National Reference Laboratory for Toxoplasmosis, National Institute of Public Health, Prague, Czech Republic.
National Institute of Public Health, Unit of Biostatistics, Prague, Czech Republic.
PLoS One. 2023 Apr 13;18(4):e0284499. doi: 10.1371/journal.pone.0284499. eCollection 2023.
For the proper diagnosis of toxoplasmosis it is essential to determine the stage of the infection, for which the most preferred method is IgG avidity test. The avidity index (AI) should initially be low (AI≤0.3) in the acute phase and increase during the infection. However, persistent low avidity can occur in patients with latent toxoplasmosis, which can complicate the interpretation of the results. The aim of the study is to explain the causes of this phenomenon.
A retrospective study was carried out with 717 serum samples collected from 442 patients from the categories of pregnant and non-pregnant women, men, and newborns + infants (age < 0.5 year). The trends of AI kinetics were evaluated in repeatedly examined patients. The frequency of cases with low avidity was compared in individual categories of patients and in groups of people with acute and non-acute toxoplasmosis.
The proportion of patients with initially low avidity was 42.1% in the acute toxoplasmosis group while it was 13.0% in the non-acute groups. In uninfected newborns with anti-Toxoplasma antibodies transmitted from the mother, a decrease in IgG avidity levels over time was observed, resulting in 29.2% of samples showing low (improper) avidity. While the dynamics of IgG avidity and the frequency of cases of improperly low avidity were similar in men and pregnant and non-pregnant women, the category of newborns and infants differed substantially for these indicators.
Due to acceptable specificity and negative predictive value, high avidity can rule out acute toxoplasmosis, but moderate sensitivity complicates the possibility of its confirmation. The results of the avidity test must be interpreted in the context of the results of other methods.
为了正确诊断弓形体病，确定感染阶段至关重要，而 IgG 亲和力试验是最优选的方法。亲和力指数（AI）在急性阶段初始时应较低（AI≤0.3），并在感染过程中增加。然而，潜伏性弓形体病患者可能会出现持续的低亲和力，这可能会使结果的解释复杂化。本研究旨在解释这种现象的原因。
对 442 名孕妇和非孕妇、男性以及新生儿+婴儿（年龄<0.5 岁）患者的 717 份血清样本进行了回顾性研究。评估了反复检查患者的 AI 动力学趋势。比较了急性和非急性弓形体病患者各亚组和人群中低亲和力的病例频率。
急性弓形体病组中初始低亲和力患者的比例为 42.1%，而非急性组为 13.0%。在由母亲传播抗弓形抗体的未感染新生儿中，IgG 亲和力水平随时间降低，导致 29.2%的样本显示低（不当）亲和力。虽然 IgG 亲和力的动态和不当低亲和力病例的频率在男性以及孕妇和非孕妇中相似，但新生儿和婴儿的类别在这些指标上存在很大差异。
由于具有可接受的特异性和阴性预测值，高亲和力可以排除急性弓形体病，但中等敏感性使确认其感染的可能性复杂化。亲和力试验的结果必须结合其他方法的结果进行解释。
