ARCHIVES
OF
PRACTICAL PEDIATRICS
A News Letter Devoted To Practical Pediatric Practice
Volume 4 Issue 3 Date March 2022
Editor in Chief:
BD Gupta
Ass Editor:
RK Maheshwari
Mohan Makwana
Anil Arora
Regional Editors
Pankaj Agrawal
Avinash Bansal
Anil Jain
PC Khatri
Priyanshu Mathur
Jai Singh Meena
Adarsh Purohit
Editorial advisory Board
Neeraj Gupta
Manoj Jangid
Rakesh Jora
Amarjeet Mehta
Lakhan Poswal
GS Sengar
Pramod Sharma
Anurag Singh
Kuldeep Singh
S Sitaraman
Platelets And Platelet Indices
Dr BD Gupta
MD(Paed)
Dr GL Gupta
MD (Med)
Platelets, also called thrombocytes are a component of blood, whose function is to react to bleeding from blood vessel injury by clumping, thereby initiating a blood clot.Low platelet count may lead to bleeding.Platelet indices (PI) i.e. plateletcrit, mean platelet volume (MPV) and platelet distribution width (PDW) are a group of derived platelet parameters obtained as a part of the automatic complete blood count. Emerging evidence suggests that platelet Indices (PIs) may have diagnostic and prognostic value in certain diseases.10-Jun-2016
Platelets And Platelet Indices
DR BD GUPTA
DR GL GUPTA
Platelets, also called thrombocytes are a component of blood, whose function is to react to bleeding from blood vessel injury by clumping, thereby initiating a blood clot. Platelets have no nucleus; they are fragments of cytoplasm that are derived from the megakaryocytes of the bone marrow, which then enter the circulation. Circulating inactivated platelets are biconvex discoid (lens-shaped) structures, 2–3 µm in greatest diameter. Activated platelets have cell membrane projections covering their surface. Platelets are found only in mammals, whereas in other vertebrates, circulate as intact mononuclear cells. .
On a stained blood smear, platelets appear as dark purple spots, about 20% the diameter of red blood cells. A healthy adult typically has 10 to 20 times more red blood cells than platelets. One major function of platelets is to contribute to hemostasis at the site of interrupted endothelium. They gather at the site and, unless the interruption is physically too large, they plug the hole.
Function
1.Platelets attach to substances outside the interrupted endothelium: adhesion,
2.Platelets change shape, turn on receptors and secrete chemical messengers i.e. activation and then
3.They connect to each other through receptor bridges i.e aggregation.[6]
Formation of this platelet plug (primary hemostasis) is associated with activation of the coagulation cascade, with resultant fibrin deposition and linking (secondary hemostasis). These processes may overlap: the spectrum is from a predominantly platelet plug, or “white clot” to a predominantly fibrin, or “red clot” or the more typical mixture.Further,subsequent retraction and platelet inhibition are added as fourth and fifth steps to the completion of the process.
Platelets also participate in both innate[8] and adaptive[9] intravascular immune responses. The platelet cell membrane has receptors for collagen. Following the rupture of the blood vessel wall, the platelets are exposed and they adhere to the collagen in the surrounding connective tissue.
Clinical Significance
Low platelet concentration is called thrombocytopenia, and is due to
1 decreased production or
- increased destruction.
Table 1.Causes of thrombocytopenia:
| DESTRUCTIVE THROMBOCYTOPENIAS |
| A.Primary Platelet Consumption Syndromes |
| 1. Immune thrombocytopenias
1. Acute and chronic ITP 2. Autoimmune diseases with chronic ITP as a manifestation 1. Cyclic thrombocytopenia 2. Autoimmune lymphoproliferative syndrome and its variants 3. Systemic lupus erythematosus 4. Evans syndrome 5. Antiphospholipid antibody syndrome 6. Neoplasia-associated immune thrombocytopenia 3. Thrombocytopenia associated with HIV 4. Neonatal immune thrombocytopenia 1. Alloimmune 2. Autoimmune (e.g., maternal ITP) 5. Drug-induced immune thrombocytopenia (including heparin-induced thrombocytopenia) 6. Post-transfusion purpura 7. Allergy and anaphylaxis 8. Post-transplant thrombocytopenia 2. Nonimmune thrombocytopenias 1. Thrombocytopenia of infection 1. Bacteremia or fungemia 2. Viral infection 3. Protozoan 2. Thrombotic microangiopathic disorders 1. Hemolytic-uremic syndrome 2. Eclampsia, HELLP syndrome 3. Thrombotic thrombocytopenic purpura 4. Bone marrow transplantation-associated microangiopathy 5. Drug-induced 3. Platelets in contact with foreign material 4. Congenital heart disease 5. Drug-induced via direct platelet effects (ristocetin, protamine) 6. Type 2B VWD or platelet-type VWD |
| B.Combined Platelet and Fibrinogen Consumption Syndromes |
| 1. Disseminated intravascular coagulation
2. Kasabach-Merritt syndrome 3. Virus-associated hemophagocytic syndrome
|
| C.IMPAIRED PLATELET PRODUCTION |
| 1. Hereditary disorders
2. Acquired disorders 1. Aplastic anemia 2. Myelodysplastic syndrome 3. Marrow infiltrative process—neoplasia 4. Osteopetrosis 5. Nutritional deficiency states (iron, folate, vitamin B12, anorexia nervosa) 6. Drug- or radiation-induced thrombocytopenia 7. Neonatal hypoxia or placental insufficiency |
| D.SEQUESTRATION |
| 1. Hypersplenism
2. Hypothermia 3. Burns |
Low platelet count may lead to bleeding. When a platelet count is below 50,000, bleeding is more serious if you’re cut or bruised. If the platelet count falls below 10,000 to 20,000 per microliter, spontaneous bleeding may occur and is considered a life-threatening risk.
Thrombocytosis :
A high platelet count may be is referred as thrombocytosis.
This is usually the result of an existing condition (also called secondary or reactive thrombocytosis), such as:
- Cancer, most commonly lung cancer, gastrointestinal cancer, ovarian cancer, breast cancer, or lymphoma
- Anemia, in particular, iron-deficiency anemia and hemolytic anemia
- Inflammatory conditions such as inflammatory bowel disease (IBD)or rheumatoid arthritis
- Infectious diseases such as tuberculosis
- Splenectomy
- Oral contraceptives
Some conditions may cause a temporary increased platelet count. These may include:
- Recovery from significant blood loss, such as from trauma or major surgery
- After physical activity or exertion
- Recovery from excess alcohol consumption and vitamin B12 and folate deficiency
Thrombocythemia
Rarely, thrombocytosis is caused by a disorder. Primary or essential thrombocythemia, is a rare myeloproliferative disorder in which the bone marrow produces an extremely high number of platelets. Often there are no signs and symptoms and the condition is discovered when testing is done for a health check or for other reasons.
Platelet indices
1.Mean platelet volume (MPV), signifies the average size of platelets in the blood. In healthy subjects it typically ranges between 7.2 and 11.7 fL. MPV of over 13 fL tends to occur in hyper destruction, in which case young platelets become bigger and increase in activity, whereas MPV lower than 8 fL is a sign of platelet hypoproduction.
MPV has been analysed as a potential biomarker of patient’s prognosis, with most studies associating its higher value to worse clinical outcome e.g. pancreatic ductal adenocarcinoma regardless of the normalized level of other well-known prognostic markers and myocardial infarction, where those with higher MPV level seemed to be more often associated with poor clinical outcome. Lower MPV level can be related to low-grade inflammation, such as rheumatoid arthritis.
2.Platelet distribution width (PDW) is a marker of platelet anisocytosis, which describes the size distribution of platelets produced by megakaryocytes and increases upon platelet activation. Normally, it is found to vary between 10 and 18% in healthy individuals. However, it has been observed that PDW change in patients suffering from numerous diseases. It allows for this parameter to be considered as a potential biomarker.
PDW seems to be proportionally related to MPV in healthy individuals, however, under non-physiological conditions, such as, threatened preterm labor, they show significant dissonance – a rise in PDW and decrease in MPV. This disrelation was also observed in patient groups with perforated and non-perforated acute appendicitis and in patients with vaso-occlusive crisis in the course of sickle cell disease due to megakaryocyte hyperplasia.
3.Platelet larger cell ratio (P-LCR), another marker of platelet activity, is a percentage of all platelets with a volume measuring over 12 fL circulating in the bloodstream. It normally ranges between 15 and 35%. In a study, direct relation of P-LCR to PDW and MPV, and its inverse relation to platelet count in patients with thrombocytopenia could be observed. P-LCR seems to be more susceptible to alterations in platelet size in comparison to MPV, despite their correlation.
4.Plateletcrit (PCT) measures total platelet mass as a percentage of volume occupied in the blood. The normal range for PCT is 0.22–0.24%. It seems to play an effective screening role in detecting platelet quantitative abnormalities. The PCT is nonlinearly correlated to the platelet count and indicates comparable clinical implication.
Platelet indices are currently under thorough investigation to be applied as potential novel biomarkers in terms of diagnostics and prognosis in various, both acute and chronic diseases.
PI can be measured inexpensively and are accessible at hand during routine blood counts.
“Giant platelet” is a term used to describe platelets that are abnormally large, i.e., as large as a normal red blood cell. These may be seen in certain disorders such as immune thrombocytopenic purpura or in rare inherited disorders such as Bernard-Soulier disease.
Immature platelet fraction (IPF) is the percentage of immature platelets (also called reticulated platelets) circulating in the blood. It is one of the values reported when blood is evaluated using an automated instrument. The IPF may be used to determine if platelet production is increasing in cases of a low platelet count.
Platelets are produced in the bone marrow and are normally not released into the bloodstream until they have matured. When your platelet count is low (thrombocytopenia), the bone marrow is stimulated to produce platelets faster. When the need is great and when production cannot keep up with “demand,” then an increased number of immature platelets, often large platelets are released into the bloodstream.
- A low IPF indicates that the bone marrow is producing fewer platelets.
- An increased IPF indicates an increased loss of platelets in the blood, generally due to platelet destruction as seen in immune thrombocytopenia (ITP).
Lab test results including platelet count and IPF can also be used to help determine if you need a platelet transfusion and to help monitor bone marrow recovery, such as after a bone marrow transplant.
Table 2. Platelet indices with their normal range and their diagnostic and prognostic value in selected conditions.
| Platelet Indices (PI) | Normal range | Conditions with platelet indices above normal range | Conditions with platelet indices below normal range |
| MPV | 7.2-11.7 fL | –
immune thrombocytopenia purpura (ITP) – diabetes mellitus – DM related retinopathy and nephropathy – skeptic shock – heart disease – malignant tumors – complicated acute appendicitis |
–
non-complicated acute appendicitis – acute cholecystitis – low-grade inflammation ex. rheumatoid arthritis – threatened preterm labor |
| PDW | 8.3-56.6% | –
DM related retinopathy and nephropathy. – ST-elevation myocardial infarction – acute cholecystitis – threatened preterm labor – vaso-occlusive crisis sickle cell disease |
–
non- malignant tumors |
| P-LCR | 15-35% | –
immune thrombocytopenia purpura (ITP) – DM related retinopathy and nephropathy |
–
myeloid insufficiency |
| PCT | 0.22-0.24% | –
acute cholecystitis – active Crohn’s Disease with low hs-CRP |
–
immune thrombocytopenia purpura (ITP). |
FURTHER READING:
Karolina P, Anna K, Maryna K, -Rybak M, Sawicka,Ż,: Characteristics of platelet indices and their prognostic significance in selected medical condition – a systematic review. Advances in Medical Sciences 2020, 65, 2, pp 310-31
