# ICU/CTICU worked laboratory examples
> **Educational work by a pre-medical student — not medical advice.** Not a clinical protocol, prescription, or patient handout, and not for patient care. See [DISCLAIMER](DISCLAIMER.md).
**Evidence labels:** [Guideline/consensus recommendation](EVIDENCE_CLASSIFICATION.md#recommendations) (strength and population stated), **general clinical knowledge**, **context-dependent clinical practice**, and **synthetic example**. A case or original diagram is not a standardized treatment protocol.
28 October 2026. These 11 worked examples extend the [18 procedure pairs](CTICU_PROCEDURE_EXAMPLES.md) and [42 integrated ICU topics](ICU_CTICU_WORKUP_CASES.md). Paired-case context lines name the matching procedure-casebook example; where an example is not one of the 18 pairs, it is labeled as an additional synthetic example. People, numerical results and trends are wholly synthetic; no clinical outcome is claimed. These are explanations of source-supported clinical reasoning, not quizzes or an order set.
Choose an investigation to answer a clinical question that may change care. Review prior results, specimen/site, timing, current support, exposures and local assay ranges. A result supports or challenges a diagnosis; it does not independently diagnose every cause or prescribe treatment. Urgent assessment and treatment can proceed in parallel with investigation. Frequency depends on instability and the decision at hand.
## Postoperative bleeding and anemia
**Paired case context — synthetic example:** The coronary-bypass male example has a new fall in pressure, which raises a postoperative bleeding question among other causes; the endovascular aortic-repair female example develops new pain and a falling pressure.
**Investigation and purpose — context-dependent clinical practice:** CBC (hemoglobin/hematocrit and platelets); fibrinogen and appropriate coagulation studies if bleeding is clinically suspected. Compatibility testing is considered when transfusion may be needed.
**Illustrative finding — synthetic data / clinical interpretation:** A fictional hemoglobin decrease from 10 to 8 g/dL, interpreted with timing, dilution, drain losses and perfusion, raises an anemia/blood-loss question. It is not a transfusion threshold.
**Effect on care — context-dependent clinical practice:** The team evaluates a surgical source and clinically relevant coagulopathy; selected viscoelastic testing can help guide a local hemostatic pathway. A laboratory result cannot exclude tamponade or replace surgical review.
**Classification note:** General clinical knowledge and context-dependent bleeding assessment; the fictional hemoglobin change is not a standardized transfusion trigger. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [PBM](https://pmc.ncbi.nlm.nih.gov/articles/PMC12257489/).
## Carbon dioxide retention and acidemia
**Paired case context — synthetic example:** The ARDS female example develops hypercapnia and ventilator dyssynchrony; the coronary-bypass male example has shallow breathing with incisional pain, so analgesic exposure is also reviewed.
**Investigation and purpose — context-dependent clinical practice:** Arterial blood gas with documented oxygen/support conditions, interpreted alongside examination and delivered ventilation.
**Illustrative finding — synthetic data / clinical interpretation:** Fictional pH 7.28, PaCO2 60 mmHg and bicarbonate 27 mmol/L demonstrate acidemia with a respiratory component; baseline and other data are needed for acute/chronic or mixed classification.
**Effect on care — context-dependent clinical practice:** The team reviews airway patency, minute ventilation, mechanics and medication effects. Raising FiO2 alone does not correct inadequate ventilation. Sampling error or a venous sample changes interpretation.
**Classification note:** General clinical knowledge plus synthetic numerical interpretation; this is not a guideline-defined intubation or ventilator-adjustment threshold. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [GAS](https://www.aarc.org/wp-content/uploads/2025/03/davis-et-al-2013-aarc-clinical-practice-guideline-blood-gas-analysis-and-hemoximetry-2013.pdf), [VENTASSESS](https://pmc.ncbi.nlm.nih.gov/articles/PMC11298231/).
## Oxygenation under defined support
**Paired case context — synthetic example:** The male severe-pneumonia/ARDS example has worsening oxygenation; the female single-lung-transplant example develops hypoxemia with altered airway pressures.
**Investigation and purpose — context-dependent clinical practice:** An arterial gas when it can resolve the oxygenation question, with FiO2, PEEP/support and sample time recorded.
**Illustrative finding — synthetic data / clinical interpretation:** PaO2 80 mmHg on FiO2 0.50 gives a P:F ratio of 160 mmHg. This calculation alone does not diagnose ARDS or graft dysfunction.
**Effect on care — context-dependent clinical practice:** The team combines the finding with imaging, timing and competing cardiac/fluid/airway causes, then reassesses support and the underlying cause. A different support condition makes a serial ratio less comparable.
**Classification note:** General clinical knowledge/arithmetic; the P:F calculation is not a complete diagnostic criterion or treatment instruction. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [GAS](https://www.aarc.org/wp-content/uploads/2025/03/davis-et-al-2013-aarc-clinical-practice-guideline-blood-gas-analysis-and-hemoximetry-2013.pdf), [ARDS](https://pmc.ncbi.nlm.nih.gov/articles/PMC10870893/).
## Lactate in sepsis or postoperative shock
**Paired case context — synthetic example:** The esophagectomy female example has fever and hypotension, raising a sepsis question; the VA-ECMO male example has cool extremities and a rising lactate despite displayed circuit flow.
**Investigation and purpose — context-dependent clinical practice:** Lactate when shock/sepsis evaluation calls for it, alongside pressure, examination, urine output and cardiac/source assessment.
**Illustrative finding — synthetic data / clinical interpretation:** A fictional lactate trend from 4 to 3 mmol/L is one improving measurement, not proof that shock has resolved. Production, clearance and treatments affect the value.
**Effect on care — context-dependent clinical practice:** The team reassesses perfusion and the cause. Persistent elevation does not automatically mandate more fluid, particularly when congestion or respiratory deterioration is present.
**Classification note:** Guideline recommendation G24 is conditional (low certainty) for measuring lactate in sepsis; interpretation and response in this case are context-dependent. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [SEPSIS](https://sccm.org/clinical-resources/guidelines/guidelines/surviving-sepsis-campaign-international-guidelines-for-management-of-sepsis-and-septic-shock-2026), [HEMO](https://pmc.ncbi.nlm.nih.gov/articles/PMC10175734/), [SHOCK25](https://link.springer.com/article/10.1007/s00134-025-08137-z).
## Kidney injury after major surgery
**Paired case context — synthetic example:** The open AAA-repair male example has abdominal distension and reduced urine output; the arch-repair female example has reduced urine output with a focal neurological change. The heart-transplant male example (low output with worsening kidney function) adds a medication-exposure question.
**Investigation and purpose — context-dependent clinical practice:** Creatinine/BUN, electrolytes and relevant acid-base measures, urine-output/balance trends; urinalysis or imaging when a specific cause is being evaluated.
**Illustrative finding — synthetic data / clinical interpretation:** A fictional creatinine rise from 1.0 to 1.6 mg/dL within 48 hours is compatible with an AKI creatinine criterion after measurement/context checks. It does not identify the cause.
**Effect on care — context-dependent clinical practice:** Assessment distinguishes perfusion, congestion, obstruction and renal injury/exposure. Dialysis is considered from clinical needs and trajectory, not this creatinine value alone.
**Classification note:** Guideline diagnostic definition G25 is not graded. The fictional creatinine change fits a definition component after context checks; the cause and management remain clinical assessments. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [AKI](https://kdigo.org/wp-content/uploads/2016/10/KDIGO-2012-AKI-Guideline-English.pdf), [RRT](https://kdigo.org/wp-content/uploads/2016/10/KDIGO-2012-AKI-Guideline-English.pdf). KDIGO 2012 remains the final published guideline; a 2026 KDIGO AKI/AKD update was in public-review draft at the time of writing and is not used here as final guidance.
## Potassium and rhythm/perfusion changes
**Paired case context — synthetic example:** The mechanical aortic-valve male example develops bradycardia and reduced urine output; the limb-revascularization male example has increasing pain, tense swelling and sensory change after reperfusion, a setting in which potassium release and kidney injury are also considered.
**Investigation and purpose — context-dependent clinical practice:** Potassium and renal/acid-base chemistry; magnesium where the rhythm or exposure question makes it relevant, with ECG/clinical assessment.
**Illustrative finding — synthetic data / clinical interpretation:** A fictional potassium result of 6.2 mmol/L raises an urgent hyperkalemia concern. Sample hemolysis can mislead; confirmation is coordinated without delaying necessary treatment of a clinically dangerous presentation.
**Effect on care — context-dependent clinical practice:** The clinical team assesses electrical effects, medications, kidney function and the need for correction or renal support. This example is not a universal treatment threshold or replacement dose.
**Classification note:** General clinical knowledge and context-dependent urgent assessment. The fictional potassium value is not asserted to be one universal treatment threshold. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [RRT](https://kdigo.org/wp-content/uploads/2016/10/KDIGO-2012-AKI-Guideline-English.pdf), [HEMO](https://pmc.ncbi.nlm.nih.gov/articles/PMC10175734/).
## New fever and a suspected source
**Paired case context — synthetic example:** The esophagectomy female example has shock with altered drain findings; the male pneumonia example has compatible respiratory findings.
**Investigation and purpose — context-dependent clinical practice:** Blood cultures in suspected sepsis and source-directed microbiology; respiratory sampling or other studies only when clinically indicated.
**Illustrative finding — synthetic data / clinical interpretation:** A positive culture must be interpreted for pathogen, collection quality, contamination, source and prior therapy. A white count alone neither proves nor excludes infection.
**Effect on care — context-dependent clinical practice:** Results help refine antimicrobial/source management. Sampling should not harmfully delay time-critical treatment. The general new-fever guideline excludes severe immunocompromise; transplant investigation follows the transplant service plan.
**Classification note:** Guideline recommendation G23 is strong (low certainty) for blood cultures in the stated sepsis population. Other source-directed investigations remain context-dependent; general fever guidance excludes severe immunocompromise. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [FEVER](https://www.idsociety.org/practice-guideline/new-fever-in-critically-ill-patients/), [SEPSIS](https://sccm.org/clinical-resources/guidelines/guidelines/surviving-sepsis-campaign-international-guidelines-for-management-of-sepsis-and-septic-shock-2026).
## Bleeding/thrombosis balance with anticoagulation
**Paired case context — synthetic example:** The mechanical aortic-valve male example and the female LVAD or Impella examples receive different anticoagulant therapies.
**Investigation and purpose — context-dependent clinical practice:** The assay appropriate to the actual agent and indication, such as INR for vitamin-K antagonist effect, or a protocol-defined aPTT/anti-Xa assessment for heparin. CBC and clinical bleeding/device findings add context.
**Illustrative finding — synthetic data / clinical interpretation:** An INR result cannot be treated as the effect of every anticoagulant. Results depend on medication, assay, timing and clinical context.
**Effect on care — context-dependent clinical practice:** The team evaluates bleeding and thrombotic risk before adjusting therapy under the actual valve/device plan. No common target can be assigned to both examples.
**Classification note:** General clinical knowledge and drug/device-specific practice; there is no universal assay or target across these therapies. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [PBM](https://pmc.ncbi.nlm.nih.gov/articles/PMC12257489/), [MCS](https://pmc.ncbi.nlm.nih.gov/articles/PMC12524590/).
## Anemia or dark urine during mechanical support
**Paired case context — synthetic example:** The established-LVAD female example has alarms, dark urine and a falling hemoglobin; the Impella female example has dark urine and a falling hemoglobin. The Impella male example has access-site swelling, so blood loss must be distinguished from hemolysis.
**Investigation and purpose — context-dependent clinical practice:** CBC, renal chemistry and selected hemolysis measures, such as plasma-free hemoglobin, LDH, bilirubin or haptoglobin, interpreted with device/imaging findings.
**Illustrative finding — synthetic data / clinical interpretation:** A rising LDH alone does not establish pump thrombosis. Hemolysis, blood loss and other tissue injury must be distinguished.
**Effect on care — context-dependent clinical practice:** The support team evaluates position, loading, circuit/device problems and patient effects. No speed or anticoagulant change is selected from one result.
**Classification note:** General clinical knowledge and specialist practice; no isolated marker establishes pump thrombosis. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [MCS](https://pmc.ncbi.nlm.nih.gov/articles/PMC12524590/), [LVAD](https://www.mdpi.com/2077-0383/11/9/2575).
## Fluid, electrolyte and acid-base needs during CRRT
**Additional synthetic example (not one of the 18 procedure pairs):** A male with multiorgan failure remains fluid overloaded; a female with AKI has evolving acid-base/electrolyte abnormalities.
**Investigation and purpose — context-dependent clinical practice:** Chemistry and appropriate blood gas assessment, fluid balance and urine output; monitoring is tailored to modality, anticoagulant and clinical course.
**Illustrative finding — synthetic data / clinical interpretation:** Improved potassium or bicarbonate after treatment reflects part of the response, not kidney recovery by itself. Delivered therapy and ongoing losses matter.
**Effect on care — context-dependent clinical practice:** The renal/ICU team adjusts the prescription to patient needs and tolerance; fluid removal is balanced against perfusion. No fixed effluent, fluid-removal or laboratory interval is implied.
**Classification note:** Guideline statements G26 are not graded; CRRT preference in unstable patients (G27) is conditional, 2B. Monitoring and adjustment remain individualized. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [RRT](https://kdigo.org/wp-content/uploads/2016/10/KDIGO-2012-AKI-Guideline-English.pdf).
## A displayed number that conflicts with the patient
**Additional synthetic example (not one of the 18 procedure pairs):** A male with continuous-flow LVAD support has an unreliable pulse-oximetry signal; a female ventilated patient has an unexpected gas result.
**Investigation and purpose — context-dependent clinical practice:** Check measurement method, waveform/signal, specimen identity/site, timing and current support; use an appropriate independent assessment when necessary.
**Illustrative finding — synthetic data / clinical interpretation:** SpO2 estimates saturation; it does not measure PaCO2 or prove adequate ventilation. Low perfusion and other factors can impair accuracy.
**Effect on care — context-dependent clinical practice:** The team investigates the patient and the measurement together instead of escalating support solely from an unverified value. A blood gas addresses a specific unresolved question.
**Classification note:** General measurement knowledge and official device-safety information, applied to fictional observations. [Evidence details](EVIDENCE_CLASSIFICATION.md#laboratory-examples).
**Public clinical sources:** [SPO2](https://www.fda.gov/medical-devices/products-and-medical-procedures/pulse-oximeters), [GAS](https://www.aarc.org/wp-content/uploads/2025/03/davis-et-al-2013-aarc-clinical-practice-guideline-blood-gas-analysis-and-hemoximetry-2013.pdf), [LVAD](https://www.mdpi.com/2077-0383/11/9/2575).
## Source scope
The [public source register](CLINICAL_CARE_PUBLIC_SOURCES.md) identifies source type, DOI where applicable, support and review limits. The guideline recommendation is distinct from the fictional numbers and their authored application. Numerical findings are not society-approved cutoffs unless expressly identified as a diagnostic criterion. The earlier 20-category [investigation catalogue](ICU_CTICU_WORKUP_CASES.md) provides additional test-purpose/limitation explanations.