Pseudohyperkalaemia is a common finding in myeloproliferative disorders that may lead to inappropriate management of patients.

Pseudohyperkalaemia in conditions with increased platelet counts is caused by an in vitro rise of the serum potassium concentration during whole blood coagulation and the lysis of the platelets and other cellular components, in the presence of normal renal function and normal plasma potassium levels. The association between pseudohyperkalaemia and aetiology of thrombocytosis was studied in a 6-year retrospective audit on 90 patients with thrombocytosis referred to the Haematology Department in Ulster Hospital Dundonald, a large district general hospital. Over two-thirds of this study population had myeloproliferative disorders, and the most common diagnosis was primary thrombocythaemia (41%, n = 37). Reactive thrombocytosis was observed in approximately one-third of the cases (32%, n = 29). Pseudohyperkalaemia with apparent potassium level above the upper limit of the normal range (reference range K 3.5-5.1 mmol/l) was observed in the majority of patients with thrombocytosis from any aetiology (60%, n = 54). The likelihood of finding pseudohyperkalaemia was highest among patients with primary thrombocythaemia (75.7%, n = 28/37) and polythaemia rubra vera (75%, n = 12/16), followed by myelofibrosis (50%, 4/8) and reactive thrombocytosis (34.5%, n = 10/29). A highly significant positive correlation was observed between the platelet counts and the serum potassium level (Spearman's correlation coefficient, R = 0.998, P = 0.01). Awareness of pseudohyperkalemia in disease conditions with increased platelet counts will lead to the withholding of potentially harmful treatment.

Novel and Mediterranean beta thalassemia mutations in the indigenous Northern Ireland population.

beta thalassemia is one of the most common genetic diseases worldwide resulting from aberrant beta-globin chain production. It is highly prevalent in regions with endemic malaria, but it is also present at low frequency in the indigenous populations of non-tropical areas such as Britain. Screening beta thalassemia trait individuals from Northern Ireland has detected 2 Mediterranean mutations, 39 (C --> T) and IVS-I-110 (G --> A); the previously reported IVS-II-850 (G --> A) mutation originally described in individuals of Scottish/English ancestry; and 2 novel mutations, initiation codon A --> C and 109 delG. Haplotype analysis indicates that the Mediterranean mutations are present on previously described haplotypes, suggesting that they have arisen due to migration. It remains to be established whether the novel mutations have arisen de novo in Northern Ireland.

Efficacy and response to intravenous anti-D immunoglobulin in chronic idiopathic thrombocytopenic purpura.

This review explored the effectiveness of anti-D in the management of chronic idiopathic thrombocytopenic purpura (ITP). Of 16 patients, 14 non-splenectomized and two splenectomized, with chronic ITP received anti-D immunoglobulin at a dose of 50-75 mcg/kg. A total number of 100 doses anti-D were given. Fourteen patients had previous treatment with steroids, which was discontinued either because of unresponsiveness or unacceptably high maintenance doses. Two patients had no previous treatments with any modality. Anti-D was given as a short i.v. infusion whenever platelet count dropped below 30 x 10(9)/l or patient was haemorrhagic or preoperatively. Response was defined as an absolute platelet count >30 x 10(9)/l or an increment by > or =20 x 10(9)/l. Response was obtained in 14 patients with a response rate of 87%. Fifteen patients were not on any other form of treatment at the time of anti-D therapy and one patient had a concurrent steroid therapy. The improvement in platelet count lasted for more than 8 weeks post-57% of anti-D infusions. We report two patients with previous splenectomy for ITP who responded to anti-D therapy. The side-effects profile was very mild with no patients required red cell transfusion.

B cell signet-ring cell lymphoma of bone marrow.

A case of signet-ring cell lymphoma affecting the bone marrow and diagnosed by bone marrow trephine biopsy is reported. Normal marrow was replaced totally by cells with large central vacuoles, many of which displaced the nucleus to the periphery of the cell, imparting a signet-ring appearance. Initially, the favoured morphological diagnosis was metastatic signet-ring adenocarcinoma, but on immunocytochemistry the tumour cells were strongly positive for CD45 (leucocyte common antigen) and the B cell marker CD20 (L26). Electron microscopy revealed electron-lucent vacuoles with no discernable internal structure. The tumour was classified as a high grade centroblastic lymphoma using the upgraded Kiel classification. Despite chemotherapeutic treatment, the patient died during an episode of septicaemic shock within two months of presentation.

Successful remission induction with deoxycoformycin in elderly patients with T-helper prolymphocytic leukaemia.

Two elderly patients with prolymphocytic leukaemia (PLL) of T helper phenotype were treated with the adenosine deaminase inhibitor--deoxycoformycin--and achieved remission. The first patient has remained in an unmaintained remission for over a year. The second patient, treated with a regime which produced less side effects, subsequently relapsed in skin and lymph nodes and died. In view of the rarity of this condition a multi-centre assessment of the effectiveness of deoxycoformycin is indicated. T-lymphocyte colony formation in both cases was found to be reduced. Co-culture of the patients' lymphocytes with nonadherent mononuclear cells from normal individuals also showed inhibition of T-colony formation indicating that lack of nutrients or accessory cells was not responsible for low T-colony forming capacity.