What does reflexing refer to in relation to elevated lactate (lactic acid)?

What Does "Reflexing" Mean in Relation to Elevated Lactate?

"Reflexing" in the context of lactate testing refers to the automatic, protocol-driven follow-up testing that occurs when an initial lactate measurement exceeds a predefined threshold—typically ≥2 mmol/L or ≥4 mmol/L—triggering serial measurements every 2–6 hours to assess lactate clearance and guide resuscitation.

Core Concept of Lactate Reflexing

The term "reflex testing" describes an automated laboratory or clinical protocol where:

• Initial lactate ≥2 mmol/L indicates potential tissue hypoperfusion requiring investigation, and serial measurements are reflexively ordered to monitor trends 1
• Lactate ≥4 mmol/L represents a medical emergency with 46.1% mortality, mandating immediate protocolized resuscitation with repeat measurements every 2 hours during the first 6–8 hours 2, 1
• The goal is to achieve lactate clearance of ≥10% every 2 hours, with normalization to <2 mmol/L within 24 hours associated with 100% survival in trauma patients 2, 1

Why Serial Lactate Measurements Are "Reflexed"

Prognostic Significance Drives the Protocol

• Lactate clearance is more prognostically significant than absolute values—normalization within 24 hours associates with 100% survival, declining to 77.8% if normalized by 48 hours, and only 13.6% if lactate remains elevated beyond 48 hours 1, 3
• Serial measurements provide objective evaluation of response to therapy and are reliable prognostic indicators across all shock states 2, 1, 3
• The duration of lactic acidosis (time with lactate >2 mmol/L) is the best predictor of multi-organ failure development (R² = 0.266, P <0.001) 1

Clinical Decision Thresholds That Trigger Reflexing

Initial Lactate Level	Clinical Significance	Reflex Protocol	Citation
<2 mmol/L	Normal; no tissue hypoperfusion	No reflex testing needed	[1]
2–4 mmol/L	Moderate tissue hypoperfusion; ~30% mortality	Repeat every 2–6 hours; aggressive fluid resuscitation (≥30 mL/kg within 3 hours)	[2,1]
≥4 mmol/L	Severe tissue hypoperfusion; 46.1% mortality	Repeat every 2 hours during first 6–8 hours; immediate protocolized resuscitation	[2,1]

Practical Implementation of Lactate Reflexing

What Happens When Lactate Is "Reflexed"

• Automatic repeat orders are placed by the laboratory or clinical protocol without requiring a new physician order 1
• Target lactate clearance of ≥10–20% every 2 hours is monitored to assess adequacy of resuscitation 2, 1
• Resuscitation endpoints include MAP ≥65 mmHg, urine output ≥0.5 mL/kg/hr, CVP 8–12 mmHg, and ScvO₂ ≥70% in addition to lactate normalization 2, 1

Complementary Monitoring Alongside Reflexed Lactate

• Base deficit from arterial blood gas provides independent information about global tissue acidosis that doesn't strictly correlate with lactate, so both should be assessed 1, 3
• Clinical perfusion markers (capillary refill ≤2 seconds, warm extremities, normal mental status) should accompany lactate trends 1
• Central venous oxygen saturation (ScvO₂) may be misleading in sepsis—up to 23% of septic patients have lactate ≥2 mmol/L with ScvO₂ >70%, representing "cryptic shock" 1

Common Pitfalls in Lactate Reflexing Protocols

Don't Stop Reflexing Too Early

• A single normal lactate value does not guarantee sustained recovery—continued monitoring prevents premature de-escalation of care 1
• Even with lactate normalization, the precipitating condition (infection, hemorrhage, cardiac dysfunction) requires definitive treatment 1

Recognize Non-Hypoperfusion Causes

• Epinephrine can cause elevated lactate through beta-2-adrenergic receptor stimulation in skeletal muscle, activating glycogenolysis and glycolysis independent of tissue perfusion 1, 4
• Accelerated aerobic glycolysis driven by excess beta-adrenergic stimulation can increase lactate without tissue hypoxia 1, 4
• Alcohol consumption can confound interpretation—base deficit may be a more reliable marker than lactate in alcohol-associated presentations 1, 3

Specimen Type Matters for Reflexing Accuracy

• Plasma lactate is the gold standard for clinical decision-making because it reflects systemic lactate levels after cellular components are removed 1, 3
• Whole blood lactate measurements are typically 10–15% higher than plasma lactate because red blood cells contain lactate 1
• Don't assume whole blood and plasma lactate are interchangeable—the 10–15% difference can affect clinical thresholds, particularly when values are near decision points like 2 or 4 mmol/L 1

Clinical Algorithm for Lactate Reflexing

Step 1: Initial Lactate Measurement

• Measure lactate in all patients with suspected sepsis, shock, trauma, or tissue hypoperfusion 2, 1

Step 2: Interpret and Initiate Reflex Protocol

• Lactate <2 mmol/L: No reflex testing; reassess clinically 1
• Lactate 2–4 mmol/L: Begin aggressive fluid resuscitation; repeat lactate every 2–6 hours 2, 1
• Lactate ≥4 mmol/L: Initiate protocolized resuscitation immediately; repeat lactate every 2 hours during first 6–8 hours 2, 1

Step 3: Monitor Lactate Clearance

• Target ≥10% reduction every 2 hours 2, 1
• If lactate clearance <10% every 2 hours during the first 8 hours, this indicates ongoing tissue hypoperfusion requiring escalation of therapy 1

Step 4: Assess for Normalization

• Normalization to <2 mmol/L within 24 hours is the goal 1, 3
• Lactate >2 mmol/L persisting >6 hours is associated with significantly increased mortality 1

Step 5: Continue Reflexing Until Sustained Normalization

• Don't stop serial measurements after a single normal value—ensure sustained recovery 1