Shing H Zhan1, Hamish Nicolson1, Alison Takahashi1, Andre Mattman2. 1. Department of Pathology and Laboratory Medicine, the University of British Columbia, Vancouver, Canada. 2. Department of Pathology and Laboratory Medicine, the University of British Columbia, Vancouver, Canada. Electronic address: amattman@providencehealth.bc.ca.
Abstract
BACKGROUND: Mean corpuscular volume (MCV) can be artefactually inflated, by variation in sodium concentration, on the Sysmex XE-2100. We report that severe hyperglycemia and modest lactic acidemia can also spuriously increase MCV. To catch and correct such inaccurate MCV measurements, we propose to flag them using commonly assayed biomarkers. MATERIALS AND METHODS: We examined the relationship between delta MCV (uncorrected MCV minus corrected MCV), plasma osmolality, and levels of plasma glucose, lactate, and sodium in 60 samples from emergency room patients. Based on these biomarkers, we developed and tested a preliminary composite flag system to identify high delta MCV on 105 ER samples. Finally, we evaluated a revised composite flagging system optimized to improve the positive predictive value. RESULTS: Plasma osmolality, glucose and lactate are each correlated with delta MCV. The revised composite flag system - based on ≥ 5.0 mmol/L of plasma lactate, > 32 mmol/L of glucose, or > 150 mmol/L of sodium - identified twice as many patients with spuriously elevated MCV as the vendor recommended MCHC flagging system. The associated positive predictive value of 31%, while lower than the vendor flagging system (62%), was considered adequate for implementation in our laboratory. CONCLUSIONS: We recommend reporting clinically significant corrected MCVs, based on sample pre-dilution with the Sysmex buffer, when the proposed composite metabolic flag is triggered.
BACKGROUND: Mean corpuscular volume (MCV) can be artefactually inflated, by variation in sodium concentration, on the Sysmex XE-2100. We report that severe hyperglycemia and modest lactic acidemia can also spuriously increase MCV. To catch and correct such inaccurate MCV measurements, we propose to flag them using commonly assayed biomarkers. MATERIALS AND METHODS: We examined the relationship between delta MCV (uncorrected MCV minus corrected MCV), plasma osmolality, and levels of plasma glucose, lactate, and sodium in 60 samples from emergency room patients. Based on these biomarkers, we developed and tested a preliminary composite flag system to identify high delta MCV on 105 ER samples. Finally, we evaluated a revised composite flagging system optimized to improve the positive predictive value. RESULTS: Plasma osmolality, glucose and lactate are each correlated with delta MCV. The revised composite flag system - based on ≥ 5.0 mmol/L of plasma lactate, > 32 mmol/L of glucose, or > 150 mmol/L of sodium - identified twice as many patients with spuriously elevated MCV as the vendor recommended MCHC flagging system. The associated positive predictive value of 31%, while lower than the vendor flagging system (62%), was considered adequate for implementation in our laboratory. CONCLUSIONS: We recommend reporting clinically significant corrected MCVs, based on sample pre-dilution with the Sysmex buffer, when the proposed composite metabolic flag is triggered.