Practice and performance of lupus anticoagulant tests: A single centre experience

INTRODUCTION

Lupus anticoagulant (LA) is a well-known risk factor for thrombosis. Correct diagnosis of LA is essential in patient management with anticoagulation. The objectives of this study were to document the clinical and laboratory characteristics of patients tested for LA and to evaluate existing LA testing methods in our laboratory with the aim of improving the performance of LA test interpretation and reporting.

METHODS

Tests for LA include dilute Russell's viper venom time (dRVVT) and Kaolin clotting time (KCT). Patients with LA ratio (dRVVT screen ratio/dRVVT confirm ratio) of ≥1.2 were considered as LA positive irrespective of KCT results. KCT was considered positive if there was a prolongation in KCT screening test which was not corrected on mixing with normal plasma.

RESULTS

Of 577 patients' results, 295 were normal, 178 were KCT positive with negative dRVVT and 104 were LA positive. Incidences of thrombosis, connective tissue disease (CTD) and bad obstetric events were noted in 13%, 16% and 44% of normal patients, 9%, 22% and 49% of KCT+ patients and 23%, 37% and 17% of LA+ patients respectively. On further evaluation of dRVVT screen ratios, 431 had a ratio of <1.1, 59 had a ratio between 1.1 and 1.2 and 87 had a ratio of >1.2. Positive LA results were found in 3%, 29% and 87% of patients with dRVVT screen ratios of <1.1, 1.1 - 1.2 and >1.2 respectively.

CONCLUSION

LA+ patients had higher incidences of thrombosis and CTD as compared to normal and KCT only positive patients. There was no significant difference in clinical characteristics between normal and KCT+ patients which suggests the presence of a high rate of false-positive KCT results. Since confirmatory testing for KCT is not widely used, the option of using another LA screening test method should be considered. In regard to dRVVT testing, confirmatory test should only be performed in patients with prolonged dRVVT screening result which was not corrected upon mixing with normal plasma as required by the International Society of Thrombosis and Haemostasis guidelines on LA testing. This practice will not only result in significant cost reduction but also avoid diagnostic confusion.

A new complex translocation (8;22;21)(q22;q12;q22) in RUNX1/RUNX1T1 acute myeloid leukaemia

INTRODUCTION

Acute myeloid leukaemia (AML) with t(8;21)(q22;q22) producing RUNX1-RUNX1T1 rearrangement is a distinct sub-type which is usually associated with a favourable clinical outcome. Variant forms of t(8;21) are rare. Herein we describe a novel variant of t(8;21) AML in a 25-year-old pregnant woman who presented with intermittent fever.

CASE REPORT

Her peripheral smear and bone marrow aspirate showed many myeloblasts. Chromosomal study revealed t(8;22;21)(q22;q12;q22) and loss of X chromosome. Fluorescence in situ hybridization (FISH) using whole chromosome painting probes confirmed the three-way translocation involving chromosomes 8, 21 and 22. RUNX1-RUNX1T1 rearrangement was identified in FISH and reverse transcriptase polymerase chain reaction confirming the diagnosis of AML with variant t(8;21). The patient was treated with standard chemotherapy. She achieved morphological remission one month after induction chemotherapy.

DISCUSSION

Although the clinical significance of variant t(8;21) is not well delineated, the evaluation of 31 such cases suggests patients with variant t(8;21) have similar prognosis to those with classical t(8;21).

Severe asymptomatic hypophosphataemia in a child with T-acute lymphoblastic leukaemia

Hypophosphataemia is a metabolic disorder that is commonly encountered in critically ill patients. Phosphate has many roles in physiological functions, thus the depletion of serum phosphate could lead to impairment in multiple organ systems, which include the respiratory, cardiovascular, neurological and muscular systems and haematological and metabolic functions. Hypophosphataemia is defined as plasma phosphate level below 0.80 mmol per litre (mmol/L) and can be further divided into subgroups of mild (plasma phosphate of 0.66 to 0.79 mmol/L), moderate (plasma phosphate of 0.32 to 0.65 mmol/L) and severe (plasma phosphate of less than 0.32 mmol/L). The causes of hypophosphataemia include inadequate phosphate intake, decreased intestinal absorption, gastrointestinal or renal phosphate loss, and redistribution of phosphate into cells. Symptomatic hypophosphataemia associated with haematological malignancies has been reported infrequently. We report here a case of asymptomatic severe hypophosphataemia in a child with acute T-cell lymphoblastic leukaemia. A 14-year-old Chinese boy was diagnosed to have acute T cell lymphoblastic leukaemia (ALL). His serum biochemistry results were normal except inorganic phosphate and lactate dehydrogenase levels. The serum inorganic phosphate level was 0.1mmol/L and the level was low on repeated analysis. The child had no symptoms related to low phosphate levels. The possible causes of low phosphate were ruled out and urine Tmp/GFR was normal. Chemotherapy regime was started and the serum phosphate levels started to increase. Hypophosphataemia in leukaemia was attributed to shift of phosphorus into leukemic cells and excessive cellular phosphate consumption by rapidly proliferating cells. Several reports of symptomatic hypophosphataemia in myelogenous and lymphoblastic leukaemia in adults have been reported. To our knowledge this is the first case of severe asymptomatic hypophosphataemia in a child with ALL.

Modification to reporting of qualitative fluorescent spot test results improves detection of glucose-6-phosphate dehydrogenase (G6PD)-deficient heterozygote female newborns

INTRODUCTION

The glucose-6-phosphate dehydrogenase (G6PD) fluorescent spot test (FST) is a useful screening test for G6PD deficiency, but is unable to detect heterozygote G6PD-deficient females. We sought to identify whether reporting intermediate fluorescence in addition to absent and bright fluorescence on FST would improve identification of mildly deficient female heterozygotes.

METHODS

A total of 1266 cord blood samples (705 male, 561 female) were screened for G6PD deficiency using FST (in-house method) and a quantitative enzyme assay. Fluorescence intensity of the FST was graded as either absent, intermediate or normal. Samples identified as showing absent or intermediate fluorescence on FST were analysed for the presence of G6PD mutations using TaqMan@SNP genotyping assays and direct nucleotide sequencing.

RESULTS

Of the 1266 samples, 87 samples were found to be intermediate or deficient by FST (49 deficient, 38 intermediate). Of the 49 deficient samples, 48 had G6PD enzyme activity of ≤ 9.5 U/g Hb and one sample had normal enzyme activity. All 38 intermediate samples were from females. Of these, 21 had G6PD activity of between 20% and 60%, and 17 samples showed normal G6PD activity. Twenty-seven of the 38 samples were available for mutation analysis of which 13 had normal G6PD activity. Eleven of the 13 samples with normal G6PD activity had identifiable G6PD mutations.

CONCLUSION

Glucose-6-phosphate dehydrogenase heterozygote females cannot be identified by FST if fluorescence is reported as absent or present. Distinguishing samples with intermediate fluorescence from absent and bright fluorescence improves detection of heterozygote females with mild G6PD deficiency. Mutational studies confirmed that 85% of intermediate samples with normal enzyme activity had identifiable G6PD mutations.