Billing and Clinical Guidelines for Surgical Microbiology Specimens

Introduction

Accurate diagnosis of surgical site infections and other deep-seated infections relies heavily on the quality and quantity of specimens submitted for microbiological analysis. Insufficient or improperly collected samples can lead to false-negative results, delayed diagnosis, and inappropriate treatment, ultimately impacting patient outcomes. Furthermore, understanding the billing implications and compliance with regulatory bodies like the Centers for Medicare & Medicaid Services (CMS) is crucial for clinical laboratories. This report synthesizes current recommendations from clinical guidelines, including those from the Clinical and Laboratory Standards Institute (CLSI) and the Infectious Diseases Society of America (IDSA), recent scientific literature regarding the optimal number of surgical/intraoperative tissue samples for microbiology testing, and relevant CMS billing policies.

1. CMS Billing Policies and Limitations

The Centers for Medicare & Medicaid Services (CMS) regulates the number of billable units through the National Correct Coding Initiative (NCCI) and Medically Unlikely Edits (MUEs).

Medically Unlikely Edits (MUE)

MUEs represent the maximum units of service (UOS) that a provider would typically report for a single beneficiary on a single date of service.

Key Definition:

• MAI 3 (Clinical): These are "per day" edits based on clinical benchmarks. Medicare may pay for services exceeding these values if an appeal is filed with documentation supporting medical necessity (e.g., multiple distinct surgical sites).

Billing Multiple Specimens

According to the NCCI Policy Manual (Chapter 10, Section K):

• Per Site Billing: Each distinct anatomical site requiring a separate culture setup is generally billable.
• Modifiers: Use Modifier 59 or XS (Separate Structure) to indicate that cultures were performed on different anatomical sites (e.g., Deep Tissue vs. Bone).
• Example: If three separate tissue specimens (Fascia, Muscle, Bone) are submitted from a single surgery, 87070 can be billed 3 times using the appropriate modifier.

2. General Principles of Specimen Collection

The Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM) emphasize that proper specimen selection, collection, and transport are critical for accurate microbiological diagnosis. While specific numbers of samples can vary based on the type of infection and anatomical site, several overarching principles apply:

• Sterility: Samples should be collected using sterile techniques to minimize contamination from commensal flora.
• Representativeness: Specimens should be obtained from the actual site of infection, ideally from the leading edge of infection or the most viable portion of the tissue.
• Adequate Quantity: Sufficient tissue volume is necessary to allow for various microbiological assays, including culture, microscopy, and molecular tests.
• Timely Transport: Specimens must be transported to the laboratory promptly and under appropriate conditions (e.g., anaerobic containers for anaerobic cultures, viral transport media for viruses) to maintain organism viability.

3. Clinical Recommendations (CLSI, IDSA, EBJIS)

Clinical guidelines often recommend a higher number of specimens than the standard MUE values to maximize diagnostic sensitivity, particularly for "culture-negative" or indolent infections.

Periprosthetic Joint Infection (PJI)

For suspected PJI, the consensus among major societies (IDSA, EBJIS, ICM) is to collect multiple specimens:

• Optimal Number: 5 to 6 distinct tissue specimens is considered the gold standard.
• Rationale: Collecting fewer than 5 specimens significantly reduces the sensitivity for detecting low-virulence organisms (e.g., Cutibacterium acnes, Coagulase-negative Staphylococci).
• Procedure: Each specimen should be collected using separate sterile instruments to avoid cross-contamination.

Fracture-Related Infection (FRI)

FRI diagnosis also benefits from standardized and adequate tissue sampling during surgical debridement.

• Optimal Number: Hellebrekers et al. (2019) recommend that standardized intraoperative sampling for FRI should consist of at least five (≥5) deep tissue samples, each obtained with sterile instruments. Dudareva et al. (2021) also investigated the accuracy of different numbers of specimens for microbiological testing in suspected FRI.
• Rationale: Similar to PJI, collecting multiple deep tissue samples from different areas of the infected site is crucial for maximizing the detection rate of pathogens in FRI, which can often be polymicrobial and involve biofilm formation.

General Surgical Site Infections (SSI) and Other Deep Tissue Infections

For other surgical site infections or deep tissue infections where specific guidelines like those for PJI or FRI may not exist, general principles of multiple sampling still apply.

• General Recommendation: The IDSA/ASM guide (Miller et al., 2018) generally recommends submitting multiple tissue specimens for aerobic and anaerobic cultures. Specifically, they suggest four samples if using conventional plate and broth cultures, and three if culturing tissues in aerobic and anaerobic blood culture bottles. Gandhi et al. (2017) also support a minimum of four tissue cultures from representative areas to maximize pathogen identification.
• Limits: While increasing the number of samples generally improves yield, there can be practical limits related to surgical time, tissue availability, and cost. The key is to balance diagnostic yield with clinical feasibility. The literature suggests that beyond 4–6 samples, the incremental diagnostic benefit often diminishes.

4. Recent Clinical Studies and Findings (2023–2025)

Recent literature reinforces the "Rule of Five" and explores new methodologies to improve yield.

The "Rule of Five" Validation

A 2024 systematic review confirmed that the EBJIS criteria (requiring 5 specimens) provide the highest sensitivity (up to 95%) compared to the older MSIS or IDSA criteria.

• Finding: Diagnostic accuracy was modeled using 2, 3, or 4 specimens; all were inferior to the standard 5-specimen protocol.

Histopathology Correlation

A 2025 study in The Bone & Joint Journal suggested that 3 to 6 tissue specimens for histopathological analysis are most cost-effective, providing a balance between diagnostic yield and laboratory resources.

5. Role of CLSI Guidelines

While specific CLSI documents directly dictating the number of surgical samples for microbiology are not as explicit as some disease-specific guidelines, CLSI provides foundational standards for specimen collection, transport, and processing that underpin all microbiological testing. Documents such as CLSI M22 (Quality Control for Commercially Prepared Microbiological Culture Media) and CLSI M52 (Verification of Commercial Microbial Identification and Antimicrobial Susceptibility Testing Systems) focus on laboratory procedures and quality control rather than the quantity of clinical samples. CLSI M47 (Blood Cultures) recommends 2 to 3 sets of blood cultures per septic episode, which aligns with the need for multiple samples to distinguish pathogens from contaminants.

6. Practical Recommendations for Lab Directors

To align clinical best practices with billing compliance, consider the following operational strategies:

1. Standardize Collection Kits: Create surgical "PJI Kits" that include 5–6 pre-labeled containers to encourage surgeons to meet the clinical gold standard.
2. Documentation for MUE Overrides: Since MUE for 87070 is 3 (Practitioner), billing 5 units will trigger a denial. Ensure the pathology report explicitly names 5 distinct anatomical sites (e.g., "Anterior Pseudocapsule," "Posterior Acetabular Tissue") to facilitate successful appeals for medical necessity.
3. Reflex Testing Logic: Set up lab protocols to automatically perform identification (87077) and susceptibility (87186) on each unique isolate across all specimens.
4. Audit Defense: Maintain a "Medical Necessity Policy" for the lab that cites the EBJIS and IDSA guidelines to justify the routine collection of 5+ specimens in surgical cases.

Summary Table of Recommendations

Conclusion

The comprehensive approach to surgical microbiology specimen collection and testing must integrate both clinical best practices and billing compliance. While clinical guidelines consistently advocate for the collection of multiple (typically 3–6) distinct tissue samples to maximize diagnostic yield, particularly for challenging infections like PJI and FRI, laboratories must also navigate CMS billing policies. Strategic documentation, use of appropriate modifiers, and clear internal policies are essential to justify the medical necessity of extensive sampling and ensure proper reimbursement. Adherence to these integrated recommendations is paramount for accurate diagnosis, effective patient management, and laboratory operational efficiency.

References

1. Peel, T. N., et al. (2017). Optimal Periprosthetic Tissue Specimen Number for Diagnosis of Prosthetic Joint Infection. Journal of Clinical Microbiology, 55(1), 234–243. Link
2. Hellebrekers, P., et al. (2019). Getting it right first time: The importance of a structured tissue sampling protocol for diagnosing fracture-related infections. Injury, 50(10), 1735–1739. Link
3. Miller, J. M., et al. (2018). A Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2018 Update by the IDSA and ASM. Clinical Infectious Diseases, 67(6), e1–e94. Link
4. Rottman, M., et al. (2025). 2025 ICM: Sample Collection and Agent Identification. The Journal of Arthroplasty, 41(1, Supplement 1). Link
5. Kim, S. J., et al. (2021). Current Guideline for Diagnosis of Periprosthetic Joint Infection. Hip & Pelvis, 33(1), 11–18. Link
6. Dudareva, M., et al. (2021). Providing an Evidence-Base for Tissue Sampling and Culture Interpretation in Suspected Fracture-Related Infection. Bone & Joint Research, 10(9), 578–586. Link
7. Gandhi, R., et al. (2017). How Many Cultures Are Necessary to Identify Pathogens in Periprosthetic Joint Infection? The Journal of Arthroplasty, 32(10), 3186–3189. Link
8. Osmon, D. R., et al. (2013). Diagnosis and Management of Prosthetic Joint Infection: Clinical Practice Guidelines by the IDSA. Clin Infect Dis. Link
9. McNally, M., et al. (2021). The EBJIS definition of periprosthetic joint infection: a practical guide for clinicians. Bone Joint J. Link
10. CLSI M47 (Blood Cultures). Link
11. Watanabe, S., et al. (2024). Differences in diagnostic sensitivity of cultures between sample types in PJI: a systematic review. J Arthroplasty. Link
12. Three to six tissue specimens for histopathological analysis are most effective. Bone Joint J. 2025. Link
13. CMS. Medicare NCCI Policy Manual, Chapter 10. Effective Jan 1, 2025. Link