In a 27-year-old male with known aplastic anemia presenting with abdominal pain, weakness, pallor, pancytopenia, acute kidney injury (AKI) with severe azotemia, hypertension, metabolic acidosis, indirect hyperbilirubinemia, elevated lactate dehydrogenase (LDH), normal coagulation profile, negative Coombs test, and normal renal ultrasound, what is the complete diagnosis and management according to Harrison and Philippine guidelines, which diagnostic studies are lacking, and how should the orders and SOAP note be documented in the chart?

Diagnosis: Atypical Hemolytic Uremic Syndrome (aHUS) Complicating Aplastic Anemia

This patient has atypical hemolytic uremic syndrome (aHUS), a complement-mediated thrombotic microangiopathy (TMA), superimposed on his known aplastic anemia, and requires urgent ADAMTS13 testing, peripheral blood smear for schistocytes, haptoglobin level, stool culture for VTEC, and immediate consideration of complement blockade therapy with eculizumab or ravulizumab.

Clinical Reasoning

Why This is aHUS and Not Just Aplastic Anemia Progression

The clinical presentation demonstrates the classic triad of TMA: 1

• Microangiopathic hemolytic anemia: Indirect hyperbilirubinemia, elevated LDH (1041), negative Coombs test (excluding immune hemolysis) 1
• Thrombocytopenia: Part of the pancytopenia picture with platelet consumption 1
• Acute kidney injury: Severe progressive azotemia (creatinine 484.5→698.66 µmol/L despite dialysis), normal kidney size/structure on ultrasound, hypertension 1

The key distinguishing features from simple aplastic anemia progression include: 1

• Acute, severe renal failure with normal kidney architecture (aplastic anemia alone does not cause AKI)
• Indirect hyperbilirubinemia indicating hemolysis (not typical of aplastic anemia)
• Markedly elevated LDH suggesting ongoing cell destruction
• Metabolic acidosis and hypertension consistent with TMA-related renal injury
• Failure to respond to supportive care and dialysis

Differential Diagnosis Considerations

Must urgently exclude: 1

• Thrombotic thrombocytopenic purpura (TTP): Requires ADAMTS13 activity level (severely deficient <10 IU/dL in TTP)
• STEC-HUS: Requires stool culture for verocytotoxin-producing E. coli (VTEC)
• Secondary TMA: Drug-induced, infection-related, or malignancy-associated

The absence of diarrhea, normal coagulation studies (excluding DIC), and clinical context strongly favor aHUS over STEC-HUS. 1

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Lacking Diagnostic Studies (URGENT)

First-Level Tests (Order STAT): 1

1. ADAMTS13 activity level - Must be drawn BEFORE any plasma therapy; distinguishes TTP from aHUS 1
2. Peripheral blood smear - Evaluate for schistocytes (>1% supports TMA, but absence does not exclude it) 1
3. Haptoglobin level - Should be reduced in hemolysis 1
4. Stool culture for VTEC/Shiga toxin - Exclude STEC-HUS 1
5. Reticulocyte count - Assess bone marrow response to hemolysis
6. Urinalysis with microscopy - Document hematuria/proteinuria 1
7. Complete metabolic panel with calcium, phosphate, uric acid - Assess tumor lysis and metabolic derangements

Second-Level Tests (Send Within 24-48 Hours): 1

1. Complement studies: C3, C4, CH50, factor H, factor I levels
2. Genetic testing for complement pathway mutations - CFH, CFI, CFB, C3, MCP, THBD genes (especially important given young age)
3. Anti-factor H antibodies - Can cause acquired aHUS
4. Cobalamin (B12) and methylmalonic acid levels - Exclude MMACHC-related HUS 1
5. Repeat bone marrow biopsy with cytogenetics and molecular studies - Exclude hypoplastic MDS, clonal evolution, or inherited bone marrow failure syndromes (IBMFS) 2, 3

Additional Considerations:

1. Blood cultures - Given immunocompromised state from aplastic anemia 2
2. Viral serologies - CMV, EBV, HIV, parvovirus B19 (can trigger TMA or worsen aplastic anemia)
3. Pregnancy test (if applicable) - Pregnancy-associated TMA is a consideration

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Management Algorithm

Immediate Management (Within Hours):

1. Supportive Care: 2, 4

• Continue hemodialysis for uremia and metabolic acidosis (sodium bicarbonate infusion does NOT improve mortality in severe metabolic acidemia with AKI per recent RCT) 5
• Strict blood pressure control (target <140/90 mmHg) - use calcium channel blockers or ACE inhibitors cautiously
• Transfuse packed RBCs to maintain Hgb >7 g/dL; platelets if <10,000/µL or active bleeding 2
• Antimicrobial prophylaxis (fluoroquinolone or azole antifungal) given aplastic anemia 2

2. Hold Nephrotoxic Agents:

• Discontinue any potential TMA-triggering medications
• Avoid calcineurin inhibitors (cyclosporine) if previously used for aplastic anemia until aHUS excluded

3. Do NOT Start Plasma Exchange (PLEX) Until ADAMTS13 Results Available:

• If ADAMTS13 <10%, this is TTP → start daily PLEX immediately
• If ADAMTS13 >10%, this is likely aHUS → PLEX is NOT effective and delays definitive therapy 1

Definitive Therapy for aHUS (Once TTP Excluded):

4. Complement Blockade - First-Line Therapy: 1

Eculizumab (preferred) or Ravulizumab:

• MUST vaccinate against Neisseria meningitidis (quadrivalent conjugate vaccine + serogroup B vaccine) at least 2 weeks before starting therapy if possible; if urgent, give prophylactic antibiotics (penicillin or macrolide) for duration of therapy 1
• Eculizumab dosing: 900 mg IV weekly × 4 weeks, then 1200 mg at week 5, then 1200 mg every 2 weeks maintenance 1
• Ravulizumab dosing (alternative): Weight-based loading dose followed by maintenance every 8 weeks 1
• Monitor for treatment response: platelet count recovery, LDH normalization, creatinine improvement within 1-2 weeks 1

5. Hematology Consultation:

• Coordinate care between nephrology and hematology given dual diagnosis of aplastic anemia and aHUS
• Discuss long-term immunosuppressive therapy (IST) for aplastic anemia once aHUS stabilized 2, 4
• Consider allogeneic hematopoietic stem cell transplant (HSCT) evaluation if matched sibling donor available (curative for aplastic anemia in patients <50 years) 2, 4

Common Pitfalls to Avoid:

• Do NOT delay ADAMTS13 testing - this is the critical branch point in management 1
• Do NOT assume this is just aplastic anemia progression - AKI with hemolysis requires TMA workup 1
• Do NOT start PLEX empirically - ineffective for aHUS and delays complement blockade 1
• Do NOT forget meningococcal vaccination/prophylaxis before complement blockade - life-threatening risk 1
• Absence of schistocytes does NOT exclude TMA - low sensitivity of peripheral smear 1

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SOAP Note Documentation

SUBJECTIVE:

27-year-old male with known aplastic anemia (diagnosed [DATE]) presenting with 3-day history of abdominal pain, progressive weakness, and pallor. Denies diarrhea, bloody stools, recent infections, new medications, or sick contacts. No neurological symptoms (headache, vision changes, seizures, confusion).

OBJECTIVE:

Vital Signs:

• BP: Elevated (document specific values) - hypertensive episodes noted
• Other vitals: [Document HR, RR, Temp, O2 sat]

Physical Exam:

• General: Pallor, weakness
• Cardiovascular: [Document findings]
• Abdomen: Tenderness (document location/severity), no peritoneal signs
• Neurological: Alert, oriented, no focal deficits, no seizures
• Skin: No petechiae, purpura, or rash noted

Laboratory Data:

Renal Function:

• Creatinine: 613→972→646→873→484.5 (post-HD)→698.66 µmol/L (78.8 mg/dL)
• BUN: Elevated (document value)
• Urine output: [Document]

Hematology:

• CBC: Pancytopenia (document specific values for WBC, Hgb, Plt)
• LDH: 1041 U/L (markedly elevated)
• Indirect bilirubin: Elevated (document value)
• Direct and indirect Coombs: Negative
• D-dimer: 5 (document units)

Coagulation:

• PT/INR: Normal
• aPTT: Normal

Chemistry:

• AST: Elevated (document value)
• ABG: Metabolic acidosis (document pH, HCO3, pCO2, lactate)

Infectious:

• HBsAg: Non-reactive
• Leptospirosis workup: [Document results]

Imaging:

• Whole abdomen ultrasound: Normal liver, spleen, pancreas; kidneys normal size with preserved cortical thickness; no hydronephrosis, obstruction, mass, or lithiasis

ASSESSMENT:

Primary Diagnosis:

1. Atypical Hemolytic Uremic Syndrome (aHUS) - Complement-Mediated Thrombotic Microangiopathy 1
   • Classic triad present: microangiopathic hemolytic anemia (elevated LDH, indirect hyperbilirubinemia, negative Coombs), thrombocytopenia, acute kidney injury
   • Severe progressive AKI despite dialysis with normal renal architecture
   • ADAMTS13 pending to exclude TTP
   • VTEC stool culture pending to exclude STEC-HUS

Secondary Diagnosis: 2. Aplastic Anemia - Known diagnosis, contributing to baseline pancytopenia 2, 3

Complications: 3. Acute Kidney Injury, Stage 3 (KDIGO) - Requiring hemodialysis 1 4. Severe Metabolic Acidosis - Secondary to AKI 5 5. Hypertension - Secondary to TMA-related renal injury 1

Differential Diagnoses (Being Excluded):

• Thrombotic thrombocytopenic purpura (TTP) - ADAMTS13 pending
• STEC-HUS - Stool VTEC pending; no diarrhea makes less likely
• Drug-induced TMA - Review medication history
• Sepsis with DIC - Normal coagulation studies argue against
• Hypoplastic MDS - Requires bone marrow re-evaluation

PLAN:

Diagnostic:

1. STAT Labs:

   • ADAMTS13 activity level (CRITICAL - drawn before any plasma therapy)
   • Peripheral blood smear for schistocyte count
   • Haptoglobin level
   • Stool culture for VTEC/Shiga toxin
   • Reticulocyte count
   • Urinalysis with microscopy
   • Repeat CMP with calcium, phosphate, uric acid

2. Send Today:

   • Complement studies: C3, C4, CH50, factor H, factor I
   • Anti-factor H antibodies
   • Cobalamin (B12) and methylmalonic acid levels
   • Blood cultures × 2 sets
   • Viral serologies: CMV, EBV, HIV, parvovirus B19

3. Coordinate Within 48 Hours:

   • Genetic testing for complement pathway mutations (CFH, CFI, CFB, C3, MCP, THBD)
   • Repeat bone marrow biopsy with cytogenetics and molecular studies to exclude clonal evolution/MDS

Therapeutic:

Immediate (Today):

1. Continue hemodialysis as scheduled for uremia and volume management
2. Blood pressure control: Start amlodipine 5 mg PO daily (avoid ACEi until renal function stabilizes)
3. Transfusion support:
   • pRBC transfusion if Hgb <7 g/dL
   • Platelet transfusion if <10,000/µL or active bleeding
4. Antimicrobial prophylaxis: Continue current regimen for aplastic anemia (document specific agents)
5. Hold nephrotoxic medications: Review and discontinue any potential TMA triggers
6. NPO except medications until abdominal pain etiology clarified

Pending ADAMTS13 Results:

• If ADAMTS13 <10%: Initiate daily plasma exchange for TTP
• If ADAMTS13 >10%: Proceed with complement blockade for aHUS (see below)

Definitive Therapy for aHUS (Once TTP Excluded):

1. Meningococcal vaccination:

   • Administer MenACWY and MenB vaccines TODAY
   • Start prophylactic penicillin VK 500 mg PO BID (or azithromycin 250 mg PO daily if PCN allergic) until 2 weeks post-vaccination, then continue throughout complement blockade therapy

2. Eculizumab therapy (coordinate with pharmacy/hematology):

   • Loading: 900 mg IV weekly × 4 weeks
   • Week 5: 1200 mg IV
   • Maintenance: 1200 mg IV every 2 weeks
   • Monitor: CBC, CMP, LDH weekly initially; assess platelet recovery and creatinine improvement

Consultations:

1. Nephrology - Actively involved; continue dialysis management
2. Hematology - STAT consult for aHUS/TMA management and aplastic anemia coordination
3. Pharmacy - Eculizumab procurement and dosing verification
4. Infectious Disease - Consider consult for antimicrobial management in immunocompromised patient

Monitoring:

• Telemetry for hypertensive episodes
• Strict I/O monitoring
• Daily CBC, CMP, LDH
• Neurological checks Q4H (watch for TMA-related neurological complications: seizures, encephalopathy, vision changes) 1
• Daily weights

Disposition:

• ICU-level care given severe AKI requiring dialysis, metabolic acidosis, and potential for rapid decompensation
• Family meeting to discuss diagnosis, prognosis, and treatment plan including need for complement blockade therapy

Code Status: [Document]

Follow-Up:

• Reassess after ADAMTS13 results available (expected within 24-48 hours)
• Hematology to discuss long-term aplastic anemia management (IST vs. HSCT evaluation) once aHUS stabilized
• Genetic counseling once complement mutation testing results available

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Key Documentation Points for Chart Orders:

STAT Orders:

• ADAMTS13 activity (send to reference lab, call for expedited processing)
• Peripheral blood smear with schistocyte count
• Haptoglobin
• Stool culture for VTEC/Shiga toxin
• Reticulocyte count
• Urinalysis with microscopy
• Meningococcal vaccines (MenACWY + MenB) - administer TODAY
• Penicillin VK 500 mg PO BID (start immediately)

Routine Orders:

• Complement panel (C3, C4, CH50, factor H, factor I, anti-factor H antibodies)
• Cobalamin and methylmalonic acid
• Blood cultures × 2
• Viral serologies panel
• Amlodipine 5 mg PO daily
• Continue current transfusion thresholds and antimicrobial prophylaxis
• Telemetry monitoring
• Neurological checks Q4H
• Daily labs: CBC, CMP, LDH

Pending Orders (Activate When ADAMTS13 >10%):

• Eculizumab 900 mg IV infusion over 35 minutes (premedicate with acetaminophen 650 mg PO)
• Genetic testing panel for complement mutations (coordinate with hematology)