Related Experiment Video
Updated: Dec 15, 2025
Author Spotlight: Advancing Lung Transplant Immunology Through Intravital Imaging
Published on: April 19, 2024
The impact of C4d testing on tissue adequacy in lung transplant surveillance
Sarah Hackman1, Gabriela Gonzalez1, Cynthia A Forker1
1UT Health San Antonio, Department of Pathology, Mail Code 7750, 7703 Floyd Curl Drive, San Antonio, TX 78229, United States of America.
Insights
Withholding tissue for C4d testing in lung transplant biopsies reduces adequate specimen size. This impacts 21% of samples, raising questions about C4d utility in marginal cases.
Area of Science:
- Transplantation immunology
- Pulmonary pathology
- Diagnostic pathology
Background:
- Surveillance transbronchial biopsies are crucial for diagnosing lung allograft rejection.
- Established criteria exist for acute cellular rejection, but antibody-mediated rejection (AMR) findings are variable.
- C4d immunofluorescence testing can enhance AMR detection but requires biopsy tissue.
Purpose of the Study:
- To evaluate the impact of C4d testing on the adequacy of surveillance transbronchial lung biopsy specimens.
- To determine the frequency of marginal biopsy samples affected by tissue allocation for C4d testing.
Main Methods:
- Retrospective review of 1400 surveillance transbronchial lung biopsies (2008-2017).
- Assessed adequacy based on a standard of five pieces of well-expanded alveolar parenchyma.
- Categorized samples as adequate (≥5 pieces), marginal (4 pieces), or inadequate (≤3 pieces).
Main Results:
- 653 out of 1400 biopsies (47%) met the adequacy criteria of ≥5 pieces.
- 747 biopsies had <5 pieces; 290 of these were classified as marginal.
- In all marginal cases, tissue was withheld for C4d immunofluorescence testing.
Conclusions:
- Withholding tissue for C4d testing reduces the proportion of adequate specimens by approximately 21%.
- Over 10 years, 290 marginal cases were identified where C4d testing impacted specimen adequacy.
- The utility of C4d testing in marginal surveillance transbronchial biopsies warrants careful consideration due to its impact on sample size.
Background:
Surveillance transbronchial biopsies are routinely used to assess lung allograft rejection. While the criteria for diagnosing acute cellular rejection have been well-established, the morphological findings associated with antibody mediated rejection are variable. To increase the sensitivity for antibody mediated rejection, a portion of a biopsy can be used for C4d immunofluorescence testing, along with histologic findings and donor specific antibodies. When the number of alveolar pieces in a biopsy is small, the relative utility of sending one piece for C4d testing is unclear.
Methods:
Pathology reports of 1400 surveillance transbronchial lung biopsies from 2008 to 2017 were reviewed to obtain the number of pieces of alveolar parenchyma in each case. Based on a standard definition of adequacy as five pieces of well-expanded alveolar parenchyma, reports with five fragments were grouped as "adequate", four pieces as a "marginal" sample, and three or less were considered an "inadequate" sample.
Results:
Of the 1400 biopsies, 653 specimens had 5 or more pieces of alveolar parenchyma.747 specimens were submitted with less than 5 pieces and 290 of those were considered marginal. In all marginal cases, a piece was withheld for C4d immunofluorescence testing.
Conclusions:
About 21% of specimens would have the recommended 5 pieces of alveolar parenchyma if not for the withholding of pieces for C4d IF testing. Over the span of 10 years, 290 such cases were recorded at our institution. Given this nontrivial impact, it is unclear if C4d immunofluorescence testing should be performed on surveillance transbronchial biopsies when the number of pieces in the specimen is marginal.
