procalcitonin ( pct ) is elevated in serum of patients with severe infections of bacterial or parasitic origin . increased levels it has been recently demonstrated that pct levels in falciparum malaria correlate with parasitemia and disease severity , and that markedly elevated values ( > 25 ng / ml ) are associated with a high risk of fatal outcome . in this study , pct levels were investigated in patients with tertian malaria , which is generally mild without severe organ complications and which is usually non - fatal . patients with malaria who are seen at the site of the study follow a standard protocol for prospective assessment of relevant parameters . thirty seven unselected , consecutive patients with tertian malaria due to plasmodium vivax or plasmodium ovale seen during 2000 and 2001 and in whom all necessary data were available , were analysed . concomitant infections with a possible impact on pct levels were excluded by history , clinical examination , and laboratory tests . patients who were raised in an area endemic for tertian malaria were defined as semi - immune ( n = 12 ) . blood samples were drawn immediately before treatment ( day 0 ) and on follow - up until day 7 . pct serum levels were determined using an immuno - luminometric assay ( lumitest pct , brahms diagnostica gmbh , berlin , germany ) according to the manufacturer 's specifications . routine laboratory investigations included differential blood count , haemoglobin , platelets , standard coagulation tests , creatinine , neopterin , c - reactive protein , lactate dehydrogenase and liver function tests . patients were monitored by physical examination , ecg , abdominal ultrasound , and chest radiography . two patients , in whom the plasmodium species could not be differentiated by the first blood sample , received mefloquine . results were compared with data obtained at the same site in a cohort of plasmodium falciparum patients and published earlier . all patients had a low or modest parasitemia ( < 1% ) , haemoglobin concentrations > 12 g / dl ( except two patients with 8.4 and 10.7 g / dl ) , normal renal and liver function , and no signs of concomitant infections . the disease progression was always mild with a rapid parasite clearance in response to anti - malarial treatment . initial pct concentrations varied between < 0.1 ng / ml and 47 ng / ml and , in all patients , dropped with declining parasite counts and clinical recovery ( figure 1 ) . pct levels before treatment did not correlate with parasite burden , laboratory values , reported duration of illness , body temperature or fever attacks , or the presence of semi - immunity . before treatment , two thirds of the patients showed normal ( < 0.5 ng / ml ) or slightly elevated pct levels ( geometric mean 0.44 ng / ml , range < 0.1  2.1 ) . in a subset of patients ( 12/37 ) , however , pct was markedly elevated ( geometric mean 14.4 ng / ml ; range 4.8  47 ) . pct in these patients was in the range of patients with severe and complicated falciparum malaria ( > 2.5 ng / ml , figure 2 ) . the two groups with low or high pct were undistinguishable by means of history , clinical signs , or laboratory parameters . serum procalcitonin ( pct ) concentrations in 37 patients with tertian malaria immediately before treatment ( day 0 ) , and on follow - up . box : median , 25 , and 75percentile ; whiskers : 5and 95percentile ; star : 1and 99percentile ; open squares : mean ; filled circles : geometric mean . pct levels before treatment in patients with tertian malaria ( triangles ) compared to falciparum malaria ( open squares : survivors ; filled squares : patients that died ) . cluster a : semi - immune patients ; cluster b : non - immune patients with mild disease ; cluster c : non - immune patients with severe and complicated disease . the horizontal line at 2.5 ng / ml is the lower cut - off for complicated falciparum malaria and arbitrarily discriminates a high level from a low level group in tertian malaria . in contrast to falciparum malaria and other infectious diseases in which pct is induced , markedly elevated pct levels could be observed in this cohort in one third of the patients without any correlation to disease severity . this could not be attributed to concomitant infections or complications . while the study was not statistically powered to significantly detect weak correlations , although the pathophysiology of pct has not been determined yet , the question remains , what is so different in tertian malaria . in contrast to bacterial or other infectious diseases , tertian malaria is characterized by surges in parasitic density and fever every 48 hours , leaving time in - between for the defence system to recover . . it would be interesting to find out whether such host factors indicated an individual risk of developing severe falciparum malaria . the unique feature of pct induction in tertian malaria raises interesting questions about the clinical and pathophysiological role of pct in infectious diseases and in malaria in particular . ss assessed the clinical parameters and participated in the design of the study and the statistical analysis .