Electrolytes in sick neonates - which sodium is the right answer?

Area of Science:

• Clinical Chemistry
• Neonatal Medicine
• Analytical Chemistry

Background:

• Hypoproteinaemia can lead to falsely elevated sodium readings with indirect ion-selective electrode (ISE) methods used in main laboratory analyzers.
• This contrasts with direct ISE methods used in point-of-care testing (POCT) analyzers.
• Neonatal intensive care unit (NICU) samples are particularly susceptible to these measurement discrepancies.

Purpose of the Study:

• To investigate the prevalence of hypoalbuminaemia in NICU samples.
• To determine the impact of hypoalbuminaemia on sodium measurements obtained from both POCT and main laboratory analyzers.
• To assess the clinical implications of these measurement differences on electrolyte status classification.

Main Methods:

• Retrospective analysis of paired neonatal blood samples.
• Comparison of sodium measurements obtained from a main laboratory analyzer and a neonatal unit blood-gas (POCT) analyzer.
• Statistical analysis to correlate albumin levels with sodium measurement differences.

Main Results:

• Hypoalbuminaemia (<30 g/l) was identified in 1400 out of 2420 (57.9%) paired samples.
• Laboratory analyzer consistently reported higher sodium values than POCT, with the difference increasing as albumin levels decreased.
• A significant sodium difference (>3 mmol/l) occurred in 31% of samples, leading to misclassification of hyponatraemia (9.4% underestimation) and hypernatraemia (3.8% overestimation).

Conclusions:

• Hypoalbuminaemia is a common finding in critically ill neonates.
• Routine electrolyte monitoring using standard laboratory and POCT analyzers can yield significantly different sodium results in this population.
• Direct ISE measurement, as employed in blood-gas analyzers, may provide more accurate electrolyte assessment in neonates with hypoalbuminaemia.