If you obtain a platelet count from a blood sample collected in a sodium citrate tube, the result is multiplied by 1.1 to correct for the volumetric difference in anticoagulant compared with EDTA. When you result the platelet count from the sodium citrate tube, is it a CAP requirement to attach a comment such as: “_#__ Results reported from blue top tube. The reference range and other method performance specifications have not been established or approved by FDA. Use results with caution.”
The anticoagulant of choice when testing on a
hematology analyzer is EDTA (purple top). Unfortunately, EDTA can also
cause in vitro platelet clumping in certain individuals. When this
occurs the standard practice is to collect a specimen with sodium
citrate (blue top) as the anticoagulant. The blue top specimen must be
filled fully to maintain the appropriate blood-to-coagulant ratio. The
platelet results are then multiplied by 1.1 to obtain the final result.
It is not required to add a disclaimer since this is a mechanism to
correct a problem with the specimen and the original anticoagulant.
The CAP checklist requirement follows in its entirety, including references.
There
is an adequate system (such as microscopic correlation with the blood
film) to prevent reporting of spurious thrombocytopenia when platelet
clumps, giant platelets, or platelet satellitism are present.
NOTE:
When platelet satellitosis (satellitism), significant numbers of giant
platelets and/or platelet clumps are suspected/detected by
cyto/histographic abnormalities or instrument rejection of a platelet
result, the platelet concentration must be independently verified.
Correlation with a well-prepared blood film must be made. If platelets
are clumped after collection in an EDTA-anticoagulated tube that was
well-mixed at the time of collection, this may represent in vitro
EDTA-induced changes; platelets should be quantified from blood
collected directly into a counting diluent, or by use of a different
anticoagulant (e.g. liquid sodium citrate with subsequent adjustment for
dilution) or by estimation from a non-anticoagulated blood film.
Evidence of Compliance:
- Written procedure defining the methods used to detect spurious thrombocytopenia or platelet abnormalities and to correct results AND
- Record showing actions taken to verify platelet concentration prior to reporting.
References: http://captodayonline.com/qa-column-0816/
- Hyun BH, et al. Platelet satellitosis. Chicago, IL: American Society of Clinical Pathology Check Sample H-78, 1976.
- Veenhoven WA, et al. Pseudothrombocytopenia due to agglutinins. Am J Clin Pathol. 1979;72:1005-1008.
- Gloster ES, et al. Spurious platelet counts associated with bacteremia. Am J Hematol. 1985;18:329-332.
- Cunningham VL, Brandt JT. Spurious thrombocytopenia due to EDTA-independent cold-reactive agglutinins. Am J Clin Pathol. 1992;97:359-362.
- Hanseler E, et al. Estimation of the lower limits of manual and automated platelet counting. Am J Clin Pathol. 1996;105:782-787.
- Bridgen ML, Dalal BU. Cell counter-related abnormalities. Lab Med. 1999;30:325-334.
- Kunicka JE, et al. Improved platelet counting using two-dimensional laser light scatter. Am J Clin Pathol. 2000;114:283-289.
