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RETICULATED PLATELETS
Reticulated Platelets are young platelets that contain residual mRNA and rRNA when they are
released from the bone marrow into the peripheral circulation as a result of thrombopoiesis. These
are often called "large, young" platelets or "stress" platelets and appear normally in the peripheral
blood at low levels (up to 4.5% of total platelets). The correlation with size is generally proportional
as large platelets often contain more RNA. However, platelets of all sizes can be found with
increased RNA content which indicates that correlation with the Mean Platelet Volume (MPV) is
subject to variability and that MPV alone cannot be used to enumerate all young platelets.
By analogy to reticulated erythrocytes (reticulocytes), an increased proportion of reticulated platelets
in blood indicates increased thrombopoiesis and is therefore a reflection of megakaryocyte number and
activity. Thus, it is frequently possible to distinguish decreased production or bone marrow
failure from increased platelet consumption as the cause of thrombocytopenia using only a
peripheral blood sample. In some cases this may preclude the need to perform a bone marrow
examination for a megakaryocyte count, and avoid discomfort or hemorrhagic risk in
thrombocytopenic patients. The percentage of reticulated platelets and platelet count may also be
used to calculate an absolute reticulated platelet count for early marrow transplantation monitoring.
Quantitation of reticulated platelets is achieved by combining a monoclonal antibody specific for
platelets and an RNA-specific vital dye (thiazole orange) with analysis by flow cytometry, allowing
the rapid and accurate cytometric quantitation of hundreds of events. Platelets are specifically
identified for the direct determination of RNA content regardless of size and concentration.
Applications include: 1) thrombocytopenia work-ups, 2) monitoring course and treatment of
Idiopathic Thrombocytopenic Purpura (ITP), 3) bone marrow transplantation success, 4) monitor
chemotherapy and other marrow suppressives, 5) ITP of pregnancy and pre-eclamptic states, 6) effects
on thrombopoiesis of megakaryocyte growth factors, 7) assess platelet donors and donated products.
Sample Requirements:
A 7 or 10 mL EDTA-anticoagulated (lavender top) whole blood sample is stable for 48 hours. A
10 mL ACD-A anticoagulated (yellow top) whole blood is stable up to 72 hours and
recommended for overnight shipping. Ship at ambient temperature. Report includes the
reticulated platelet count and correlation with platelet morphology by our staff pathologist.
Routine turnaround time (TAT) is 48 hours, 8 hours if "STAT." (Note: Allow at least one week
before performing a reticulated platelet assessment in patients who have received a platelet transfusion.)
References:
1) Kienast J, and G Schmitz. Flow cytometric analysis of thiazole orange uptake by platelets: a diagnostic aid in the evaluation of thrombocytopenic disorders. Blood 75: 116-121, 1990.
2) Ault, KA, HM Rinder, J Mitchell, MB Carmody, CP Vary, and RS Hillman. The significance of platelets with increased RNA content (reticulated platelets). A measure of the rate of thrombopoiesis. Am J Clin Pathol 98: 637-646, 1992.
3) Ault, KA. Flow cytometric measurement of platelet function and reticulated platelets. Ann N.Y.Acad Sci 677: 293-308,1993.
4) Rinder,HM, et.al. Reticulated platelets in the evaluation of thrombopoietic disorders. Arch Pathol Lab Med 117: 606-610, 1993.
5) Richards E and Baglin P. Quantitation of reticulated platelets: methodology and clinical application. Br J Hem 91: 445-51, 1995.
6) Ogata H. Measurement of reticulated platelets in thrombocytopenia. Kurume Med J 45: 165-170, 1998. V. 11/02