SERUM IONIZED CALCIUM, SERUM AND INTRACELLULAR PHOSPHATE, AND SERUM PARATHORMONE CONCENTRATIONS IN ACUTE MALARIA

Previous studies have shown depressed serum corrected calcium and phosphate concentrations in acute falciparum malaria. To characterize malaria-associated disturbances in mineral homoeostasis further, serum ionized calcium and intracellular phosphate were measured in 18 patients (10 with falciparum malaria, 8 with vivax malaria) and 10 healthy controls. Six patients (4 falciparum, 2 vivax) had admission serum ionized calcium concentrations below the absolute control range (< 1.15 mmol/litre) and a further six (3 falciparum, 3 vivax) developed ionized hypocalcaemia during treatment. The patients with falciparum malaria had the lowest values at presentation (median [95% confidence intervals in brackets]: 1.17 [1.12-1.23] vs. 1.20 [1.18-1.24] mmol/litre in controls, P=0.035) in the presence of depressed simultaneous serum parathormone concentrations (1.2 [0.6-1.9] vs. 1.6 [1.1-2.6] pmol/litre; P=0.05). Admission serum phosphate concentrations were lower in the malaria patients (P=0.007 vs. controls), especially in those with falciparum malaria (0.85 [0.7-1.1] vs. 1.2 [1.1-1.3] mmol/litre in controls; P=0.002); patients with falciparum malaria also had significantly lower intracellular phosphate than controls (0.74 [0.58-0.90] vs. 0.88 [0.66-1.04] mmol/litre red cells; P=0.047). There was a weak association between serum corrected and ionized calcium in the malaria patients (r(s)=0.31,n=18,P>0.1), but serum and intracellular phosphate correlated significantly (r(s)=0.71,n=17,P<0.001) with a regression line slope of 0.49 and intercept of 0.27 mmol/litre of red cells. These results confirmed that mild ionized hypocalcaemia in the presence of a depressed parathormone response is common in acute malaria; although the serum phosphate may also be low, intracellular phosphate does not necessarily fall by an equivalent amount.