ModifiedPremera BluecrossPolicy N/A

Testing for Vector-Borne Infections

This policy defines which laboratory tests for arthropod-borne infections (viruses, bacteria, protozoa) are considered reimbursable or not reimbursable and specifies clinical indications and specimen/test types for Premera BlueCross members.

Policy Summary

PayerPremera Bluecross

PolicyTesting for Vector-Borne Infections

Policy CodePolicy N/A

Change TypeMaterial revision — coverage rules and coding update

Effective DateFeb 6, 2026

Next Review DateN/A

Key ActionDocument clinical signs, specimen type and timing and ensure testing uses the specified diagnostic method to support reimbursement.

SourceLink

POLICY UPDATE CHANGES

New policy adds reimbursement rules specifying that testing for listed vector-borne infections is reimbursable only when performed using the specific diagnostic methods and clinical indications outlined in this policy.

Coding update removed CPT codes 86382, 86790, 87207, 87449, 87798, 87899.

11Vector-borne infections named

PCR preferred earlyPCR preferred early

≤3 repeatsMalaria microscopy repeat limit

Codes enumeratedCPT/Proprietary codes listed

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Serologic confirmatory rise

Reimbursable and Non-reimbursable Testing Criteria

Babesiosis

Covered when specific clinical suspicion exists for the listed conditions

Babesiosis diagnostics: For individuals suspected of having babesiosis, Giemsa- or Wright-stain of a blood smear or nucleic acid amplification testing (NAAT) on blood is reimbursable; IgG or IgM indirect immunofluorescence antibody (IFA) assays for Babesia are not reimbursable.

See Note 1 in Related Information for clinical signs

Relapsing fevers and selected arboviruses

Covered when specific clinical suspicion exists for relapsing fevers and arboviral infections

Relapsing fever (Borrelia spp.): HTRF: serologic assays or PCR for Borrelia miyamotoi; LBRF: peripheral blood smear microscopy or PCR for Borrelia recurrentis; STRF/TBRF: dark-field microscopy, Giemsa- or Wright-stained blood smear microscopy, PCR for Borrelia spp., or serologic assays for Borrelia antibodies. Culture testing for Borrelia is not reimbursable.

See Notes 2-4 in Related Information

Chikungunya: For suspected chikungunya, viral culture, NAAT of serum, or IFA IgM testing during both acute and convalescent phases are reimbursable.

See Note 5 in Related Information

Colorado tick fever (CTF): For suspected CTF, PCR testing or IFA for CTF-specific IgM antibodies is reimbursable.

See Note 6 in Related Information

Dengue, Zika, West Nile, Yellow fever

Covered with timing/travel/pregnancy criteria for dengue, Zika, yellow fever, and West Nile virus

Dengue virus (DENV): For suspected DENV, NAAT, MAC-ELISA (IgM), NS1 ELISA, and confirmatory plaque reduction neutralization test (PRNT) are reimbursable. IgG ELISA and hemagglutination testing for DENV are not reimbursable.

Use NAAT/NS1 in acute phase per guidance

Zika virus (NAAT): NAAT is reimbursable for symptomatic pregnant individuals up to 12 weeks after symptom onset when there is residence/travel/sexual exposure to areas with current or past Zika transmission; NAAT is reimbursable for symptomatic non-pregnant individuals with recent travel to areas with an active CDC Zika Travel Health Notice when symptoms began within 7 days. Additional pregnancy/fetal/infant indications (e.g., fetal ultrasound findings, infants born to exposed parents) are reimbursable per policy.time-based: up to 12 weeks for symptomatic pregnant individuals; within 7 days for symptomatic non-pregnant travelers

Some non-travel symptomatic non-pregnant US-only individuals are not reimbursable

West Nile virus (WNV):

Ehrlichiosis/Anaplasmosis, Malaria, Rickettsial diseases

Covered when clinically suspected for ehrlichiosis/anaplasmosis, malaria, and rickettsial disease

Ehrlichiosis/Anaplasmosis: For suspected ehrlichiosis or anaplasmosis, NAAT of whole blood, IFA IgG, or microscopy for morulae detection are reimbursable; IFA IgM and standard blood culture are not reimbursable.

See Note 8 in Related Information; serology not recommended for acute diagnosis alone

Malaria: For suspected malaria, rapid immunochromatographic diagnostic tests (RDTs) or smear microscopy (Giemsa-stained thick and thin films) to diagnose malaria, determine species, identify life-cycle stage, and/or quantify parasitemia are reimbursable; microscopy may be repeated up to three times within three days if initial microscopy is negative; PCR to confirm species in a diagnosed malaria case is reimbursable.repeat: up to 3 times within 3 days if initial microscopy is negative

See Note 9 in Related Information

Rickettsial disease: For suspected tickborne rickettsial disease, IFA IgG performed on two specimens at least two weeks apart (paired acute and convalescent sera) is reimbursable to demonstrate a fourfold rise; standard blood culture, NAAT, or IFA IgM alone are not reimbursable.

Testing modality criteria

Guidance on appropriate diagnostic testing depending on pathogen and clinical context:

Malaria testing: Use parasite-based diagnosis including STAT microscopic examination of Giemsa-stained thick and thin blood smears and antigen RDTs as adjuncts; NAAT/PCR is more sensitive for low parasitemia and can identify species with an estimated PCR limit of detection of ~0.02–1 parasite/µL and may be used as a gold standard in some settings.

Repeat microscopy every 12–24 hours up to 3 times before ruling out when suspicion persists

Arboviral testing (WNV, dengue, Zika, chikungunya, yellow fever): Use IgM MAC-ELISA or IFA for symptomatic WNV and other arboviruses; PCR/NAAT is primarily useful in immunocompromised patients, early illness for dengue/Zika (NAAT preferred within 7 days for dengue; RT-PCR establishes Zika diagnosis in symptomatic patients), or for specific specimens (e.g., urine for Zika NAAT); consider PRNT at reference labs for confirmatory testing when cross-reactivity is a concern.

Serology may be insensitive early; PRNT available only at select public health labs

Tickborne rickettsial and ehrlichial/anaplasma testing: Follow CDC/IDSA guidance: perform paired acute and convalescent IFA IgG for rickettsial diseases with a ≥4-fold rise for confirmation; PCR on whole blood is useful early for ehrlichiosis/anaplasmosis though PCR sensitivity for Rickettsia rickettsii in whole blood is low except in severe disease; microscopy for morulae can support ehrlichia/anaplasma diagnosis. Culture for obligate intracellular rickettsiae is not routinely used.

Pathogen-specific diagnostic criteria

Testing recommendations by pathogen and clinical context:

Borrelia spp.: For Lyme neuroborreliosis use two-tiered serologic testing; for CSF neuroborreliosis consider paired serum and CSF collected within 24 hours and CSF/serum antibody index; NAAT may be used for tissue/biopsy specimens; serum is the optimum specimen for standard serology.

References: IDSA/ASM guidance

Borrelia miyamotoi: Primary test for acute B. miyamotoi infection is NAAT on blood; serology (EIA for GlpQ) on serum can detect antibodies but NAAT is preferred for acute diagnosis.

Anaplasma/Ehrlichia: Primary test for acute infection is NAAT on whole blood; Wright/Giemsa smear of peripheral blood or buffy coat during the first week is an alternate if NAAT is unavailable; acute and convalescent IFA IgG titers are for retrospective diagnosis; immunohistochemistry may be used for tissue specimens.

Ehrlichia ewingii definitive assay: NAAT; smear less sensitive

Reimbursable testing criteria

Covered when ALL of the following are met

Coverage condition: Testing is reimbursable only when (1) the test is for one of the listed vector-borne infections and (2) it is performed using the specific diagnostic methods outlined in this policy and (3) the clinical indications and timing criteria described in the policy are met.

Asymptomatic screening and testing outside these indications are not reimbursable.

The policy lists specific laboratory methods that are not reimbursable for certain vector‑borne infections. Examples include: IgG or IgM IFA for Babesia (Babesia serology), culture testing for Borrelia in relapsing fever, and IFA IgM or standard blood culture for rickettsial diseases. These named exclusions reflect the limited clinical utility, diagnostic performance, or biosafety/availability constraints of those methods in routine practice.

Serologic assays (including IFA and IgM tests) can be unreliable early in infection because antibodies may be undetectable during the first days of illness; the policy notes that serology is typically insensitive during the first week and may yield false positives for IgM. For early detection, molecular methods such as NAAT/PCR on appropriate specimens (e.g., whole blood, serum, urine or CSF depending on pathogen and presentation) are preferred for many acute infections (for example, NAAT for Zika or for Anaplasma/Ehrlichia in the first week). The policy also specifies that NAAT for West Nile virus is reimbursable for immunocompromised individuals but is not reimbursable for immunocompetent persons in routine evaluation.

The policy explains that culture and some rapid diagnostic tests have accuracy and availability limitations. Culture of obligate intracellular organisms (for example many rickettsiae and some Borrelia species) is rarely used because specialized cell culture methods and biosafety facilities are required, and routine blood culture is therefore not reimbursable for rickettsial disease. Rapid immunochromatographic tests (e.g., BinaxNOW malaria RDT) have variable sensitivity and may misclassify species or generate false positives in non‑endemic settings, so RDTs are described as adjuncts that often require confirmatory microscopy or reference testing.

For early, localized Lyme disease manifesting as erythema migrans (EM), the policy states that testing is not routinely recommended. Clinical diagnosis of solitary EM should guide initial management rather than serologic testing, and serologic approaches (two‑tier testing) are reserved for later or disseminated presentations where timing and paired sera are appropriate.

The policy alerts clinicians that serology alone is not recommended as the sole diagnostic test for several acute infections (for example babesiosis and anaplasmosis) because antibody responses do not reliably distinguish acute from past infection. Where serology is used for rickettsial infections, confirmation requires paired acute and convalescent IgG testing demonstrating a fourfold rise in titer; single or inappropriately timed serologic results can be misleading.

Testing that uses methods other than those specified in this policy, testing performed outside the clinical indications described, and routine screening of asymptomatic individuals are not reimbursable. The policy clarifies that reimbursement is limited to testing for listed vector‑borne pathogens when the specific diagnostic method and clinical indications in the policy are met.

Examples of asymptomatic testing considered not medically necessary include screening during a general examination for babesiosis, chikungunya, Colorado tick fever, dengue (DENV), ehrlichiosis/anaplasmosis, malaria, rickettsial disease, tickborne relapsing fever, West Nile virus, yellow fever, or Zika virus in individuals without abnormal findings. The policy explicitly states that such asymptomatic screening is not reimbursable.

The policy cautions that an isolated serologic result — for example a single mildly elevated IgG or an isolated IgM — without paired convalescent testing or confirmatory methods may be insufficient for diagnosis. Guidelines cited in the policy recommend demonstrating a fourfold rise in IgG titer between acute and convalescent specimens (typically taken 2–4 weeks apart) to confirm recent infection, and they note that IgM assays are prone to false positives and prolonged elevation.

Consistent with the policy’s overall coverage rule, screening asymptomatic individuals for the listed vector‑borne infections is considered not medically necessary and not reimbursable. Reimbursement is limited to situations meeting the policy’s specified clinical indications and use of the stated diagnostic modalities.

Codes and Test Identifiers

Covered CPT Codes (listed)CPT

86280	Hemagglutination inhibition test (HAI)
86619	Antibody; Borrelia (relapsing fever)
86666	Antibody; Ehrlichia
86753	Antibody; protozoa, not elsewhere specified
86757	Antibody; Rickettsia
86788	Antibody; West Nile virus, IgM
86789	Antibody; West Nile virus
86794	Antibody; Zika virus, IgM
87040	Culture, bacterial; blood, aerobic, with isolation and presumptive identification of isolates
87468	Infectious agent detection by nucleic acid (DNA or RNA); Anaplasma phagocytophilum, amplified probe technique

1–10 of 14

1/2

Proprietary/HCPCS CodesHCPCS

0043U	Tick - borne relapsing fever Borrelia group, antibody detection to 4 recombinant protein groups, by immunoblot, IgM Proprietary test: Tick - Borne Relapsing Fever Borrelia (TBRF) ImmunoBlots IgM Test Lab/Manufacturer: IGeneX Inc.
0044U	Tick - borne relapsing fever Borrelia group, antibody detection to 4 recombinant protein groups, by immunoblot, IgG Proprietary test: Tick - Borne Relapsing Fever Borrelia (TBRF) ImmunoBlots IgG Test Lab/Manufacturer: IGeneX Inc.

No explicit CPT/HCPCS/ICD codes in this sectionmixed

No codes listed

FDA approved diagnostic device identifiersFDA

K170940	Rickettsia Real -Time PCR Assay (CDC) - FDA definition/approval
K083744	BinaxNOW Malaria Positive Control Kit - FDA approval

FDA-approved WNV ELISA modelsFDACovered

EL0300G	West Nile Virus ELISA IgG model EL0300G by Focus Technologies, Inc.
EL0300M	West Nile Virus IgM Capture ELISA model EL0300M by Focus Technologies, Inc.

Removed CPT CodesCPT

86382	Removed CPT code
86790	Removed CPT code
87207	Removed CPT code
87449	Removed CPT code
87798	Removed CPT code
87899	Removed CPT code

Serologic confirmation threshold

Serologic confirmation thresholdDemonstration of at least a fourfold rise in antibody titer between acute and convalescent serum samples is required to confirm acute infection.

Paired sera timingCollect an acute specimen early after symptom onset and a convalescent specimen 2–4 (or 2–10) weeks later for comparison.

Single elevated titer not sufficientElevated titers alone are not sufficient to diagnose tickborne rickettsial diseases without seroconversion.

Provider Actions, Documentation, and Billing Advisories

Documentation Required

Specialized laboratory referral may be needed

Refer tests to specialized/reference laboratories when required by the assay or public health guidance (for example, CDC Arbovirus Diagnostic Laboratory or state public health labs) — some assays and confirmatory tests (e.g., PRNT for flaviviruses, specialized immunoblots for TBRF) are available only at reference labs.

Examples: PRNT for dengue/other flaviviruses; CDC Rickettsia Real‑Time PCR; proprietary TBRF immunoblots at commercial reference labs

Note

Assay approvals and LDTs — no additional prior authorization specified

FDA‑approved assays exist for several vector‑borne infections (e.g., FDA‑cleared West Nile IgM/IgG EIAs, CDC Rickettsia Real‑Time PCR approval, BinaxNOW malaria positive control). Many other tests are laboratory‑developed tests (LDTs) that require CLIA high‑complexity validation but are not FDA cleared/approved. The presence of FDA approval for specific assays does not imply any additional prior authorization requirements are specified in this policy.

FDA‑cleared/approved examples: multiple WNV ELISA kits, CDC Rickettsia Real‑Time PCR, BinaxNOW control kit

Background and Rationale

Arthropod vectors — including mosquitoes, ticks, fleas, and mites — transmit a range of pathogens (bacteria, protozoa, and viruses) that cause vector‑borne illnesses such as malaria, babesiosis, rickettsial diseases, relapsing fevers, and arboviral infections (e.g., dengue, Zika, West Nile, yellow fever, chikungunya). Diagnostic approaches vary by pathogen and clinical context and include microscopy (blood smears), NAAT/PCR, serology (IFA/ELISA), antigen tests, and culture in specialized settings, with choice guided by timing of illness, specimen type, and test performance characteristics.

Terms and Test Method Definitions

Arboviruses — examples

Examples of arbovirusesArthropod-borne viruses include Zika virus, West Nile virus (WNV), chikungunya virus, dengue virus (DENV), yellow fever virus (YFV), and Colorado tick fever virus (CTF).

VectorsTransmitted by arthropod vectors such as mosquitoes, ticks, fleas, and mites.

Disease typesArboviruses cause viral infections; other arthropod-borne agents include protozoa (e.g., Plasmodium, Babesia) and bacteria (e.g., Rickettsia, Borrelia).

NAAT — definition and context

DefinitionNAAT (nucleic acid amplification testing) refers to molecular methods that amplify and detect pathogen DNA or RNA, including PCR and RT-PCR.

SpecimensNAATs can be performed on serum, whole blood, tissue, CSF, and FFPE specimens depending on the pathogen.

Policy Changes and Effective Dates

2025-11-01policy_created

New policy approved Oct 14, 2025 and announced 11/01/25; defines reimbursable testing for listed vector-borne infections only when using specified diagnostic methods and clinical indications (asymptomatic screening and other methods not reimbursable).

2026-02-06coding_updateLatest

Coding update removed CPT codes 86382, 86790, 87207, 87449, 87798, and 87899; effective for dates of service on or after Feb 6, 2026.

Policy Summary

PayerPremera Bluecross

PolicyTesting for Vector-Borne Infections

Policy CodePolicy N/A

Change TypeMaterial revision — coverage rules and coding update

Effective DateFeb 6, 2026

Next Review DateN/A

Key ActionDocument clinical signs, specimen type and timing and ensure testing uses the specified diagnostic method to support reimbursement.

SourceLink

On This Page

For suspected WNV, IFA (or MAC-ELISA) for WNV-specific IgM or IgG in serum or CSF and confirmatory PRNT are reimbursable; nucleic acid detection (NAAT) for WNV is reimbursable for immunocompromised individuals but is not reimbursable for immunocompetent individuals.

See Notes 11-12 in Related Information

Yellow fever virus (YFV): For suspected YFV, NAAT or serologic assays to detect virus-specific IgM and IgG, plus confirmatory PRNT, are reimbursable.

paired serology min 2 weeks apart; demonstration of ≥4-fold rise recommended

See Note 10 in Related Information

Document specimen timing; IFA insensitive in first week—collect acute and convalescent samples 2–4 (or 2–10) weeks apart

Rickettsia: Diagnostic approach includes serology (paired acute and convalescent IFA IgG/IgM) and NAAT; optimum specimens include serum and skin biopsy/autopsy tissue; immunohistochemical staining of tissue may detect antigens early after symptom onset or antibiotic administration.

Document paired sera 2–4 (or 2–10) weeks apart to demonstrate ≥4-fold rise

Babesia: Primary tests are Giemsa/Wright-stained thick and thin blood smears and NAAT on blood; serology (acute and convalescent IFA IgG) is not recommended for acute infection though may assist in low parasitemia cases.

PCRs often preferentially detect B. microti

Malaria (Plasmodium spp.): STAT microscopic examination of Giemsa-stained thick and thin blood films is the standard; repeat every 12–24 hours up to three exams before ruling out; RADTs are adjunctive and require confirmatory blood films; PCR from reference labs can detect and differentiate species.

AAP/IDSA guidance

Dengue Virus (DENV): Detect DENV RNA by NAAT for patients within 7 days of symptom onset; NS1 antigen detection is an acceptable alternative in the acute phase; serology is limited by cross-reactivity and PRNT is reference standard when available.

WHO and IDSA/ASM recommendations

Zika Virus (ZIKV): Use serum/plasma/CSF and urine for NAAT; molecular assays are preferred early after symptom onset; serology interpretation is challenged by flavivirus cross-reactivity; special testing considerations apply for pregnant women and infants exposed in utero.

WHO guidance; RT-PCR establishes diagnosis in symptomatic patients

West Nile Virus (WNV): Laboratory diagnosis is typically by detection of virus-specific IgM and/or IgG in serum or CSF; PCR from CSF is relatively insensitive for neuroinvasive disease and may be reserved for specific clinical contexts.

Antibody cross-reactivity among flaviviruses may confound results; consider PRNT for confirmation

LDTs must meet CLIA high‑complexity validation

Note

Diagnostic sequencing guidance — NAAT/antigen early, serology for convalescent confirmation

Testing should follow clinical indications and timing described in this policy and in national guidance (CDC, IDSA, WHO). Use the recommended diagnostic sequencing: NAAT/NS1 antigen testing early in acute illness (typically within 7–10 days for many arboviruses), and serology (IgM/IgG, IFA) later or for convalescent confirmation. For malaria, perform STAT microscopy (thick and thin) immediately and repeat as indicated; confirm RDTs with microscopy. Do not rely on a single, inappropriately timed serologic test.

Early acute phase: NAAT or NS1 antigen (when applicable)
Later/convalescent: Serology (paired samples) for confirmation
Malaria: STAT microscopy (repeat 12–24 h, up to 3 exams) and confirm RDTs by microscopy

Denial Risk

Prior authorization and denial risk — none explicitly required; denials possible if testing falls outside policy

There are no explicit prior authorization requirements or additional denial triggers specified in this section beyond those general coverage limits in the policy. Testing that does not meet the clinical indications, timing, or methods described may be denied.

No policy‑specified prior authorization for listed tests
Testing outside specified indications/methods or screening of asymptomatic individuals may be denied

Prior Authorization

Timely microscopy — provide STAT results, do not batch

Perform microscopy and report results immediately — do not delay or batch microscopy so that results are unavailable within ≤24 hours of presentation. Microscopy for malaria and smear/buffy coat examination for ehrlichiosis/anaplasmosis should be available urgently and interpreted by experienced microscopists.

Microscopy results should be available ≤24 hours
Do not batch or delay microscopy to await specialist availability
Immediate STAT blood smears for suspected malaria (repeat as recommended)

Documentation Required

Rickettsial disease testing — minimum two IFA IgG tests (paired sera)

For suspected rickettsial disease, perform at least two IFA IgG tests: one acute specimen collected early and a convalescent specimen collected a minimum of two weeks later (commonly 2–4 or 2–10 weeks apart). A fourfold rise in titer between paired sera is required to confirm acute infection; single or improperly timed serologic tests can be misleading.

Obtain paired acute and convalescent sera ≥2 weeks apart (typically 2–4 or up to 2–10 weeks)
Require demonstration of ≥4‑fold rise in IgG titer for confirmation

Documentation Required

Clinical documentation to support testing — record symptoms, exposure, specimen type, and collection dates

Document clinical presentation, epidemiologic exposure, timing of symptom onset, specimen type(s), and collection dates for all tests. For paired serology, clearly record both collection dates and clinical correlation. Support testing with signs/symptoms consistent with the targeted infection and the rationale for the chosen diagnostic method.

Document: signs/symptoms, travel/exposure history, symptom onset date
Document specimen type and each sample collection date (especially for paired sera)
Document which diagnostic method was used and why (NAAT, IFA, microscopy, antigen, etc.)

Documentation Required

Serology and paired serology documentation — collect acute + convalescent samples and consider confirmatory testing

When ordering serologic testing, collect and retain appropriately timed acute and convalescent specimens per guidance: acute phase sample early in illness and convalescent sample 2–4 (or 2–10) weeks later. Note that serologic assays can cross‑react (especially flaviviruses); confirmatory testing (e.g., PRNT) or testing at specialized labs may be required when cross‑reactivity is possible.

Paired serology collection timing: acute and convalescent 2–4 (or 2–10) weeks apart
Consider PRNT or reference‑lab testing to resolve flavivirus cross‑reactivity

Availability/limitsNAATs are specific and sensitive but may not be available at all laboratories and can be costly; performance varies by specimen and organism.

NAAT / PCR / qPCR / RT-PCR — definitions and use

NAAT / PCR / qPCR / RT-PCREnzyme-dependent nucleic acid amplification methods (PCR, quantitative PCR, real-time RT-PCR) used to detect and quantify pathogen DNA or RNA; often preferred for early infection detection.

Specimen typesUsed on blood, CSF, plasma, tissue, urine or other appropriate specimens depending on the pathogen and clinical scenario.

PerformanceHigh specificity and sensitivity for many acute infections, but sensitivity can vary by organism and sample source.

Serologic assay definitions

IFA / ELISA / MAC-ELISA / MIFSerologic assays used to detect IgG or IgM antibodies: IFA (indirect immunofluorescence), ELISA (enzyme-linked immunosorbent assay), MAC-ELISA (IgM antibody capture ELISA), and MIF (microimmunofluorescent assays).

Clinical roleUseful for demonstrating seroconversion or retrospective diagnosis; limited utility early in infection due to delayed antibody responses and potential cross-reactivity.

Confirmatory testingPlaque reduction neutralization tests (PRNT) may be used as confirmatory assays for flavivirus antibody specificity at specialized labs.

NAAT — definition and diagnostic characteristics

NAAT definitionNucleic acid amplification testing detects pathogen DNA or RNA using techniques such as PCR and RT-PCR and is often more sensitive in early or low-burden infections.

Diagnostic characteristicsNAATs are specific and sensitive but availability, cost, and sample-dependent sensitivity vary; some NAATs detect only select species (e.g., many babesiosis PCRs detect B. microti).

Use casesPreferred for acute infection detection for pathogens like Anaplasma, B. miyamotoi, dengue (early), and others when performed on appropriate specimens.

RDT — definition and accuracy caveat

Rapid diagnostic test (RDT)Point-of-care immunochromatographic assays that detect antigen or antibody for rapid results.

Accuracy caveatRDTs have variable sensitivity and specificity; performance may be reduced in non-endemic settings and results often require confirmation by microscopy or NAAT.

Use in malariaRDTs can be used as adjuncts for malaria diagnosis but should be confirmed with blood films and may miss low parasitemia or non-falciparum species.

IFA — definition and paired sera requirement

IFA definitionIndirect immunofluorescence antibody (IFA) assay detects IgG and IgM antibodies to pathogens and is a standard serologic reference for many tickborne rickettsial infections.

Sensitivity/timingIFA assays are insensitive during the first week of illness; a paired acute and convalescent specimen is required for confirmation.

Paired sera requirementPerform at least two IFA IgG tests (acute and convalescent) collected a minimum of 2–4 (up to 2–10) weeks apart to demonstrate seroconversion (≥4-fold rise).

IFA — key points (duplicate entry)

IFA definition (duplicate)Indirect immunofluorescence antibody assay—used to detect pathogen-specific IgG/IgM; requires paired sera for confirmation and is insensitive early in illness.

Confirmatory criterionA fourfold rise in IgG titer between acute and convalescent sera is considered confirmatory evidence of acute infection.

LimitationsSingle or inappropriately timed serologic tests can lead to misinterpretation of results.

PCR — key points (duplicate entry)

PCR definition (duplicate)Polymerase chain reaction (PCR) is a NAAT used to amplify and detect pathogen DNA; useful early in infection but sensitivity varies by organism and specimen.

Sensitivity notePCR of whole blood for Rickettsia rickettsii has low sensitivity except in severe disease; PCR is useful early for ehrlichiosis/anaplasmosis.

Specimen dependencePerformance depends on specimen type (e.g., blood, CSF, tissue) and timing relative to symptom onset.

NAAT preferred for acute infection detection

NAAT preferred for acute detectionNAAT/PCR is preferred for early detection of several infections — e.g., blood NAAT for Anaplasma and Borrelia miyamotoi, RT-PCR/NAAT for dengue and Zika in acute phase.

Specimen examplesPreferred specimens include whole blood for Anaplasma, blood/CSF/plasma/urine for arboviruses, and blood for babesiosis PCR.

Use in immunocompromisedNAAT may be specifically indicated in immunocompromised individuals (e.g., WNV nucleic acid testing in immunocompromised patients).

Serology (IFA/ELISA/PRNT) uses and PRNT as reference

Serology usesSerologic assays (IFA, ELISA, PRNT) are used for diagnosis of many arboviruses and rickettsial infections, particularly for retrospective or convalescent diagnosis.

PRNT rolePlaque reduction neutralization test (PRNT) is considered the reference standard for flavivirus (e.g., dengue) neutralizing antibody testing but is available only at select public health labs.

Cross-reactivity cautionSerologic assays can cross-react among flaviviruses; confirmatory testing (e.g., PRNT) may be needed when cross-reactivity is suspected.

References and guidelines

Key referencesGuidance and references cited include CDC guidance, American Academy of Pediatrics Red Book, WHO laboratory testing guidance, IDSA/ASM utilization guide, and other clinical resources.

Selected organizationsCDC, AAP, WHO, IDSA/ASM, IEC, and FDA are specifically referenced for diagnostic recommendations and assay approvals.

PRNT and specialized testingPRNT and certain advanced diagnostics are available at public health or reference labs per CDC/WHO guidance.