5 Liver, Pancreatic, Cardiac, and Blood Gas Results

Interpreting laboratory results

Laboratory results are clues, not diagnoses. Compare each result with the reporting laboratory’s reference interval, the patient’s baseline, symptoms, and trends. Reference ranges vary by laboratory, method, age, and other patient factors, so follow local critical-value policy.

Liver test patterns and response

Typical adult reference intervals are approximate and should be compared with the laboratory’s own ranges.

• ALT: About $4\text{–}40\ \mathrm{U/L}$. Elevation suggests hepatocellular injury; ALT is relatively liver-specific.

• AST: About $8\text{–}40\ \mathrm{U/L}$. Elevation may reflect liver injury, but AST also comes from muscle and other tissues.

• ALP: About $20\text{–}130\ \mathrm{U/L}$. Elevation may indicate cholestasis or bile-duct obstruction; bone disease can also raise it.

• Total bilirubin: About $0.1\text{–}1.2\ \mathrm{mg/dL}$. Elevation can cause jaundice and may reflect impaired processing or bile flow, or increased red-cell breakdown.

• Albumin: About $3.4\text{–}5.4\ \mathrm{g/dL}$. Low values may reflect reduced liver synthesis, but may also result from poor nutrition, inflammation, or protein loss.

• PT/INR: Use the laboratory interval. Without anticoagulants, INR is often about $0.8\text{–}1.2$. Prolongation may indicate impaired clotting-factor synthesis or vitamin K deficiency; consider medication effects.

ALT and AST mainly indicate cell injury, whereas bilirubin reflects processing and excretion. Albumin and PT/INR help assess liver synthetic function. A pattern with a prominent ALP rise suggests cholestasis; markedly elevated aminotransferases suggest hepatocellular injury. Interpret the pattern as a whole: an isolated abnormality does not establish a diagnosis.

Assess for jaundice, dark urine, pale stools, abdominal pain, bruising or bleeding, and mental-status change. Review medication and alcohol history as appropriate. Promptly report a rising INR, new bleeding, or confusion when liver dysfunction is suspected, and follow facility escalation procedures. Do not independently stop prescribed medicines based only on an abnormal panel.

Pancreatic enzymes

Common adult reference intervals are approximate and vary among laboratories.

• Lipase: Often $0\text{–}160\ \mathrm{U/L}$. Elevation may occur with pancreatitis or other pancreatic, biliary, intestinal, or renal conditions.

• Amylase: Often $40\text{–}140\ \mathrm{U/L}$. Elevation may occur with pancreatitis, but also with salivary-gland and other disorders.

Lipase is generally more useful than amylase when pancreatitis is suspected. Consider enzyme results alongside symptoms and other findings; an elevated enzyme alone does not prove pancreatitis.

For severe, persistent upper abdominal pain—especially with vomiting—assess pain, vital signs, hydration, and clinical status, then promptly notify the provider. Escalate hypotension, tachycardia, fever, respiratory distress, or worsening condition. Carry out ordered monitoring and treatment and follow local protocol.

Cardiac markers and urgent assessment

High-sensitivity cardiac troponin (hs-cTnI or hs-cTnT) is the preferred biomarker for myocardial injury. There is no single universal numeric cutoff: use the assay-specific upper reference limit, commonly the $99$th percentile. A rise or fall on serial measurements supports acute injury. A single elevated result indicates myocardial injury but does not by itself diagnose myocardial infarction (MI). Kidney disease, heart failure, sepsis, and pulmonary embolism can also elevate troponin.

CK-MB is less commonly used when troponin testing is available. Interpret cardiac markers with symptoms, ECG, and serial results; do not delay urgent assessment while awaiting repeat testing.

For chest discomfort or other symptoms concerning for acute coronary syndrome, rapidly assess the patient, obtain or assist with an ECG, initiate monitoring, and promptly notify the responsible clinician or activate the facility’s emergency pathway. Report a critical or rising troponin according to policy. Give oxygen only when indicated by hypoxemia or an applicable protocol or order. Document notifications and actions.

Arterial blood gas interpretation

Typical adult arterial values are approximate. Ranges and critical thresholds vary by laboratory and patient.

• pH: $7.35\text{–}7.45$, reflecting overall acidity or alkalinity.

• PaCO₂: $35\text{–}45\ \mathrm{mmHg}$, the respiratory acid; higher levels lower pH.

• HCO₃⁻: $22\text{–}26\ \mathrm{mEq/L}$, the metabolic base; lower levels lower pH.

• PaO₂: $80\text{–}100\ \mathrm{mmHg}$, reflecting arterial oxygenation; consider age and oxygen therapy.

• SaO₂: $95\text{–}100\%$, reflecting arterial oxygen saturation.

A PaO₂ below $60\ \mathrm{mmHg}$ is commonly considered critical. Use this quick interpretation sequence:

1. Check pH. Below $7.35$ indicates acidemia; above $7.45$ indicates alkalemia.

2. Identify the primary change. In a respiratory disorder, PaCO₂ moves opposite to pH. In a metabolic disorder, HCO₃⁻ moves in the same direction as pH.

3. Check compensation. The other system may partly or fully compensate. A normal pH does not rule out a compensated disorder.

4. Assess oxygenation and the patient. Interpret PaO₂ and SaO₂ alongside oxygen delivery, respiratory effort, mental status, and trends.

The examples show the primary interpretation:

• $\mathrm{pH}=7.30$, $\mathrm{PaCO_2}=50$, $\mathrm{HCO_3^-}=24$: low pH with high CO₂ indicates respiratory acidosis.

• $\mathrm{pH}=7.50$, $\mathrm{PaCO_2}=30$, $\mathrm{HCO_3^-}=24$: high pH with low CO₂ indicates respiratory alkalosis.

• $\mathrm{pH}=7.28$, $\mathrm{PaCO_2}=40$, $\mathrm{HCO_3^-}=18$: low pH with low bicarbonate indicates metabolic acidosis.

• $\mathrm{pH}=7.48$, $\mathrm{PaCO_2}=40$, $\mathrm{HCO_3^-}=30$: high pH with high bicarbonate indicates metabolic alkalosis.

Assess airway, breathing, circulation, mental status, respiratory effort, and oxygen-delivery equipment. For hypoxemia, severe acidemia or alkalemia, or clinical deterioration, promptly escalate care and initiate an emergency response when indicated. Apply oxygen or other interventions under orders and protocol, then reassess and report the response.

Applying results to clinical situations

Apply the laboratory pattern and the patient’s condition together; a result alone may not establish a diagnosis.

• A patient has yellow sclerae, total bilirubin of $4.0\ \mathrm{mg/dL}$, and elevated ALP. A cholestatic or bile-flow pattern is possible. Assess for jaundice, dark urine, pale stools, pain, and clinical deterioration; report the findings for evaluation.

• A patient with severe upper abdominal pain and vomiting has lipase markedly above the laboratory range. Assess vital signs, pain, hydration, and overall status; promptly notify the provider and escalate instability.

• A patient with chest pressure has hs-cTn above the assay’s $99$th-percentile limit. This establishes myocardial injury, not MI by itself. Rapidly assess, obtain or assist with ECG and monitoring, notify the clinician, and follow the serial-testing and emergency pathway.

• For $\mathrm{pH}=7.29$, $\mathrm{PaCO_2}=32\ \mathrm{mmHg}$, $\mathrm{HCO_3^-}=15\ \mathrm{mEq/L}$, and $\mathrm{PaO_2}=58\ \mathrm{mmHg}$, the primary findings are metabolic acidosis and low PaO₂ (hypoxemia). Immediately assess respiratory and hemodynamic status, verify oxygen delivery, and promptly escalate and report the critical findings.

Across these situations, assess the patient first when there are critical values or clinical deterioration, escalate promptly, follow protocol, and document.