Christine A. Holtkamp

Prednisone therapy for children with newly diagnosed idiopathic thrombocytopenic purpura. A randomized clinical trial.

The efficacy of corticosteroids in childhood acute idiopathic thrombocytopenic purpura (ITP) is controversial and has infrequently been evaluated in a controlled randomized fashion. We administered prednisone (2 mg/ kg/day for 14 days with subsequent tapering and discontinuation by day 21) or placebo to 27 children, aged 10 years or less, with newly diagnosed ITP. Platelet count, bleeding time (a test of the integrity of the platelet-microvasculature interaction), and clinical bleeding score (based on a 0–4 scale) were determined before (day 0) and six times following initiation of drug therapy (days 1–2, 3–5, 7, 14, 21, and 28). There were no statistically significant (p < 0.05) differences between the two treatment groups in any of the three study parameters except on day 7 of therapy when children receiving prednisone had higher platelet counts and lower bleeding scores and bleeding times than those taking placebo. Bleeding time correlated inversely with the platelet count in both treatment groups. Prednisone did not appear to influence bleeding time independent of its effect on platelet count. This treatment regimen of prednisone did not clearly improve hemostasis in childhood acute ITP except transiently at the end of 1 week of treatment.

Evidence against enhanced platelet activity in sickle cell anaemia

Summary. Although numerous studies have provided indirect evidence for enhanced platelet activity in sickle cell anaemia, little attention has been directed to examination of platelet alpha and dense granule release in the sickling disorders. We simultaneously measured by radioimmunoassay plasma levels of the alpha granule constituents β‐thromboglobulin (β‐TG) and platelet factor 4 (PF4) in 43 children with sickle cell anaemia in steady state and 24 patients during severe vaso‐occlusive crisis. β‐TG levels during steady state (50 ± 3.6 ng/ml, mean ± SEM) were greater (P<0.001) than in normal controls (36 ± 1.6), but there was no additional significant rise during crisis (55 ± 5.9). PF4 levels were similar (P= 0.12) in both steady state (10 ± 1.2 ng/ml) and crisis (9.3 ± 2.3) to those of normal controls (6.0 ± 0.8). The similarity of β‐TG/PF4 ratios in normal and sickle cell anaemia patients as well as the positive correlation (P<0.05) between platelet count and β‐TG and PF4 suggested that an artefactual in vitro platelet activation was responsible for some of the observed increased β‐TG and PF4 levels. Further evidence against enhanced platelet activity in these sickle cell patients included normal intraplatelet content of the dense granule constituent 5‐HT and a normal ATP/ADP ratio. From this data we conclude that platelet activation in children with sickle cell anaemia appears minimal.

The bleeding time may be longer in children than in adults

The bleeding time, the most frequently performed test reflecting in vivo platelet function, is the duration of blood flow from a standardized incision on the volar surface of the forearm. Normal values have been determined in adult subjects, but with the exception of neonates, data on the range of bleeding time values in pediatric patients are unavailable. Standard hematology textbooks imply that bleeding time values in children are similar to those of adults. We have reviewed our 9 years of experience with 137 children (mean age 6.5 years) who were referred for diagnostic evaluation of a bleeding disorder but whose history and physical examination were felt by us to be inconsistent with an abnormality of hemostasis. Bleeding time values in these individuals (mean 6.0 min, 95th percentile 9.0 min) were compared with those of 85 normal adult volunteers (mean 4.4 min, 95th percentile 6.5 min). The Simplate-I disposable device and vertical (perpendicular to elbow crease) incision direction were used in both groups. This difference between the pediatric and adult bleeding time values is statistically significant (p less than 0.0001). Neither age nor sex had a significant effect on the pediatric bleeding time measurements. We conclude that the bleeding time, when performed as described, is longer in children than in adults and that pediatric standards for bleeding time should be used in order to avoid a spurious diagnosis of a primary hemostatic disorder in some normal children.

Racial Differences in Ristocetin-induced Platelet Aggregation

Summary. Several investigators have reported defective ristocetin‐induced platelet aggregation (RIPA) in individuals whose red blood cells contain sickle haemoglobin, but the race of control subjects in these studies was not stated. Therefore, maximal amplitude of RIPA was examined in 75 normal whites and blacks, 16 of whom had sickle trait defined by haemoglobin electrophoresis and sickle prep. Final ristocetin concentrations in platelet rich plasma were 1·1,1·2 and 1·5 mg/ml. Mean aggregation at 1·1 mg/ml was significantly less in blacks (mean 31%) than in whites (mean 72%) (P < 0·001). 60% of blacks but only 11% of whites had less than 50% RIPA at 1·1 mg/ml. RIPA was entirely absent in 19% of blacks. Differences in RIPA between black and white subjects were also present at ristocetin concentrations of 1·2 and 1·5 mg/ml but were less striking. RIPA in 25 children with homozygous sickle cell anaemia was similar to that in the normal AA and AS blacks. Differences in RIPA could not be explained by age, sex, presence of sickle haemoglobin, or medications. Addition of normal plasma or platelets did not correct reduced RIPA in seven blacks, and their plasma inhibited normal RIPA responses.

Splenic reticuloendothelial function in children with cancer

We studied splenic function in children with cancer by quantitation of pitted, or pocked, erythrocytes (pocked RBC count), that is, the percentage of erythrocytes containing one or more membrane-bound vesicles, as determined by phase interference microscopy. The mean pocked RBC count in 93 normal children and adults was 0.49% (range 0% to 2.0%), with only 2.4% of normal subjects having values greater than 1.5%. Mean pocked RBC count in 28 children after splenectomy was 37% (range 3.2% to 81%). Among 181 children with cancer (525 specimens), the mean pocked RBC count was 1.06% (range 0% to 12.6%). Fifty-nine (32%) patients had one or more values greater than 1.5%, and 25 (13.8%) children had measurements greater than 3.0%, a level previously suggested to have clinical significance. Elevated pocked RBC counts (greater than 1.5%) occurred in more than one third of children with Wilms tumor and acute lymphoblastic leukemia, and in both patients with juvenile chronic myelogenous leukemia. Elevations in pocked RBC counts were not related to specific chemotherapy regimens or to disease activity. Mild splenic reticuloendothelial hypofunction occurs in many children with cancer and may contribute to the risk of infection in these patients.

RECOMBINANT GLYCOPROTEIN (GP)IIIa OLIGOPEPTIDES REACT WITH PLATELET AUTOANTIBODIES. ▴ 897

RECOMBINANT GLYCOPROTEIN (GP)IIIa OLIGOPEPTIDES REACT WITH PLATELET AUTOANTIBODIES. ▴ 897

888 FORMATION AND REMOVAL OF POCKED ERYTHROCYTES STUDIES IN HUMAN SUBJECTS AND LABORATORY ANIMALS

The “pit count” or pocked erythrocyte (Pk RBC) count (PC) is the percentage of RBCs containing one or more vesicles visualized by phase interference microscopy. The PC is <1.5% in normal subjects and 25-60% in surgically splenectomized patients; values between these extremes may result from splenic hypofunction. Although the PC is being increasingly utilized as a test of splenic function, little information is available about the patterns of formation and removal of these organelles. We performed serial PCs following splenectomy (S) in 4 patients. Levels began to rise within 1 week and reached a plateau (30-50%) by 6 to 8 weeks. Similar results were obtained following S of dogs, except that the steady state plateau value was only 10-13%. Rats initially exhibited a similar pattern of rise in PC post-S, but from the 4th to 10th week the PC gradually declined to 3%; splenosis or accessory spleens were not visualized at autopsy. Rabbits had only a slight and inconsistent rise in PC after S. Rate of removal from the circulation of Pk RBCs was determined by exchange transfusion of blood from a splenectomized dog into a eusplenic animal. Clearance of the Pk RBCs was linear, with a t1/2 of 8 hours. We conclude that Pk RBCs rise slowly following S, rapidly disappear from the circulation in the presence of a normal spleen, and vary in the pattern of rise and peak levels following S among different animals.

795 PLATELET FUNCTION IN CHILDHOOD IDIOPATHIC THROMBOCYTOPENIC PURPURA (ITP)

The risk of hemorrhage in ITP is related not only to the platelet count but also to the functional integrity of the platelets and microvasculature. Platelet function in adults with ITP has been reported by different investigators to either be enhanced (bleeding time (BT) shorter than expected for the degree of thrombocytopenia) or impaired (defective aggregation due to effects of anti-platelet antibody). These discrepant results are unexplained and data in pediatric patients are lacking.Therefore, we investigated platelet function in 46 children with acute ITP by modified template BT and in 22 children with chronic ITP by BT, platelet aggregation in response to epinephrine, collagen and ADP, and/or generation of malondialdehyde (MDA) following exposure of platelets to N-ethylmaleimide. BT, performed on 185 occasions in the 68 patients, was nearly always prolonged (> 7 1/2 minutes) when the platelet count was under 100,000/μl and markedly prolonged (> 25 minutes) in 52% of children whose platelet counts were < 20,000/μl. BT values in the patients with ITP were not different from those in 20 children with thrombocytopenia due to decreased platelet production. BT was not affected by corticosteroid therapy independent of platelet count. Platelet aggregation and MDA measurements performed on 18 occasions in 12 patients with chronic ITP were usually normal. We conclude that platelet reactivity is neither enhanced nor significantly impaired in childhood ITP.

PROLONGED BLEEDING TIME IN CHILDREN AND YOUNG ADULTS WITH HEMOPHILIA

Of 49 patients with hemophilia A or B, who had not received replacement transfusions for at least 72 hours, ten were demonstrated to have a prolonged value for the bleeding time. None had evidence of von Willebrands disease or prior aspirin ingestion, and only one was found to have an associated intrinsic platelet defect. It appears that the bleeding time, generally thought to be a measurement of platelet-subendothelium interaction, may also sometimes be prolonged in congenital coagulation disorders in which platelet function is normal.