MADRID – Thomsen-Friedenreich antigen activation is useful as a novel early predictor of empyema in pediatric community-acquired pneumonia, Chi-Jung Chang, MD, reported at the annual meeting of the European Society for Paediatric Infectious Diseases.
In her retrospective study of 142 Taiwanese children and adolescents hospitalized for community-acquired pneumonia (CAP), Thomsen-Friedenreich antigen (TA) activation had 100% specificity, 100% positive predictive value, and 31% sensitivity for Streptococcus pneumoniae as the causative microorganism.
Moreover, the higher the TA activation titer, the more severe the pneumonia complications that followed, according to Dr. Chang of MacKay Children’s Hospital in Taipei, Taiwan.
The value of this lab test lies in its speed and accuracy for detection of S. pneumoniae CAP. Conventional culture methods are relatively slow and have poor sensitivity, because a child often already has been on empiric antimicrobial therapy and the culture specimen is unwittingly obtained from a sterile site, she explained.
Twenty-two of the 142 children and adolescents hospitalized for lobar CAP were TA activation positive at admission. They were considerably sicker than were the 120 patients who were TA activation negative. Their initial C-reactive protein level was 31.9 mg/dL, twice that of the negative group. Their peak CRP during the hospital stay was significantly higher as well, as was their peak WBC.
Hospital lengths of stay were longer in the TA activation–positive group. Eighteen of 22 TA activation–positive patients (82%) were admitted to the ICU for an average of 8 days, compared with 9% of the negative group.
All TA activation–positive patients had complicated pneumonia with parapneumonic effusions, empyema, necrotizing pneumonia, and/or lung abscesses, as did 36% of the negative group.
S. pneumoniae was the most common pathogen in this study of CAP. It was the responsible microbe in all 22 of the TA activation–positive patients and in 29% of the TA activation–negative ones. The most common serotype in the TA activation group was 19A, which accounted for 12 of the 22 cases. This also was the predominant serotype found in CAP across all Taiwan during the first half of this decade, when the study took place.
In a multivariate logistic regression analysis, TA activation was far and away the strongest independent predictor of empyema, with an associated 15.8-fold increased risk. The other two independent predictors – longer fever duration prior to hospitalization and a higher initial CRP level – were far less robust, according to Dr. Chang.
How TA activation works as a predictor
TA is present on the surface of erythrocytes, platelets, and glomeruli, but ordinarily it is covered by a layer of N-acetylneuraminic acid. Streptococcus pneumoniae produces circulating neuraminidases, which cleave the N-acetylneuraminic acid and expose the underlying TA. The TA then quickly becomes activated through interaction with the anti-TA antibodies, which are normally present in plasma. Once activated, the TA stays so for weeks to months.
Other neuraminidase-producing microorganisms include Clostridium perfringens, Escherichia coli, and Bacteroides.
Dr. Chang and her colleagues used the peanut lectin agglutination method in their TA activation testing.
She reported having no financial conflicts regarding her study.