Capital Bluecross CRP and ESR Coverage Update | OpenPayer
CurrentCapital BluecrossPolicy AHS - G2155
General Inflammation Testing (CRP and ESR)
Defines coverage and limitations for measurement of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) for diagnosing and monitoring inflammatory conditions for Capital Bluecross members.
Policy Summary
PayerCapital Bluecross
PolicyGeneral Inflammation Testing (CRP and ESR)
Policy CodePolicy AHS - G2155
Change TypeNo material changes in this revision
Effective DateN/A
Next Review DateNov 1, 2025
Key ActionOrder CRP or ESR only for a diagnosed or suspected inflammatory condition; if both are ordered, only CRP will be approved.
No material clinical or coverage changes in this revision.
CoveredCovered when indicated
Not coveredESR not covered w/o diagnosis
CRP preferredCRP preferred when both ordered
3Procedure codes listed
every 2-3 daysAHO early monitoring
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Coverage Criteria
Covered indications (per Note 1 and condition table)
Measurement of CRP and/or ESR meets coverage criteria when specified conditions are present (Note 1).
Covered testing: Measurement of CRP and/or ESR meets coverage criteria for the conditions specified in Note 1.
Either conventional or high-sensitivity CRP testing are allowed; when either CRP or ESR are allowed, CRP is the preferred biomarker. If both CRP and ESR are ordered for a condition where one is allowed, only CRP will be approved.
Covered indications (examples): Includes but is not limited to: acute and chronic urticaria; acute hematogenous osteomyelitis (AHO); ankylosing spondylitis; arthritis; Castleman's disease; general inflammation; Hodgkin lymphoma; irritable bowel syndrome (to exclude IBD); large vessel vasculitis (GCA, Takayasu); polymyalgia rheumatica; periprosthetic joint infections (PJI); rheumatoid arthritis; systemic lupus erythematosus; T-cell lymphomas.
Test preference and suggested frequency are specified per condition in the policy table (e.g., CRP preferred for AHO; ESR preferred for Hodgkin lymphoma; CRP and ESR for PJI).
Not medically necessary / not covered
Not covered scenarios
Not covered uses: Measurement of ESR for individuals without a diagnosed inflammatory condition does not meet coverage criteria.
Not covered uses: Measurement of CRP and/or ESR during a general examination without abnormal findings does not meet coverage criteria.
Guideline-based condition-specific testing
Condition-specific coverage and monitoring practices described by specialty guidelines:
PMR and GCA initial testing: For polymyalgia rheumatica (PMR) obtain CRP and/or ESR as part of baseline laboratory workup prior to initiating long-term steroid therapy; monitor ESR or CRP (e.g., every 3 months during long-term steroid therapy). For giant cell arteritis (GCA) obtain CRP and ESR (or plasma viscosity) and full blood count at presentation and include CRP and/or ESR at follow-up visits as clinically indicated.ESR >30–40 mm/hr or elevated CRP often present in PMR
Sources: EULAR, BSR/BHPR
Rheumatoid arthritis and spondyloarthritis monitoring: Monitor disease activity using validated composite measures (which may incorporate CRP or ESR); frequency typically every 1–3 months while active, then less frequently once treatment target is achieved.every 1–3 months while active; 6–12 months when stable
Source: EULAR/ACR/NICE
Pediatric acute hematogenous osteomyelitis (AHO):
Guideline-based use and monitoring
Clinical and laboratory guidance informing use of CRP and ESR:
Preferred initial test: CRP is the preferred first-line test to support diagnosis of inflammatory or infectious conditions; there is no indication to order ESR when CRP is elevated.
British Columbia guidance and pediatric AHO guidance support CRP as preferred baseline and monitoring test.
ESR requisition requirement: Order ESR in outpatient settings only with a written indication on the requisition where required; many outpatient laboratories will perform only CRP if both tests are ordered because ESR may not be payable.
Operational limitation per Government of British Columbia guidance.
Pediatric AHO monitoring frequency: In confirmed pediatric acute hematogenous osteomyelitis obtain serum CRP on initial evaluation and monitor every 2–3 days during the early therapeutic course rather than daily, then weekly or periodically until normalization or a clear trend is evident.every 2–3 days early in course, then weekly
Measurement of C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR) meets coverage criteria when the tested individual has a diagnosed or suspected inflammatory condition as specified in the policy Note. For individuals without a diagnosed inflammatory condition, measurement of ESR does not meet coverage criteria. Likewise, measurement of CRP and/or ESR as part of a routine general examination without abnormal findings does not meet coverage criteria.
The American Society for Clinical Pathology (Choosing Wisely) advises not to order ESR to look for inflammation in patients with undiagnosed conditions. Instead, order CRP to detect acute-phase inflammation because CRP typically rises earlier and normalizes faster than ESR and has higher sensitivity and specificity for acute inflammation.
The American Gastroenterological Association (2019) suggests against using ESR or CRP to screen for inflammatory bowel disease (IBD) in patients presenting with chronic diarrhea (conditional recommendation, low-quality evidence). The AGA notes limited settings where CRP may be reasonable (for example, when fecal markers are unavailable), but routine use for IBD screening is discouraged.
British Columbia guidance states that CRP is the preferred first test to support diagnosis of inflammatory or infectious conditions and there is no indication for ordering ESR when CRP is elevated. The BC outpatient payment schedule further specifies that ESR will be performed only if a written indication is provided on the requisition, and when both CRP and ESR are ordered most outpatient laboratories will only perform CRP because ESR may not be payable.
Assessment of CRP in asymptomatic individuals is indicated only for cardiovascular risk stratification using high-sensitivity CRP (hsCRP) when specifically requested. If hsCRP is desired for CV risk assessment it must be explicitly requested on the laboratory requisition.
Ordering ESR for individuals without a diagnosed inflammatory condition will be denied as not meeting coverage criteria. Similarly, ordering CRP and/or ESR as part of a routine general examination without abnormal findings will not meet coverage criteria and is excluded from coverage.
Routine use of ESR or CRP to screen for IBD is generally discouraged. The AGA recommends against routine screening with these blood tests for most patients presenting with chronic diarrhea, reserving CRP for select situations (for example when fecal testing is unavailable).
Repeat CRP testing should be guided by clinical status; routine repeat CRP testing for most infections without a change in clinical status is not indicated. For pediatric acute hematogenous osteomyelitis (AHO), guidelines recommend obtaining serum CRP at initial evaluation as a baseline and serial CRP monitoring every 2–3 days during early therapy, then weekly or periodic until normalization, while ESR is no longer routinely used to establish the diagnosis in children.
Covered Indications and Condition-Specific Details
Various inflammatory conditions including but not limited to acute and chronic urticaria, acute hematogenous osteomyelitis, ankylosing spondylitis, arthritis, Castleman's disease, general inflammation, Hodgkin lymphoma, IBS (to exclude IBD), large vessel vasculitis (GCA, Takayasu), polymyalgia rheumatica, periprosthetic joint infections, rheumatoid arthritis, systemic lupus erythematosus, T-cell lymphomas.
Covered indications and test preferences for a range of inflammatory conditions (examples):
Various inflammatory conditions: Acute and chronic urticaria (CRP or ESR); acute hematogenous osteomyelitis (CRP; serial monitoring recommended); ankylosing spondylitis (CRP or ESR); arthritis (CRP and ESR; monitoring 1–3 months initially); Castleman's disease (CRP); general inflammation (CRP); Hodgkin lymphoma (ESR; defined follow-up schedule); IBS to exclude IBD (CRP and ESR during initial assessment); large vessel vasculitis including GCA and Takayasu (CRP and ESR for diagnosis and monitoring); polymyalgia rheumatica (CRP or ESR at diagnosis and periodic monitoring); periprosthetic joint infections (CRP and ESR as adjuncts); rheumatoid arthritis (CRP or ESR for baseline and monitoring); systemic lupus erythematosus (CRP or ESR at assessment and during active disease); T-cell lymphomas (ESR).See condition-specific frequency recommendations in policy table
Test preference and frequency specified per condition in the policy Notes table.
Operational preference:
Provider Actions, Documentation & Billing Notes
Billing Rule
Requisition / Payment Requirement
Requisition / Payment requirement — follow local lab payment rules. Some outpatient laboratories (e.g., British Columbia guidance) will perform ESR only if a written indication is provided on the requisition and, when both CRP and ESR are ordered together, most outpatient labs will only perform and pay for CRP. Providers should document any required written indication on the requisition to ensure ESR will be processed and reimbursed.
Applicable codes: CPT 85651, 85652 (ESR) — may require written indication for performance/payment
When both CRP and ESR are ordered, many outpatient labs will perform only CRP (payable)
Note
WHO: CRP Preferred Over ESR
WHO preference — when choosing an inflammation biomarker, the World Health Organization recommends CRP (by EIA, RDT, latex agglutination or immunoassay formats) over ESR as the essential diagnostic tool for detecting inflammation. Use CRP as the preferred first test except in situations where ESR is specifically indicated by guideline or clinical need.
Coding and Procedure Codes
Applicable CPT/HCPCS Procedure CodesCPT
85651
Sedimentation rate, erythrocyte; non-automated.
85652
Sedimentation rate, erythrocyte; automated.
86140
C-reactive protein.
86141
C-reactive protein; high sensitivity (hsCRP).
PJI MSIS standard cutoffs (and study findings)
MSIS standard cutoffsESR 30 mm/h; CRP 10 mg/L (MSIS standard).
Study-suggested lower cutoffsStudy found ESR 10 mm/h and CRP 5 mg/L achieved ≥95% sensitivity (Bingham et al.).
ImplicationAccepted MSIS thresholds (ESR 30, CRP 10) have lower sensitivity and may produce false negatives; consider clinical context.
Neonatal early-onset sepsis CRP cutoff
Neonatal early-onset sepsis CRP cutoffCRP ≥10 mg/L used as cutoff in the cited retrospective cohort (Dhudasia et al., 2022).
CRP and/or ESR — varies by condition (selected examples)
Rheumatoid arthritis monitoringFrequency: 1–3 months initially, then 6–12 months once stable; Test preference: CRP or ESR.
Acute hematogenous osteomyelitis (AHO)CRP preferred; frequency: to confirm diagnosis, then every 2–3 days during early therapy and weekly until normalization.
Polymyalgia rheumaticaTest preference: CRP or ESR; frequency: at initial diagnosis and every 3 months during long-term steroid therapy.
CRP and/or ESR — monitoring every 1-3 months while active then less frequently
Active disease monitoring intervalMonitor disease activity every 1–3 months while disease active; less frequent (e.g., every 6–12 months) once treatment target achieved.
RA/early arthritis context
Ordering Requirements
Note
Order requirement — diagnosed/suspected inflammatory condition; CRP preferred
Order must be for a diagnosed or suspected inflammatory condition; when both CRP and ESR are ordered only CRP will be approved per policy Note 1.
Note
Ordering context — baseline and monitoring in rheumatologic care
CRP/ESR testing is used as part of baseline and monitoring assessments in rheumatologic care and is typically ordered by the primary clinician or relevant specialty managing the condition.
Billing Rule
Ordering limitation — ESR may require written requisition indication (BC)
Some outpatient laboratories may only perform CRP as the payable test; ESR may require a written indication on the requisition per British Columbia guidance.
Note
Not Covered
Measurement of ESR for individuals without a diagnosed inflammatory condition and measurement of CRP and/or ESR during a general exam without abnormal findings are explicitly listed as not covered uses under the policy.
ESR has limited utility as a screening test to predict rheumatoid arthritis or other connective tissue diseases; studies show low positive predictive values (for example, ESR predicted CTD in 35% and RA in 17% of cases in one review), indicating questionable clinical utility for ESR as a population screening test.
Routine CRP testing for early-onset neonatal sepsis is not supported by the cited retrospective cohort. In that study using a CRP cutoff of ≥10 mg/L, routine CRP testing did not improve time to detection or in-hospital mortality and was associated with increased evaluation and antibiotic use; the authors concluded diagnostic performance was insufficient to warrant routine testing.
Routine or population-level use of ESR or CRP to screen for inflammatory bowel disease is generally discouraged. The AGA guideline specifically recommends against using ESR or CRP to screen for IBD in most patients presenting with chronic diarrhea.
Routine repeat CRP testing for most infections without a documented change in clinical status is not indicated. Additionally, British Columbia guidance indicates that ESR ordered in outpatient settings may require a written indication on the requisition and may not be performed or paid unless that indication is provided; ordering ESR without the required written indication therefore risks non-performance or nonpayment.
Definitions
CRP definition — conventional and high-sensitivity CRP described
Conventional CRPCRP is an acute phase reactant produced by hepatocytes that can increase >1000-fold during acute inflammation; useful to monitor inflammatory response.
Assay formatsCRP can be assayed by rapid diagnostic tests, latex agglutination, immunoassay, and enzymatic immunoassays; units and methods vary between labs.
Role in monitoringWHO and other sources note CRP is preferred to detect inflammation and to monitor treatment response except in select conditions.
ESR definition — Westergren and alternate methods described
Westergren ESR methodThe Westergren method measures the distance blood settles in one hour and is the ICSH-referenced standard method.
Alternate/automated methods
Background
CRP and ESR are acute phase reactants used to detect and monitor systemic inflammation. CRP is produced by hepatocytes and typically rises rapidly during acute inflammation, while ESR measures the rate at which erythrocytes settle over one hour and is influenced by assay method, sample preparation, and noninflammatory factors. Both tests are used as nonspecific markers in a range of conditions including rheumatologic diseases, infections, and hematologic malignancies.
Policy Summary
PayerCapital Bluecross
PolicyGeneral Inflammation Testing (CRP and ESR)
Policy CodePolicy AHS - G2155
Change TypeNo material changes in this revision
Effective DateN/A
Next Review DateNov 1, 2025
Key ActionOrder CRP or ESR only for a diagnosed or suspected inflammatory condition; if both are ordered, only CRP will be approved.
Obtain serum CRP on initial evaluation as a baseline for monitoring; ESR is not routinely recommended for diagnosis in children. Repeat CRP every 2–3 days during the early therapeutic course, then weekly or periodic until normalization or clear trend toward normalization.
Periprosthetic joint infection (PJI): ESR and CRP are supported as adjunctive preoperative diagnostic tests for PJI but are not definitive alone; interpret results cautiously and in conjunction with clinical and microbiologic data.MSIS/AAOS supportive criteria (ESR and CRP used as minor criteria)
Source: AAOS; meta-analysis evidence cited
Hodgkin lymphoma staging and follow-up: ESR is listed as essential in adult Hodgkin Lymphoma workup per NCCN and should be tested within six months of diagnosis; elevated ESR at diagnosis should be recorded and included in follow-up laboratory studies per NCCN timeline.Use ESR to distinguish ESR <50 vs ≥50 for risk classification
Source: NCCN
IBD / IBS assessment: CRP (and ESR) may be used as adjuncts to clinical and endoscopic findings when evaluating for inflammatory bowel disease; a normal CRP alone should not be used to exclude IBD.
Source: literature summarized in policy and AGA guidance
When both CRP and ESR are allowed for a covered condition, CRP is preferred and will be approved if both are ordered; ESR-only testing without a diagnosed inflammatory condition is not covered.
Policy Note 1 and Government of British Columbia operational guidance support this preference.
Adjunctive use in preoperative and diagnostic evaluation for prosthetic joint infection:
PJI adjunctive testing: ESR and CRP are supported as adjunctive preoperative diagnostic tests for periprosthetic joint infection (PJI). They should be used in conjunction with clinical assessment and microbiologic testing and not as standalone diagnostic tests.MSIS/AAOS supporting criteria
CRP generally demonstrates higher diagnostic odds ratio than ESR; interpret results cautiously, especially for low-virulence organisms.
Hodgkin Lymphoma staging and follow-up
Hodgkin Lymphoma staging and follow-up considerations:
Hodgkin lymphoma workup: ESR is listed as essential in adult Hodgkin Lymphoma workup per NCCN and should be tested within six months of diagnosis; elevated ESR at diagnosis should be recorded and included in follow-up laboratory studies according to the NCCN follow-up schedule.Use ESR to classify risk (ESR <50 vs ≥50)
ESR level informs staging/risk and can affect treatment decisions such as radiation dosing.
Polymyalgia rheumatica (PMR) baseline and monitoring
PMR baseline and monitoring recommendations:
PMR baseline testing: At initial diagnosis of polymyalgia rheumatica obtain baseline laboratory workup including CRP and/or ESR to exclude mimics and establish a monitoring baseline prior to initiating therapy.
EULAR/BSR guidance support baseline acute phase reactant testing.
PMR monitoring during therapy: During long-term steroid therapy monitor ESR or CRP approximately every 3 months (frequency may vary based on clinical course).every 3 months during long-term steroid therapy
Source: BSR/BSR-BHPR and EULAR recommendations.
Inflammatory bowel disease adjunct assessment
Use of CRP/ESR in assessment for inflammatory bowel disease (IBD):
IBD adjunct assessment: CRP is used as an adjunct to clinical and endoscopic findings when evaluating for IBD; a normal CRP alone should not be used to exclude IBD.
AGA guidance and policy discussion note limited sensitivity and specificity of CRP for IBD.
Diagnosis and monitoring of giant cell arteritis (GCA) and polymyalgia rheumatica (PMR)
Diagnosis and monitoring for giant cell arteritis (GCA) and related recommendations:
GCA diagnostic testing: When starting glucocorticoids for suspected GCA, document diagnostic-relevant symptoms and obtain blood for full blood count, CRP and ESR before or immediately after commencing high-dose glucocorticoids.
If GCA is strongly suspected, the first steroid dose may be given without waiting for laboratory results (BSR guidance).
GCA follow-up monitoring: At follow-up visits include clinical assessment and measurement of at least full blood count and CRP and/or ESR as part of monitoring; increases in inflammatory markers alone should prompt clinical observation and may warrant closer clinical or radiographic assessment rather than automatic escalation of immunosuppression.
AHO baseline and monitoring: In children with suspected AHO perform serum CRP on initial evaluation as a baseline for sequential monitoring; ESR is no longer routinely used to diagnose pediatric AHO.
Repeat CRP every 2–3 days during early therapy, then weekly or until normalization per Pediatric ID Society/IDSA guideline.
Preoperative assessment for prosthetic joint infection
Preoperative assessment considerations for prosthetic joint infection (PJI):
Preoperative PJI assessment: Use ESR and CRP as adjunctive preoperative laboratory tests when evaluating for prosthetic joint infection; they should not be used in isolation to make the diagnosis.MSIS/AAOS supportive criteria
Strong evidence supports their adjunctive role; interpret with clinical and microbiologic data.
Suspected inflammatory or infectious conditions (general) and pediatric AHO baseline/monitoring
General suspected inflammatory or infectious conditions and pediatric AHO monitoring:
Preferred first-line testing: For suspected inflammatory or infectious conditions CRP is the preferred first-line test; high-sensitivity CRP (hsCRP) is reserved for cardiovascular risk stratification when specifically requested.
Government of British Columbia guidance and policy Note 1 support CRP preference.
AHO monitoring summary: In confirmed pediatric AHO obtain serum CRP on initial evaluation and monitor every 2–3 days early in therapy, then weekly or periodically until normalization or a clear trend is established.every 2–3 days early in course, then weekly
Pediatric ID Society/IDSA guideline.
Specimen types for CRP per WHO: venous whole blood, serum, or plasma
WHO lists CRP as an essential IVD; CRP preferred over ESR
Documentation Required
Hodgkin Lymphoma Workup — ESR Required per NCCN
Hodgkin lymphoma workup — follow NCCN recommendations. For adults with suspected or newly diagnosed Classic Hodgkin Lymphoma, ESR is considered essential and should be measured within six months of diagnosis as part of staging and risk classification. Include ESR in the initial diagnostic workup when following NCCN guidance.
NCCN lists ESR as 'essential' in the diagnostic/workup of Hodgkin Lymphoma (age ≥18) — test within 6 months of diagnosis
NCCN follow-up labs: CBC, platelets, chemistry profile, and ESR if ESR was elevated at initial diagnosis
Documentation Required
ESR Level and NCCN Treatment/Risk Stratification
ESR level informs staging, risk and radiation dosing decisions in Hodgkin Lymphoma. An ESR threshold (for example, ESR <50 mm/hr versus ≥50 mm/hr) is used by NCCN to define risk groups and to inform radiation dosing decisions (e.g., in non-bulky stage I–IIA disease, ESR <50 supports a 20 Gy dose after ABVD x2; ESR ≥50 is an unfavorable risk factor). Document measured ESR value in the record to support staging, treatment planning, and any coverage justification tied to NCCN-based management.
ESR <50 mm/hr vs ≥50 mm/hr is used in NCCN risk stratification and ISRT dosing decisions
Document numeric ESR result in the chart to support treatment planning and coverage
Outcome implicationRoutine CRP screening for early-onset neonatal sepsis was not supported by outcomes in the study; diagnostic performance considered insufficient for routine testing.
CRP and ESR thresholds referenced in guidelines (examples)
ACR pediatric MIS-C tiering exampleCRP ≥5 mg/L or ESR ≥40 mm/hr used as tier-one trigger for further testing.
PMR thresholds exampleESR >30–40 mm/hr commonly present in PMR per guideline discussions.
GCA thresholds exampleESR 40–60 mm/hr or markedly elevated CRP cited in guideline contexts for GCA evaluation.
Guidelines recommend 1–3 month intervals for active arthritis monitoring using composite measures including CRP or ESR.
Use in rheumatologyFrequency determined by disease activity and treatment response; monitor more frequently if signs/symptoms warrant.
ESR — test within six months of Hodgkin Lymphoma diagnosis and follow-up timeline
Hodgkin Lymphoma initial timingESR should be tested within six months of Hodgkin Lymphoma diagnosis (NCCN: ESR listed as 'essential').
Follow-up timelineNCCN follow-up: lab studies including ESR if elevated at diagnosis every 3–6 months for 1–2 years, then every 6–12 months for next 3 years, then annually.
Clinical useESR informs staging and may influence radiation dosing (e.g., ESR <50 used in ISRT dosing decisions).
ESR or CRP — every 3 months (example frequency)
Example frequency — PMR/GCA follow-upGuidance examples cite laboratory monitoring (ESR or CRP) at approximately every 3 months during steroid therapy or follow-up visits.
GCA monitoring noteGuidelines recommend ongoing clinical and laboratory monitoring; frequency individualized based on remission duration and therapy.
PMR initial and ongoing monitoringObtain CRP and/or ESR prior to therapy and monitor at clinic visits; some guidelines suggest monitoring as frequently as 1–4 weeks until remission.
CRP and/or ESR as part of disease activity measures — every 1–3 months
Disease activity monitoring frequencyCRP and/or ESR incorporated into disease activity measures and typically measured every 1–3 months while disease is active.
Use in composite scoresDAS28 and SDAI can use CRP or ESR; monitoring frequency aligns with disease activity and treatment target timelines.
Transition to less frequent monitoringOnce treatment targets are met, monitoring intervals may extend to every 6–12 months.
CRP — every 2–3 days initially, then weekly
Initial AHO monitoring frequencyIn pediatric AHO, obtain serum CRP on initial evaluation; measure every 2–3 days during early therapy, then weekly.
PurposeEarly serial CRP serves as baseline and for sequential monitoring after confirmed AHO; ESR is no longer routinely used for diagnosis in children.
CRP — every 2–3 days early in course, then weekly or periodic until normalization
Early course monitoringMeasure serum CRP every 2–3 days early in the course of pediatric AHO, then weekly or periodically until normalization or a clear trend is established.
ESR roleESR is not routinely recommended for pediatric AHO diagnosis; combined use with CRP may slightly improve sensitivity but thresholds are uncertain.
Clinical applicationRepeat testing frequency should be guided by clinical status rather than routine daily testing.
Treatment-initiation labs — obtain FBC, CRP and ESR for suspected GCA
When starting glucocorticoids for suspected GCA, obtain blood for full blood count, CRP and ESR before or immediately after commencing therapy; do not delay steroid therapy if GCA is strongly suspected.
Note
hsCRP and ESR requisition requirements
If hsCRP is desired for cardiovascular risk stratification it must be specifically requested on the laboratory requisition; ESR requires written indication in some jurisdictions per BC guidance.
Automated ESR methods and alternate techniques (e.g., EDTA-based) exist; results can differ substantially from Westergren and be affected by sample prep.
Noninflammatory influencesESR results are influenced by red blood cell morphology, temperature, anemia, renal disease, and other noninflammatory factors.
CRP and WHO preference
WHO preferenceWHO recommends CRP remain the preferred test to detect inflammation and monitor response, using ESR only where CRP is unavailable or in select conditions (e.g., SLE, low-grade bone/joint infections).
Specimen and assay guidanceWHO advises using the Westergren assay format for ESR and indicates CRP can be assayed on venous whole blood, serum, or plasma by various methods.
RationaleESR has high rates of false positives/negatives; CRP offers greater specificity in many settings.
ESR — WHO/ICSH discussion of Westergren method and nonspecific elevation
Westergren considerationsICSH data: only 28% of labs used Westergren exclusively; non-Westergren methods can deviate up to 142%—interpretative comments recommended.
ESR nonspecificityWHO and other sources note ESR is a nonspecific marker influenced by noninflammatory factors, increasing false positives/negatives.
Clinical implicationWhen reporting ESR from non-Westergren methods, labs should consider interpretative comments regarding method differences.
CRP and ESR — brief comparative definition
Comparative summaryCRP and ESR are acute-phase inflammation markers; CRP may be more sensitive and preferred in most settings while ESR can be informative in specific conditions (e.g., PMR relapse prediction, some SLE presentations).
Use togetherCombined CRP and ESR testing can increase sensitivity in selected contexts (e.g., PJI, though thresholds vary).
Interpretation caveatBoth tests are adjunctive and must be interpreted with clinical findings and other diagnostics.
Laboratory-developed test (LDT) definition
LDT definitionLaboratory-developed tests (LDTs) are tests developed and validated in-house and are regulated by CMS under CLIA as high-complexity tests; they are not FDA-cleared/approved for clinical use.
Regulatory contextFDA clearance/approval is not required for clinical use of LDTs, but CLIA oversight applies.
ApplicabilityMany CRP and ESR assays may be performed as FDA-approved assays or as LDTs depending on the laboratory.
hsCRP definition (high-sensitivity CRP for cardiovascular risk)
hsCRP purposeHigh-sensitivity CRP (hsCRP) is used for cardiovascular risk stratification and should be specifically requested when desired.
Assay availabilityFDA has approved hsCRP assays; hsCRP is distinct from conventional CRP in analytical sensitivity for low-level concentrations.
Ordering noteIf hsCRP is desired for CV risk assessment it must be requested on the laboratory requisition per guidance.