{
  "registry": "KnowYourPrime Evidence Registry",
  "license": {
    "name": "CC BY 4.0",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Credit KnowYourPrime and link to the finding URL."
  },
  "fields": {
    "devices": "Devices this finding names, including models it says it does not cover. What was actually tested is in scope.applies_to; exclusions are in scope.does_not_cover.",
    "evidence": "Studies by role: anchor (the rating rests on it), conflicting, null_result, supporting.",
    "industry_ties": "Device-maker ties listed in Europe PMC metadata: author_affiliations names makers an author lists as an affiliation, funders names makers listed as funding. stated_ties holds ties a paper states only in its own conflict, funding or acknowledgement text, each read from that statement and worded to say only what it says. Sources are Europe PMC metadata, funding printed in the abstract, and those reviewed statements. An empty list means no tie was found there, not that the study is independent: many papers have no open full text to read. Metadata, not a judgment of the study. checked false means no Europe PMC metadata was available."
  },
  "id": "KYP-ER-0013",
  "version": "1.0",
  "reviewed": "2026-10-24",
  "url": "https://knowyourprime.com/evidence-sudden-hrv-drop-before-illness",
  "title": "Overnight HRV Drop Before an Infection",
  "question": "Can a sudden drop in overnight heart rate variability signal an infection before symptoms start?",
  "measurement": "Heart rate variability (HRV)",
  "devices": [
    "Oura",
    "Garmin",
    "WHOOP",
    "Wearables"
  ],
  "rating": {
    "label": "Emerging",
    "code": "emerging",
    "definition": "Evidence currently favors the claim, but more confirmation is needed.",
    "rule_version": "1.4",
    "rule_reasons": [
      "Anchor-grade evidence affirms the core relationship.",
      "Multiple supporting studies are consistent with the core relationship.",
      "The claim rests on a single anchor whose finding affirms it; a second independent affirming anchor is needed to reach Established."
    ]
  },
  "conclusion": "It can, on thin direct evidence. In the one study that tested HRV alone, seven athletes’ morning HRV fell below their own baseline on the two days before a confirmed COVID-19 infection, and large wearable studies detected infection days before testing using HRV combined with other signals. A drop is consistent with an oncoming illness, and the same evidence cannot say that any one drop means one.",
  "reasoning": [
    "The claim is about timing: whether HRV falls before an infection shows itself, not only during it. Only one study tested that with HRV on its own, against each person’s own baseline, and it found the drop.",
    "Large studies of Oura and Garmin wearers point the same way, detecting COVID-19 about two to three days before testing, but their models combine HRV with temperature, resting heart rate and other signals, so they support the direction without isolating HRV. With one clean anchor and several consistent supporting studies, the rule rates the claim Emerging: the evidence favors it and needs a second independent test to be Established."
  ],
  "key_results": [
    {
      "text": "In seven elite female soccer players with at least 30 days of morning HRV recorded beforehand, LnRMSSD was significantly lower than each player’s own baseline on the two days before a PCR-confirmed COVID-19 infection and through the first four days after the positive test.",
      "source": "doi:10.1038/s41598-025-10747-y",
      "source_url": "https://doi.org/10.1038/s41598-025-10747-y",
      "source_citation": "Parpa et al., Scientific Reports, 2025"
    },
    {
      "text": "Across 9,381 Department of Defense personnel wearing Garmin and Oura devices (599,174 user-days, 491 COVID-19 cases), a real-time model identified infection before testing with an AUC of 0.82, its risk score rising an average of 2.3 days early. The model was multimodal and did not isolate HRV.",
      "source": "doi:10.1038/s41598-022-07764-6",
      "source_url": "https://doi.org/10.1038/s41598-022-07764-6",
      "source_citation": "Conroy et al., Scientific Reports, 2022"
    },
    {
      "text": "In the TemPredict study, an Oura Ring classifier trained on 73 confirmed cases identified COVID-19 an average of 2.75 days before testing (AUC 0.819); adding continuous temperature raised the AUC by 4.9 percent.",
      "source": "doi:10.1038/s41598-022-07314-0",
      "source_url": "https://doi.org/10.1038/s41598-022-07314-0",
      "source_citation": "Mason et al., Scientific Reports, 2022"
    },
    {
      "text": "In 23 soldiers measured on two days, resting RMSSD had good day-to-day reliability (ICC 0.823), so a day-to-day change in RMSSD is more likely real than noise; SDNN was only moderately reliable (ICC 0.689).",
      "source": "doi:10.1136/military-2024-002687",
      "source_url": "https://doi.org/10.1136/military-2024-002687",
      "source_citation": "Chapman et al., BMJ Military Health, 2025"
    }
  ],
  "scope": {
    "applies_to": "Overnight or morning resting HRV compared with a person’s own recent baseline, before the onset of an acute infection, mainly COVID-19.",
    "does_not_cover": "Telling an infection from the many other causes of a low HRV night, such as alcohol, hard training, poor sleep or stress; diagnosis; any infection other than those studied."
  },
  "limitations": [
    "The only HRV-specific test followed seven people.",
    "The large detection studies combine several signals, so the share of the warning that comes from HRV is unknown.",
    "Most evidence comes from COVID-19, which may not generalize to other infections."
  ],
  "evidence": {
    "anchor": [
      {
        "key": "doi:10.1038/s41598-025-10747-y",
        "title": "Heart rate variability in female soccer players, before, during, and after a COVID-19 positive test.",
        "first_author": "Parpa",
        "journal": "Scientific reports",
        "year": 2025,
        "url": "https://doi.org/10.1038/s41598-025-10747-y",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      }
    ],
    "supporting": [
      {
        "key": "doi:10.1136/military-2024-002687",
        "title": "Day-to-day reliability of basal heart rate and short-term and ultra short-term heart rate variability assessment by the Equivital eq02+ LifeMonitor in US Army soldiers.",
        "first_author": "Chapman",
        "journal": "BMJ military health",
        "year": 2025,
        "url": "https://doi.org/10.1136/military-2024-002687",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.2196/76218",
        "title": "Using Patient-Held Devices to Measure Variations in Resting Heart Rate and Step Count Prior to Presentation With an Acute Illness: International, Multicenter Flash Mob Feasibility Study.",
        "first_author": "den Duijn",
        "journal": "JMIR cardio",
        "year": 2025,
        "url": "https://doi.org/10.2196/76218",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1038/s41598-022-07314-0",
        "title": "Detection of COVID-19 using multimodal data from a wearable device: results from the first TemPredict Study.",
        "first_author": "Mason",
        "journal": "Scientific reports",
        "year": 2022,
        "url": "https://doi.org/10.1038/s41598-022-07314-0",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [],
          "funders": [
            "Oura"
          ],
          "stated_ties": []
        }
      },
      {
        "key": "doi:10.1038/s41598-022-07764-6",
        "title": "Real-time infection prediction with wearable physiological monitoring and AI to aid military workforce readiness during COVID-19.",
        "first_author": "Conroy",
        "journal": "Scientific reports",
        "year": 2022,
        "url": "https://doi.org/10.1038/s41598-022-07764-6",
        "industry_ties": {
          "checked": true,
          "author_affiliations": [
            "Philips"
          ],
          "funders": [],
          "stated_ties": []
        }
      }
    ]
  },
  "evidence_last_evaluated": "Oct 24, 2026",
  "rating_history": [
    {
      "date": "2026-09-29",
      "rating": "Emerging",
      "from": null,
      "rule_version": "1.4"
    }
  ],
  "versions": [
    {
      "version": "1.0",
      "date": "2026-10-24",
      "rating": "Emerging",
      "change": "First published."
    }
  ],
  "research_desk": "https://knowyourprime.com/research-desk-hrv#acute-drop-infection",
  "related_findings": [
    "https://knowyourprime.com/evidence-wearable-hrv-accuracy",
    "https://knowyourprime.com/evidence-normal-hrv-by-age"
  ],
  "related_articles": [
    "https://knowyourprime.com/sudden-hrv-drop",
    "https://knowyourprime.com/what-improves-recovery-scores"
  ],
  "methodology": "https://knowyourprime.com/methodology",
  "citation": "KnowYourPrime Evidence Registry, Finding KYP-ER-0013, version 1.0, reviewed 2026-10-24. https://knowyourprime.com/evidence-sudden-hrv-drop-before-illness"
}