Platelet Count

CPT: 85049
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  • Platelets
  • Thrombocyte Count

Expected Turnaround Time

Within 1 day

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Specimen Requirements


Whole blood. Peripheral blood smears prepared at the time of collection may also be useful, particularly when platelet aggregation is a problem.


Tube fill capacity

Minimum Volume

0.5 mL (500 μL for pediatric microtainer capillary tubes; fill tube to capacity.) (Note: This volume does not allow for repeat testing.)


Lavender-top (EDTA) tube.


Invert tube immediately 8 to 10 times once tube is filled at time of collection.

Storage Instructions

Maintain specimen at room temperature.

Stability Requirements



Room temperature

1 day


3 days



Freeze/thaw cycles


Causes for Rejection

Hemolysis; clotted specimen; tube not filled with minimum volume; improper labeling; transfer tubes with whole blood; specimen diluted or contaminated with IV fluid; specimen received with plasma removed; specimen collected in any anticoagulant other than EDTA

Test Details


Evaluate, diagnose, and/or follow up bleeding disorders, drug-induced thrombocytopenia, idiopathic thrombocytopenia purpura (acute or chronic), disseminated intravascular coagulation, leukemia states, chemotherapeutic management of malignant disease states; investigate purpura, petechiae; evaluate response to platelet transfusions, steroids, or other therapy


Clumping may cause false low count.1 Platelet satellitism around neutrophils will cause a pseudothrombocytopenia. RBC or WBC fragments including fragmented fragile leukemic cells and neutrophil pseudoplatelets2 may cause falsely elevated counts.


Automated cell counter; microscopic exam of peripheral smear if specific criteria are met

Additional Information

The platelet, of growing practical clinical importance in hemostatic considerations and a variety of medical/surgical processes is also fundamental to etiologic considerations of arteriosclerotic3 and malignant disease.4

Careful estimate of platelet number from stained peripheral blood smear can provide useful information. A variety of factors affect the distribution of platelets on a peripheral blood smear, and thus platelet estimates lack precision. Capillary blood platelet counts (c.f. to venous blood counts) may be significantly underestimated. Platelets are often clumped on smears obtained from capillary blood, contributing to imprecision. A small whole blood clot or very small fibrin clots in the EDTA anticoagulated specimen will usually be associated with clumping of platelets on the slide, and with a false low platelet count.

Quantitative platelet disorders have varied etiology. Thrombocytopenia may have an immunologic basis, the result of production deficiency due to the effect of drugs or physical agents, abnormal platelet pooling or increased destruction (eg, sequestration by large vascular tumor), or result from a variety of probably nonimmunologic mechanisms (eg, hypersplenism). Decreases may occur after bleeding, transfusion, infections, or relating to defective production of or regulation by thrombopoietin.

Drugs and chemicals associated with thrombocytopenia, often on an immune mediated basis5 or as the result of marrow suppression, include quinidine, quinine, heparin, gold salts, sulfas, rifampicin, ASA, digitoxin, apronal, chlorothiazides, chlorpropamide, meprobamate, antihistamines, chloramphenicol, penicillin, DDT, benzol, a variety of other industrial organic chemicals, diphenylhydantoin, PAS, hydrochlorothiazide, phenylbutazone, and a variety of antineoplastic chemotherapeutic agents. ASA acts by acetylating cyclo-oxygenase.

Thrombocytosis is less common, but likewise varied in etiology: physiologic (eg, postpartum, or after exercise); myeloproliferative syndromes (eg, thrombocythemia, some cases of chronic myelogenous leukemia, myelofibrosis with myeloid metaplasia); rebound following thrombocytopenia, marrow regenerative activity after bleeding episode, hemophilia, iron deficiency; asplenism, infections, inflammatory or malignant disease, especially carcinomatosis. Oral contraceptives may cause slight increase.

Congenital causes of thrombocytopenia include Wiskott-Aldrich syndrome, May-Hegglin anomaly, thrombocytopenia with absent radius, and Bernard-Soulier syndrome. See table.

Inherited Abnormalities of Platelet Production (Characterized by Thrombocytopenia)





Adapted from Penner J. Blood Coagulation Laboratory Manual. University of Michigan Medical School; Sep, 1979.


Autosomal Dominant

Severe thrombocytopenia

Platelet replacement



Severe thrombocytopenia with small platelets

Possibly splenectomy

Congenital thrombopoietin deficiency

? Autorecessive

Severe thrombocytopenia

Plasma transfusion

Thrombocytopenia with absent radius


Moderate thrombocytopenia

Platelet replacement

Abnormalities of Platelet Function, Familial Transmission, Autorecessive


Absent clot retraction, absent aggregation, mild thrombocytopenia

Platelet replacement, steroids

Bernard-Soulier syndrome

Giant platelets, absent Ristocetin® aggregation

Platelet replacement

Platelet storage pool disease

Absent aggregation with collagen, mild thrombocytopenia, absent dense granules with decreased platelet serotonin

Splenectomy, platelet replacement

Hermansky-Pudlak syndrome

Aggregation abnormal with epinephrine and collagen, decreased dense granules and absent ADP stores

Platelet replacement

Release reaction abnormalities

Absent second wave aggregation with epinephrine and collagen, absent PF-3 release, varied inheritance

Platelet replacement


1. Solanki DL, Blackburn BC. Spurious leukocytosis and thrombocytopenia. A dual phenomenon caused by clumping of platelets in vitro. JAMA. 1983 Nov 11; 250(18):2514-2515. 6632146
2. Merz B. Newly identified particle may explain spurious platelet count. JAMA. 1983 Jun 17; 249(23):3146-3147. 6854834
3. Halushka PV, Knapp DR, Grimm L. Prostaglandins, thromboxanes, and platelet function. Curr Top Hematol.1979; 2:75-143.
4. Doolittle RF, Hunkapiller MW, Hood LE, et al. Simian sarcoma virus onc gene, v-sis, is derived from the gene (or genes) encoding a platelet-derived growth factor. Science. 1983 Jul 15, 221(4607):275-277. 6304883
5. Moss RA. Drug-induced immune thrombocytopenia. Am J Hematol. 1980; 9(4):439-446.6452056


Rajasekhar A, Gernsheimer T, Stasi R, James AH.2013 Clinical Practice Guide on Thrombocytopenia in Pregnancy. Available at: Washington, DC: American Society of Hematology; 2013. Accessed June 30, 2014.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
005249 Platelet Count 777-3 015172 Platelets x10E3/uL 777-3

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