Browsing by Author "Hoffmann, Mariza"

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    Case report : an index of suspicion in hyponatraemia
    (Hrvatsko društvo za medicinsku biokemiju, 2019) Barkhuizen, Marizna; Hoffmann, Mariza; Zöllner, Ekkehard W. A.; Erasmus, Rajiv T.; Zemlin, Annalise E.
    Serum indices can give valuable information and should be interpreted as a result. Lipaemia can influence results through different mechanisms, an important one being the electrolyte exclusion effect. A case of pseudohyponatraemia due to this is reported. A 15-year-old female with type 2 diabetes was seen for follow-up. Her biochemistry results revealed severe hyponatraemia of 118 mmol/L. Her capillary glucose concentration was 13.7 mmol/L with a corrected sodium of 122 mmol/L. A lipaemic index of 3+ (absolute value 1320) was noted, which was not flagged by the laboratory information system, as it was below the critical lipaemia limit for sodium determination. Repeated analysis of the same sample using a direct ion selective electrode method, the serum sodium concentration was 134 mmol/L (sodium corrected for glucose = 138 mmol/L). A triglyceride concentration was requested, which was severely raised (100.1 mmol/L). The electrolyte exclusion effect is an analytical phenomenon that causes falsely low electrolyte concentrations in the presence of severe lipaemia or hyperproteinaemia when using indirect analytical methods. These methods are used on many modern-day automated chemistry analysers and should be considered in a patient with asymptomatic hyponatraemia.
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    The role of point-of-care blood testing for ketones in the diagnosis of diabetic ketoacidosis
    (Health and Medical Publishing Group, 2015) Coetzee, Ankia; Hoffmann, Mariza; Ascott-Evans, Brynne
    Background. Urine dipstick testing for ketones is widely used when diabetic ketoacidosis (DKA) is suspected in patients with hyperglycaemia. If urinary ketones are positive, patients are referred for further management – often inappropriately, as the test is a poor surrogate for plasma ketones. Plasma beta-hydroxybutyrate (β-OHB) levels >3 mmol/L are diagnostic of DKA, while levels <1 mmol/L are insignificant. Objectives. To evaluate a hand-held electrochemical (point-of-care testing; POCT) ketone monitor and compare it with the gold-standard manual enzymatic method (MEM) for detection of plasma ketones. Methods. In a prospective and comparative study, we evaluated the measurement of β-OHB by means of POCT and the MEM in 61 consecutive samples from patients with suspected DKA at Tygerberg and Karl Bremer hospitals, Cape Town, South Africa. Capillary (for POCT) and plasma samples (for the MEM) were obtained simultaneously and compared for accuracy. Precision was assessed with control samples. Results. The POCT method was precise (coefficient of variation <4.5%), and there was a good correlation between the two methods (r=0.95). Regression analysis showed a proportional bias, with POCT reading higher than the MEM. However, when assessed at the relevant medical decision limits (β-OHB >3 mmol/L and <1 mmol/L), the total allowable error (bias + imprecision) was not exceeded. Patients will therefore still be classified correctly. The POCT method had a sensitivity of 100% and specificity of 89% for DKA (β-OHB >3 mmol/L), while at levels <1 mmol/L sensitivity was 100% and specificity 87.5%. Conclusion. The POCT device provides an accurate and precise result and can be used as an alternative to the MEM in the diagnosis of DKA.