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The Working Group Preanalytical Phase of the European Federation of Clinical Chemistry and Laboratory Medicine advises suppressing haemolysis-sensitive tests when haemolysis is clinically significant, as improper specimen handling can rupture red blood cells, increasing potassium levels. Thus, a correctly repeated blood sample should show lower potassium levels than a haemolysed one. This study aimed to determine the prevalence of haemolysed samples with potassium levels below the reference range and whether this predicts hypokalemia in repeated collections. From March 2022 to March 2024, 396,640 non-haemolysed samples (H-index < 2 UA) were analyzed. Samples with an H-index ≥ 2 AU were classified as haemolysed, and potassium values were suppressed. Warnings were issued for haemolysed samples with potassium below the reference range (3.4-4.5 mmol/L), advising new sample collection. Twenty-five (0.01%) repeat samples were taken within 24 hours of a previously haemolysed sample with low potassium. Severe and moderate hypokalemia were more common in these repeats, with severe hypokalemia (≤2.5 mmol/L) found in 48% of repeat tests, compared to 0.3% in all samples. Though rare, a decrease in potassium in haemolysed samples often precedes hypokalemia diagnosis. Implementing a simple and cost-effective LIS algorithm to alert clinicians could potentially reduce diagnosis and treatment time.

Pheochromocytoma and paraganglioma are neuroendocrine tumors characterized by a catecholamine production potential. The biochemical diagnosis for this type of tumor is carried out through the metanephrine titration on 24-hours urines. Some authors have suggested that the sensitivity of the test could be improved by sampling and analyzing urines 3 days in a row (cycle) versus a unique measurement but this method has never been fully evaluated. The goal of this study was to establish a comparison of diagnosis performances between urinary metanephrines measurement for 3 consecutive days, and metanephrines measurement on a unique 24-hour sample. Patients of Brest Regional University Hospital whose 3-consecutive day 24-hour urine samples had been analyzed from January 2011 to May 2017 were included in this study. The primary endpoint was the comparison of diagnostic performances of urinary metanephrine titration over a single day versus 3 consecutive days. Eighty-two patients for a total of 103 cycles among which 7 revealed a pheochromocytoma were analyzed. ROC curve analysis shows that the metanephrine cycle titration method is more efficient than the metanephrine single titration method (metanephrine: AUC=0.881 against 0.826 respectively; normetanephrine: AUC=0.946 against 0.901 respectively). Urinary titration over 3 days allows the diagnosis of 100% (7/7) of pheochromocytomas against 85.7% (6/7) for the the single urinary titration. In conclusion, metanephrine titration over 3 consecutive days of 24-hours urine samples shows a better sensitivity and better diagnosis performances for detecting pheochromocytoma and paraganglioma than the single titration method.