Clinical Equivalence Of Heparinized Arterial Plasma To Venous Serum For Magnesium And Phosphate Measurement Among Patients Admitted At The Intensive Care Unit Of Moi Teaching And Referral Hos

ABSTRACT

Electrolytes routinely measured in patients in Intensive Care Unit (ICU) are sodium, potassium,

chloride, calcium, magnesium and phosphate. Of these; sodium, potassium, chloride and calcium

are measured as part of tests done during blood gas analysis (BGA) using arterial blood. However,

magnesium and phosphate are measured from a venous serum sample since they cannot be

measured during BGA. Both arterial and venous puncture are traumatizing to the patient and

trauma increases when both are done numerous times on the same patient in a single day. Plasma

obtained from sodium-heparin anticoagulant is yet to be used as a sample of choice for measuring

magnesium and phosphate since it is not clear whether there is clinical equivalence between

magnesium and phosphate concentrations obtained from venous serum and arterial plasma. It is

clinically important that those measurements should give equivalent results and confirm the

closeness to the absolute value. The main objective was to assess the equivalence of arterial and

venous blood magnesium and phosphate concentrations. The specific objectives were; to

determine the mean difference between magnesium concentration in arterial blood plasma and

venous blood serum, to determine the mean difference between phosphate concentration in arterial

blood plasma and venous blood serum, to determine the correlation between magnesium

concentration in arterial blood plasma and venous blood serum and to determine the correlation

between phosphate concentration in arterial blood plasma and venous blood serum. This study

used a cross-sectional research design and was carried out at Moi Teaching and Referral Hospital

(MTRH) where one hundred and fifty-three patients admitted at MTRH ICU underwent arterial

and venous puncture to obtain arterial and venous blood which was used for magnesium and

phosphate measurement on an automated chemistry laboratory analyzer. Mean difference between

magnesium concentration in plasma and serum calculated using paired t-test was 0.03(t=1.23)

p=0.22 while mean difference between phosphate concentration in plasma and serum was

0.14(t=1.18) p=0.24. Magnesium correlation between plasma and serum was r=0.98 [p = 0.00 (