Electrolytes in sick neonates - which sodium is the right answer?
BACKGROUND
Hypoproteinaemia leads to spuriously high-sodium values when measured by indirect ion-selective electrodes (ISE) as used in main laboratory analysers compared with direct ISE employed in point-of-care analysers (POCT). The authors, therefore, investigated the occurrence of hypoalbuminaemia and its effect on measured sodium from POCT and the main laboratory analyser of neonatal intensive-care samples.


METHODS
Sodium, in paired retrospective samples, measured by the main laboratory and neonatal unit blood-gas (POCT) analysers were compared.


RESULTS
Hypoalbuminaemia (<30 g/l) was present in 1400/2420 paired results. Sodium was higher when measured by laboratory analyser, the difference increased with decreasing albumin; sodium (laboratory - POCT)=7.6 (±1.1)-0.22 (±0.04)×albumin. A difference >3 mmol/l was present in 31% and consequently underestimated (9.4%) hyponatraemia and overestimated (3.8%) hypernatraemia.


CONCLUSIONS
Hypoalbuminaemia is common in sick neonates and monitoring electrolytes using POCT and laboratory analysers frequently yield significantly different results with consequent misclassification. In these patients, measurement of electrolytes by direct ISE (blood-gas analyser) may be more accurate.
Clinical Biochemistry Unit, Canterbury Health Laboratories, Cnr Hagley Ave and Tuam Street, PO Box 151, Christchurch 8011, New Zealand. richard.king@cdhb.govt.nz
Richard I
RI
King
Richard J
RJ
Mackay
Christopher M
CM
Florkowski
Adrienne M
AM
Lynn
D001784:Blood Gas Analysis; D002196:Capillaries / Q000502:physiology; D004573:Electrolytes / Q000097:blood*; D006801:Humans; D034141:Hypoalbuminemia / Q000453:epidemiology*; D007231:Infant, Newborn; D017736:Ion-Selective Electrodes; D019095:Point-of-Care Systems; D012964:Sodium / Q000097:blood
D004573:Electrolytes; D012964:Sodium