Automated counting of platelets on the Bayer ADVIA 120 analyser.

Precise counting of platelets is difficult particularly in the low thrombocytopenic range or when large platelets exist. The recently available Bayer ADVIA 120 analyser uses a method of counting platelets based on two dimensional laser light scatter. We have evaluated this technique on an analysis of 217 peripheral blood samples and found significant differences in platelet counts compared with values obtained by impedance technology, when the causes of thrombocytopenia were due to peripheral platelet consumption. Moreover, such differences were more marked in those samples from severely thrombocytopenic individuals with large platelets on the blood film. These differences, which warrant further study, may have significant implications for the management of patients with very low platelet counts.     

Thrombocytopenia model with minimal manipulation of blood cells allowing whole blood assessment of platelet function

In vitro models of thrombocytopenia are useful research tools. Previously published models have shortcomings altering properties of platelets and other blood components. The aim of the present study was to develop a whole blood method to induce thrombocytopenia with minimal manipulation, and to describe platelet function in induced thrombocytopenia in individuals with healthy platelets. Hirudin anticoagulated blood was obtained from 20 healthy volunteers. One part of the blood was gently centrifuged at 130g for 15 minutes. The platelet-rich plasma was replaced with phosphate-buffered saline to establish thrombocytopenia. Various levels of thrombocytopenia were achieved by combining different volumes of baseline whole blood and thrombocytopenic blood. Platelet counts were measured by flow cytometry (Navios, Beckman Coulter) and routine haematological analyser (Sysmex XE-5000). Platelet function was analysed by impedance aggregometry (Multiplate® Analyzer, Roche) and by flow cytometry (Navios, Beckman Coulter) using collagen, adenosine diphosphate, thrombin receptor activating peptide-6 and ristocetin as agonists. Median baseline platelet count was 227×10⁹/l. The in vitro model yielded median platelet counts at 51×10⁹/l (range 26–93×10⁹/l). We observed minor, yet significant, changes in platelet size and maturity from baseline to modelled thrombocytopenia. In the thrombocytopenic samples, significant and positive linear associations were found between platelet count and platelet aggregation across all agonists (all p-values<0.001). Platelet function assessed by flow cytometry showed minimal alterations in the thrombocytopenic samples. A new whole blood-based model of thrombocytopenia was established and validated. This new model serves as a useful future tool, particularly to explore platelet function in patients with thrombocytopenia.     

Automated Optical Counting of Blood Platelets

We have evaluated the use of an opticalparticle counter to perform automatedplatelet counts on whole blood. Theerythrocytes were lysed by dilution ofwhole blood with 2 M urea and the remaining platelets and leukocytes wereenumerated by a darkfield microscopeoptical system that detects light diffractedby them. A suspension of fixed humanplatelets available commercially washighly satisfactory for standardization.The method gave accurate and reproducible platelet counts, comparable withthose of electronic particle counting onvenous blood and substantially morereliable platelet counts on thrombocytopenic and finger-puncture blood samples. We believe that errors resultingfrom the electronic method were causedby technical difficulties of sample handling and not to an intrinsic error in electronic counting. By using the automatedoptical method we found no significantdifference between the platelet counts ofcapillary and venous blood, althoughcapillary platelet counts had twice thevariability of venous counts. The opticaltechnique has important advantages overelectronic platelet counting, and itssuperiority appears to be due to the ability to count platelets in diluted wholeblood rather than in plasma. It shouldprove especially useful in performing thelarge numbers of platelet counts onthrombocytopenic and finger-punctureblood samples that are increasingly important for management of patients receiving chemotherapy.

Submitted on April 20, 1971 Revised on May 21, 1971 Accepted on May 25, 1971     

Accuracy of platelet counting haematology analysers in severe thrombocytopenia and potential impact on platelet transfusion

Although haematology analysers provide reliable full blood counts, they are known to be inaccurate at enumerating platelets in severe thrombocytopenia. If the thresholds for platelet transfusion, currently set at 10 x 10(9)/l, are to be further reduced, it is vital that the limitations of current analysers are fully understood. The aim of this large multicentre study was to determine the accuracy of haematology analysers in current routine practice for platelet counts below 20 x 10(9)/l. Platelet counts estimated by analysers using optical, impedance and immunological methods were compared with the International Reference Method for platelet counting. The results demonstrated variation in platelet counting between different analysers and even the same type of analyser at different sites. Optical methods for platelet counting on the XE 2100, Advia 120, Cell-Dyn 4000 and H3* were not superior to impedance methods on the XE 2100, LH750 and Pentra analysers. All analysers except one overestimated the platelet count, which would result in under transfusion of platelets. This study highlights the inaccuracies of haematology analysers in platelet counting in severe thrombocytopenia. It re-emphasizes the need for external quality control to improve analyser calibration for samples with low platelet counts, and suggests that the optimal thresholds for prophylactic platelet transfusions should be re-evaluated.     

Reticulated platelet counts in patients undergoing autologous bone marrow transplantation: An aid in assessing marrow recovery

Thiazole orange (TO) is a fluorescent dye that is commonly used for flow cytometric measurement of erythrocytic reticulocytes. This technique has also been validated for counting “reticulated” platelets, as a measure of bone marrow thrombopoietic activity. Patients with an established diagnosis of idiopathic thrombocytopenic purpura (ITP) have been reported to have a three- to five-fold increase in the percent of circulating reticulated platelets. The current study was conducted to determine if platelet reticulocyte counts predicted recovery of bone marrow thrombopoietic activity following autologous bone marrow transplantation. We found an increase in the percent of circulating reticulated platelets preceding recovery of the platelet count; then, as the patients' platelet counts rose, the percent reticulated platelets fell. In patients with prolonged thrombocytopenia, a persistent increase in the proportion of reticulated platelets suggested a consumptive process, as opposed to failure of engraftment. Moderate transfusion of platelet concentrates did not interfere with the ability of the platelet reticulocyte measurements to detect increased thrombopoietic activity. Platelet transfusions did obscure any decrease in the proportion of reticulated platelets. Our results show that platelet reticulocyte counts could be useful in monitoring the recovery of marrow function following autologous bone marrow transplantation. © 1994 Wiley-Liss, Inc.     

Platelet satellitism and phagocytosis by neutrophils: Association with antiplatelet antibodies and lymphoma

Satellitism and phagocytosis of platelets by neutrophils in EDTA anticoagulated blood have been considered in vitro phenomena without clinical significance. We observed these in a patient with acute, severe thrombocytopenic purpura who subsequently proved to have malignant lymphoma. Wide oscillations in the platelet count were noted and recurrent, severe gastrointestinal bleeding occurred even when the platelet count was normal. Platelet function was abnormal as shown by decreased platelet adhesion to glass beads, absence of a secondary wave of aggregation in response to ADP and epinephrine, and no aggregation with collagen. Suspension of control platelets in the patient's plasma induced similar aggregation defects in the control platelets. Combination chemotherapy resulted in regression of lymphadenopathy, but platelet abnormalities and bleeding persisted. Platelet satellitism and phagocytosis by neutrophils seen on peripheral blood films may be associated with true thrombocytopenia, abnormal platelet function and bleeding with an underlying systemic disease.     

Evaluation of platelet function in thrombocytopenia

Whole blood aggregometry is a functional assay for determination of platelet function. Until now, whole blood aggregometry has not been considered feasible at low platelet counts. Hence, the objectives of the present study were to explore platelet function in thrombocytopenia using a novel index of impedance aggregometry adjusted for platelet count and evaluate the association to platelet function assessed by flow cytometry. Hirudin anticoagulated blood was collected from 20 healthy volunteers, 20 patients with primary immune thrombocytopenia (ITP), and 17 hematological cancer patients. Platelet function was analyzed by impedance aggregometry and by flow cytometry. Collagen, adenosine diphosphate, thrombin receptor agonist peptide-6, and ristocetin were used as agonists for both analyses. Thrombocytopenia in healthy whole blood was induced in vitro employing a recently published method. Platelet aggregation of thrombocytopenic patients was evaluated relative to the aggregation of healthy volunteers at the same platelet count. In flow cytometry, platelet function was described as expression of the platelet surface glycoproteins: bound fibrinogen, CD63, and P-selectin. Similar platelet counts were obtained in the patient groups (p = 0.69) (range: 13–129 × 10⁹/l). Aggregation adjusted for platelet count was significantly increased in ITP patients compared to healthy platelets across all agonists. The platelet aggregation was high in the 95% prediction interval, with 18 ITP patients above the prediction interval in at least two agonists. In contrast, the platelet aggregation was low in the prediction interval in cancer patients, and three cancer patients with platelet aggregation below the prediction interval in at least one agonist. ITP patients displayed increased expression of bound fibrinogen and CD63 following activation, compared with particularly cancer patients, but also compared with healthy platelets. This study demonstrated the feasibility of a novel approach to perform platelet function analyses in thrombocytopenia using impedance aggregometry adjusted for platelet count.     

Variable levels of carry over on platelet counts < or = 20 x 10(9)/l with the Bayer Advia 120

Accurate platelet counts are essential for the safe management of severe thrombocytopenia (platelet counts < or = 20 x 10(9)/l). The effect of carry over on platelet counting in severe thrombocytopenia was investigated by performing counts before and after saline rinses on three Bayer Advia 120 automated blood counters. Counts were performed in both primary and manual closed tube system modes on two instruments and in manual open tube mode on a third. A total of 194 samples with platelet counts < or = 20 x 10(9)/l were studied. First counts were significantly higher in all groups. The magnitude of the difference varied both by analyser and counting mode. Carry over was minimal with one analyser in primary mode and second counts were on average only 5.5% lower; on a second analyser in manual closed tube system mode second counts were on average 37.7% lower. A first count of > or = 10 x 10(9)/l fell to <10 x 10(9)/l on the second count in 35 of 145 samples (24.1%). In five such samples, all tested on one analyser, the second count was <50% of the value of the first count. Two of 49 (4.1%) first counts of <10 x 10(9)/l increased to > or = 10 x 10(9)/l on repeat. These results show a variable and often potentially clinically important carry-over effect on severely thrombocytopenic samples using the Advia 120.     

Effective estimation of correct platelet counts in pseudothrombocytopenia using an alternative anticoagulant based on magnesium salt

Pseudothrombocytopenia remains a challenge in the haematological laboratory. The pre‐analytical problem that platelets tend to easily aggregate in vitro, giving rise to lower platelet counts, has been known since ethylenediamine‐tetra acetic acid EDTA and automated platelet counting procedures were introduced in the haematological laboratory. Different approaches to avoid the time and temperature dependent in vitro aggregation of platelets in the presence of EDTA were tested, but none of them proved optimal for routine purposes. Patients with unexpectedly low platelet counts or flagged for suspected aggregates, were selected and smears were examined for platelet aggregates. In these cases patients were asked to consent to the drawing of an additional sample of blood anti‐coagulated with a magnesium additive. Magnesium was used in the beginning of the last century as anticoagulant for microscopic platelet counts. Using this approach, we documented 44 patients with pseudothrombocytopenia. In all cases, platelet counts were markedly higher in samples anti‐coagulated with the magnesium containing anticoagulant when compared to EDTA‐anticoagulated blood samples. We conclude that in patients with known or suspected pseudothrombocytopenia the magnesium‐anticoagulant blood samples may be recommended for platelet counting.     

Problems with platelet counting in thrombocytopenia. A rapid manual method to measure low platelet counts.

Because most automated platelet counters cannot be relied on in thrombocytopenia, clinicians face a problem when decision making is based on platelet counts. Therefore we evaluated a visual platelet counting method from a blood smear with white blood cells (WBCs) as reference (PCW = platelet count based on WBC). Platelet counting for 74 thrombocytopenic (<120 x 10(9)/L) children was performed with PCW and with an automated counter (impedance principle); both methods were compared with evaluation by phase-contrast microscopy as the standard method. The PCW correlated well with the phase-contrast microscopy evaluation (y = -0.38 + 1.01x, r2 = 0.99). For platelet counts <20 x 10(9)/L the maximal deviation was 2 x 10(9)/L. The correlation between automated counts and the standard method was poor. The regression was y = 9.63 + 0.94x, r2 = 0.86. For platelet counts <20 x 10(9)/L the maximal deviation was 37 x 10(9)/L; on average, 7 x 10(9)/L platelets were counted in excess when compared with the standard method. PCW, in contrast to the automated impedance method, discriminated platelets from nonplatelet particles such as debris, fragments of red blood cells (hemolytic-uremic syndrome [HUS]) and of blast cells, and identified platelets of abnormal size. In addition, the appearance ofplatelets, WBCs, and RBCs gave clues to the etiology of thrombocytopenia, such as leukemia, infection, HUS, familial macrothrombocytopenia, and immune thrombocytopenia. PCW is a fast, reliable platelet counting method requiring less experience than the phase-contrast method. Visual evaluation from a stained smear clearly differentiates platelets and nonplatelet particles in contrast to most automated counters. In addition, the original smear can be preserved and reevaluated.     

Continuing developments with the automated platelet count

The four main procedures for platelet counting are: manual phase contrast microscopy, impedance, optical light scatter/fluorescence and flow cytometry. Early methods to enumerate platelets were inaccurate and irreproducible. The manual count is still recognized as the gold standard or reference method, and until very recently the calibration of platelet counts by the manufacturers of automated cell counters and quality control material was performed by this method. However, it is time-consuming and results in high levels of imprecision. The introduction of automated full blood counters using impedance technology resulted in a dramatic improvement in precision. However, impedance counts still have limitations as cell size analysis cannot discriminate platelets from other similar-sized particles. More recently, light scatter or fluorescence methods have been introduced for automated platelet counting, but there are still occasional cases where an accurate platelet count remains a challenge. Thus, there has been interest in the development of an improved reference procedure to enable optimization of automated platelet counting. This method utilizes monoclonal antibodies to platelet cell surface antigens conjugated to a suitable fluorophore. This permits the possible implementation of a new reference method to calibrate cell counters, assign values to calibrators, and to obtain a direct platelet count on a variety of pathological samples. In future, analysers may introduce additional platelet parameters; a reliable method to quantify immature or reticulated platelets would be useful.     

The Haemostatic Effect of 51Cr-Labelled Blood Platelets An Experimental Study in the Rabbit

The haemostatic effect of ⁵¹Cr-labelled platelets was studied in 5 rabbits made thrombocytopenic (35,000/μl blood) by whole body ionizing irradiation. Bleeding times were recorded after standardized cuts on the inner side of the rabbit's ear, a method with an acceptable reproducibility. The animals were then each transfused with concentrates of labelled platelets from 2 healthy donor rabbits. This increased the platelet counts to about 2 times 10⁵/μl blood. Bleeding time values were markably prolonged before transfusion and became normalized when tested 1 and 4 h after transfusion. In 3 control experiments, where unlabelled platelet rich plasma was transfused to thrombocytopenic recipients, a similar shortening of the bleeding time was observed. It is concluded that ⁵¹Cr-labelled platelets retain haemostatic ability comparable to non-labelled platelets, when circulating in a recipient animal.     

Chronic thrombocytopenia of childhood: use of non-invasive methods in clinical evaluation

OBJECTIVES: An unselected group of 21 children with chronic thrombocytopenia was investigated to understand the patients' platelet abnormality better. METHODS: Platelet counts, mean platelet volumes (MPV), membrane glycoproteins and Fcgamma receptor type IIA (FcgammaRIIA) polymorphism H131R, reticulated platelets (% RP), antiplatelet antibodies and plasma thrombopoietin (TPO) were measured. RESULTS: Sixteen patients had idiopathic thrombocytopenic purpura (ITP) (group 1: platelets < 50 x 10(9)/L, n = 6; group 2: 50-99 x 10(9)/L, n = 4; group 3: 100-149 x 10(9)/L, n = 4; group 4: splenectomised patients with normal platelet counts, n = 2). Five patients had familial thrombocytopenia. Six healthy children were studied as a reference. In the 19 thrombocytopenic patients, the platelets were significantly larger and % RP and TPO levels were significantly higher than those in the controls. Increased megakaryocytosis at diagnosis was associated with larger MPV and higher % RP but not with platelet level or TPO. The % RP was remarkably high in all ITP patients of group 1 indicating a brisk production of platelets despite low peripheral count. In all patients with familial thrombocytopenia, TPO was increased suggesting that the syndrome was not because of defective TPO production. The distribution of FcgammaRIIA alleles in the patients was similar to that in the controls. CONCLUSIONS: A combined application of % RP and TPO could be helpful in classifying patients with chronic thrombocytopenia into different categories. The observations may be of value in the clinical evaluation of ITP patients and lead to avoidance of invasive examinations at least in some patients.     

Garcia's Disease

After a critical study, a splenectomy was performed in a 6-year-old boy with chronic thrombocytopenic purpura. Failure of surgery and immunosuppressive therapy prompted new investigations which led to the discovery of a cyclic thrombocytopenic purpura related to a periodic variation in maturity of megakaryocytes. The patient's platelets were morphologically and functionally normal and it was not possible to demonstrate neither immunological mechanism, nutritional deficiency, influence of the environment nor consumption or excessive destruction of platelets. Cyclic thrombocytopenia was detected in the father and also cyclic variations in platelet counts from normal values to over 1,000 times 10⁹/1 in 4 of 9 siblings. In view of these findings. The abnormal condition in this family was named Garcia's disease.     

Effect of heparin on platelet count and platelet aggregation

The in vitro effect of heparin on platelet aggregation was studied in three groups: in 26 subjects recently treated with heparin, in 18 subjects on maintenance hemodialysis, and in 20 normal controls. With the aid of Technicon H6000, platelet counts and platelet aggregations were compared in whole blood samples collected in ethylenediaminetetraacetic acid (EDTA) and in heparinized tubes. Although there was no significant difference between platelet count of heparinized and EDTA blood in the control group, the dialysis group and the group recently treated with heparin showed significantly lower platelet counts and more platelet aggregation in heparinized tubes than in EDTA tubes. We speculate that the majority of subjects exposed to heparin develop an antibody or a proaggregator which can aggregate or agglutinate platelets in the presence of heparin and causes destruction of platelets; but only in a small percentage of subjects receiving heparin is this reaction severe enough to cause thrombocytopenia.     

Hypersplenic thrombocytopenia differentiated from increased peripheral destruction by platelet volume

Platelet volume distribution was examined in 16 patients with hepatosplenomegaly and platelet counts of 45 000 to 90 000/mm; 12 patients with autoimmune thrombocytopenia and randomly matched platelet counts; and 20 normal subjects. Five platelet volume variables of increasing platelet size were defined from the averages of 20 normal curves. Patients with hypersplenism had decreased volume values of 78% to 87% (mean, 83%) of the average normal population (P less than 0.001). Patients with autoimmune thrombocytopenic purpura had values significantly greater than normal by 124% to 149% (mean, 134%) (P less than 0.001). Patients with autoimmune thrombocytopenic purpura, when compared with hypersplenic patients, had significantly greater platelet volume values ranging from 154% to 174% (mean, 161%), P less than 0.001. We concluded that patients with hepatosplenomegaly have smaller platelets in their peripheral blood and a platelet volume distribution that can be distinguished easily from patients with autoimmune thrombocytopenic purpura, despite comparable platelet counts.     

Platelet Survival and Platelet Production in Idiopathic Thrombocytopenic Purpura (ITP)

S ummary . Platelet mean life span (MLS) and platelet production were measured in 3–5 patients with idiopathic thrombocytopenic purpura (ITP) and in 21 healthy subjects.
The mean platelet production in ITP was 2.3 times normal: the highest values were 3–5 times normal. There was a highly significant negative correlation between platelet production and peripheral platelet count. With platelet counts above 50000μl, platelet turnover was within the upper part of the normal range, but with lower platelet counts, turnover progressively increased. It is concluded that the bone marrow in ITP increases platelet production in response to a low platelet count and that this response does not differ from that hitherto known to occur in man and animals rendered thrombocytopenic by thrombopheresis.
The disappearance curve of ⁵¹Cr labelled platelets in ITP consists of two components, a rapid initial one covering the first 15 min after infusion and then a slower one. The pattern was the same whether autologous or homologous platelets were used for labelling. It is suggested that the initial part of the curve does not represent in vivo survival but is due to slight damage to the platelets during the labelling procedure. These slightly damaged cells can resume normal viability when infused into a normal recipient but are rendered less viable when further damaged by platelet antibodies in patients with ITP. This explains the low recovery of infused labelled platelets in ITP recipients, despite the fact that the size of their splenic platelet pool is normal.     

Cyclic thrombocytopenia in a patient treated with cyclosporine for refractory idiopathic thrombocytopenic purpura

Cyclic thrombocytopenia (CT) is a rare disorder with cyclic changes of the platelet counts. Though the pathogenesis of this disorder has not been clarified, recent reports suggest that periodic destruction and/or ineffective production of platelets may be important causes of the disease. We report a case of a patient with refractory idiopathic thrombocytopenic purpura (ITP) in whom CT developed after cyclosporine A (CyA) therapy. There was an inverse relation between platelet counts and the serum levels of platelet-associated immunoglobulin G (PAIgG). The ploidy of bone marrow megakaryocytes also had an inverse relation with platelet counts. When the platelet count was low, the ploidy of megakaryocytes increased (P < 0.01). The number and area of bone marrow megakaryocytes were unrelated to platelet counts. These results indicate the possibility of platelet destruction caused by immunological mechanisms in CT. Cyclosporine A could have certain but fluctuating regulatory effects against antibody production for circulating platelets, which could lead to cyclic changes of the platelet counts. This case also suggests that CyA can be effective in severe refractory ITP. Regulatory mechanisms of platelet production and destruction and appropriate doses of CyA should be further studied in autoimmune-mediated thrombocytopenias. Am. J. Hematol. 56:272–276, 1997. © 1997 Wiley-Liss, Inc.     

Enumeration of platelets by multiparameter flow cytometry using platelet-specific antibodies and fluorescent reference particles

Summary The correct enumeration of platelets is still an elusive matter. This is mainly due to the fact that commercial instruments which are used for platelet counting cannot discriminate platelets from other cellular particles and precipitates that cause similar signals. Visual (chamber counting) methods are still frequently used in routine laboratories to verify low automated platelet counts (< 50 × 10/l) despite obvious technical and statistical drawbacks. The following report shows how platelet counts can be measured by multiparameter flow cytometry with the help of reference particles (fluorescent latex beads) and platelet-specific antibodies i.e. anti-GPIIb/IIIa(CD41a), anti-GP Ib-α (CD42b) and anti-GP IIIa (CD61). The linearity of this method was highly satisfactory and the observed imprecision was within acceptable limits. At a platelet concentration of 10 × 10⁹/l the coefficient of variation (CV, n = 10) ranged from 5.3% (PCV = 0.456) to 5.6% (PCV = 0.148). Accuracy was evaluated by comparing results to the ICSH-selected method for platelet counting. The correlation of both methods was significant (P < 0.005) and Passing-Bablok's linear regression analysis showed no systematic differences between the two methods. Comparisons of this new platelet counting technique were also performed with routine visual methods, automated blood analysers (Technicon H-1, Sysmex E-5000) and a different flow cytometric method using only forward and side light scatter properties of platelets for their discrimination. The linear correlation of all methods was significant (P < 0.01) at platelet concentrations above 50 × 10⁹/l. At lower platelet concentrations, our new platelet counting technique correlated significantly only with the visual and the forward/side scatter methods. These findings stress the necessity to confirm low platelet counts by automated blood analysers and suggest that using multiparameter flow cytometry with platelet-specific antibodies may be a proficient way to do so. The possibility of using this technique as a reference method is discussed.     

Complement (C3) binding to platelets in autoimmune thrombocytopenia

Summary. In view of conflicting reports on the occurrence of complement binding to platelets in idiopathic autoimmune thrombocytopenic purpura (AITP) we performed measurements of platelet bound C3 in patients with AITP who had elevated levels of platelet bound IgG. Using a quantitative antiglobulin consumption technique 38 out of 42 patients were found to have fixed abnormally large amounts of C3 to their platelets, and a significant positive correlation between the amounts of platelet bound IgG and C3 was shown to exist. In additional experiments antibody eluates were prepared from AITP platelets and were shown to cause the fixation of C3 to normal donor platelets in vitro. Taken together these findings strongly suggest that the C3 binding in AITP is specifically related to the disease process.