.aspx?cc=74464. Last accessed July 28, 2009.
3. Bio-Reference Laboratories Inc. Specimen quality. Available at: www.bioreference.com/specqual.htm. Last accessed July 28, 2009.
4. Pathology Department, Good Hope Hospital. Haematology. Available at: www.goodhope.org.uk/departments/pathweb/HAE_home.htm. Last accessed July 28, 2009.
5. Aulesa C, Pastor I, Naranjo D, et al. Validation of the Coulter LH 750 in a hospital reference laboratory. Available at: http://static.cjp.com/gems/labdev/restrict/LH.9.1.15.pdf. Last accessed July 28, 2009.
6. CAP Today. Q&A. Available at: www.cap.org/apps/portlets/contentViewer/show.do?printFriendly=true&contentReference=cap_today%2Fq_and_a%2Fqa_07_0 4.html Last accessed July 28, 2009.
7. Breuer GS, Raveh D, Rudensky B. Remember the blood smear: A clinical laboratory vignette. Available at: www.ima.org.il/imaj/ar02nova-31.pdf. Last accessed July 28, 2009.
8. RightHealth.com. Hematocrit. Available at: www.answers.com/topic/hematocrit. Last accessed July 28, 2009.