parsing-lab-values

Parsing lab values

Lab results in clinical text arrive as a value, a unit, and a reference range ("Sodium 132 mmol/L (135–145)"). To act on them you need a structured abnormal flag — is 132 low, normal, high, or critical? OpenMed's openmed.clinical lab helpers parse the reference range deterministically and derive the flag, honoring any explicit flag the originating lab already supplied. The helpers are unit-agnostic by design: they compare numbers within a stated range and never convert units, so a mmol/L value is never silently compared against a mg/dL range.

When to use

• After extracting-clinical-entities surfaces lab/measurement entities and you need to classify each as low / normal / high / critical.
• The user asks to parse reference ranges, flag abnormal labs, build a flagged labs table, or interpret values like <5, >=10, 0.5 - 1.2.
• You have an originating-lab flag (H, L, C, HH) and want it honored over a derived comparison.

Quick start

from openmed.clinical import (
    parse_reference_range, derive_abnormal_flag, LAB_FLAG_ADVISORY,
)

# Closed range
rng = parse_reference_range("135-145")
# -> {"low": 135.0, "high": 145.0, "low_inclusive": True, "high_inclusive": True}

derive_abnormal_flag(132, rng)            # "low"
derive_abnormal_flag(140, "135-145")      # "normal"  (raw range string accepted)
derive_abnormal_flag(150, "135 to 145")   # "high"

# One-sided bounds
derive_abnormal_flag(7, parse_reference_range("<5"))    # "high" (above the cap)
derive_abnormal_flag(3, parse_reference_range(">=10"))  # "low"

# Honor the lab's own explicit flag (takes precedence over derived comparison)
derive_abnormal_flag(132, "135-145", explicit_flag="C")   # "critical"
derive_abnormal_flag(132, "135-145", explicit_flag="HH")  # "critical"

# Unparseable / non-numeric inputs fail safe rather than guessing
derive_abnormal_flag("pending", "135-145")  # "unknown"
derive_abnormal_flag(132, "see report")     # "unknown"

print(LAB_FLAG_ADVISORY)  # surface this disclaimer with derived flags

AbnormalFlag is one of "low" | "normal" | "high" | "critical" | "unknown". ReferenceRange is a typed mapping of low, high, low_inclusive, high_inclusive.

Workflow

1. Get value + range + (optional) lab flag from extracted lab entities. The value should be numeric; the range may be a raw string or a parsed mapping.
2. Parse the reference range with parse_reference_range. It handles closed ranges ("135-145", "0.5 - 1.2", "135 to 145", en/em dashes) and one-sided bounds ("<5", "<=5", ">10", ">=10"). Contradictory or unparseable ranges return empty bounds rather than a guess — by design.
3. Derive the flag with derive_abnormal_flag(value, range, explicit_flag=). Resolution order: an explicit lab flag wins first (H/HIGH, L/LOW, C/CRIT/CRITICAL, HH/LL → critical, N/NORMAL); an unknown explicit flag returns "unknown" instead of being silently ignored. With no explicit flag, it compares the numeric value against the parsed bounds, respecting inclusive vs. exclusive edges.
4. Handle "unknown" explicitly. Non-numeric values, empty/unparseable ranges, or unrecognized explicit flags yield "unknown". Treat it as "needs review," not "normal."
5. Attach the advisory. Surface LAB_FLAG_ADVISORY wherever derived flags are shown — derived flags are heuristic and do not replace the originating laboratory's own diagnostic flagging.

Hand-off to / from OpenMed

• From extracting-clinical-entities: analyze_text lab/measurement entities give you the value text, unit, and often the reference range; this skill turns them into structured flags. Parse the numeric value out of the entity surface before calling derive_abnormal_flag.
• OpenMed calls: from openmed.clinical import parse_reference_range, derive_abnormal_flag, ReferenceRange, AbnormalFlag, LAB_FLAG_ADVISORY.
• To reconciling-problem-lists / FHIR grounding: a critical/high/low flag becomes a FHIR Observation.interpretation code (HL7 v3 ObservationInterpretation: H, L, HH, LL, N). Ground the LOINC code and UCUM unit out-of-process; OpenMed emits the flag, not the terminology binding.

Edge cases & gotchas

• Unit-agnostic — convert before comparing. The helpers ignore units entirely. If the value and the range are in different units (mg/dL vs mmol/L), the flag is wrong. Normalize units before calling, or only compare value and range that share a unit.
• Inclusive vs. exclusive edges. "<5" makes 5 the high bound exclusive; a value of exactly 5 flags high. parse_reference_range records high_inclusive=False for < and True for <= — respect it.
• Critical needs an explicit flag. Derived comparison yields only low/normal/ high. "critical" comes from the lab's explicit flag (C, HH, LL); the helpers do not infer critical thresholds beyond the reference range.
• Empty bounds are intentional. A range with both bounds missing returns "unknown" from derive_abnormal_flag, not "normal". Don't treat unknown as in-range.
• Local-first, advisory-only. Runs on-device; flags are decision support, not a diagnosis. Always carry LAB_FLAG_ADVISORY.

Standards & references

• LOINC — universal codes for laboratory observations: https://loinc.org/
• UCUM — Unified Code for Units of Measure: https://ucum.org/
• HL7 v3 ObservationInterpretation (H/L/HH/LL/N abnormal flags): https://terminology.hl7.org/CodeSystem-v3-ObservationInterpretation.html
• HL7 FHIR R4 Observation — referenceRange and interpretation: https://hl7.org/fhir/R4/observation.html