RESUMO
RATIONALE: The manuscript aimed to show that an unmeasurable capillary C-reactive protein (CRP) should be a red flag that can indicate a possible severe hematological pathology. PATIENTS CONCERNS AND DIAGNOSES: The authors present 3 case reports of children with fever examined at the pediatric emergency department. Fever is among the most frequently exhibited symptoms of acute pediatric infectious diseases. However, sometimes fever can be the manifestation of other serious noninfectious diseases. CRP is a marker widely used in clinical pediatric practice to help us evaluate inflammation and possible bacterial infection. All mentioned patients had unmeasurable CRP from capillary blood, even though venous CRP ranged from 14 to 21 mg/L. All of the patients were consequently diagnosed with severe hemato-oncological disease. Possible explanations are that a change in blood viscosity or an elevation of circulating immune complexes in the blood of patients with leukemia leads to malfunctioning immunoturbidimetry measurement. LESSON: Although these findings are very interesting and could lead to faster recognition of acute leukemia in pediatric clinical practice, further prospective study is needed for their confirmation.