From the Guidelines
Hemolytic uremic syndrome (HUS) is characterized by laboratory findings including thrombocytopenia, microangiopathic hemolytic anemia with schistocytes on peripheral blood smear, and acute kidney injury, as evidenced by the most recent guidelines 1. The key lab findings in HUS include:
- Thrombocytopenia (low platelet count)
- Microangiopathic hemolytic anemia (with schistocytes on peripheral blood smear) 1
- Acute kidney injury (elevated creatinine and BUN) 1 Additional laboratory findings often include:
- Elevated lactate dehydrogenase (LDH)
- Decreased haptoglobin
- Elevated reticulocyte count
- Negative Coombs test In typical HUS (associated with Shiga toxin-producing E. coli), stool cultures may be positive for E. coli O157:H7 or other Shiga toxin-producing strains 1. Urinalysis typically shows hematuria and proteinuria. In atypical HUS, complement studies may reveal abnormalities in the alternative complement pathway 1. Coagulation studies are generally normal, which helps distinguish HUS from disseminated intravascular coagulation (DIC) 1. These laboratory findings reflect the underlying pathophysiology of HUS, which involves endothelial damage, platelet activation, and formation of microthrombi in small vessels, particularly in the kidneys, leading to organ damage. Frequent monitoring of hemoglobin and platelet counts, electrolytes, and blood urea nitrogen and creatinine is recommended to detect hematologic and renal function abnormalities that are early manifestations of HUS 1. Examining a peripheral blood smear for the presence of red blood cell fragmentation is necessary when HUS is suspected 1.
The diagnostic work-up for HUS should include a comprehensive evaluation, including history and physical examination, CBC with indices, blood smear morphology, serum creatinine, ADAMTS13, homocysteine/methylmalonic acid, complement testing, and evaluation of reticulocyte count and mean corpuscular volume 1. It is also important to evaluate for infectious causes, including screening for Epstein-Barr virus (EBV), CMV, human herpesvirus 6, and to evaluate for nutritional causes of macrocytosis (B12 and folate) 1. Additionally, evaluation for diarrheal causes, shiga toxin, Escherichia coli 0157, and common drugs causing hemolysis should be considered 1. Direct antibody test (Coombs test), haptoglobin, LDH, and other etiologies of anemia should also be evaluated 1.
Overall, the laboratory findings in HUS are critical for diagnosis and management, and a comprehensive diagnostic work-up is essential to identify the underlying cause and to guide treatment. The most recent guidelines recommend a thorough evaluation, including laboratory tests and imaging studies, to diagnose and manage HUS 1.
From the FDA Drug Label
Baseline platelet count (× 109/L), median (range)125 (16 – 332) Baseline LDH (U/L), median (range)375 (131 – 3318)
The lab findings for Hemolytic Uremic Syndrome (HUS) include:
- Low platelet count: median 125 × 10^9/L (range 16-332 × 10^9/L)
- Elevated LDH: median 375 U/L (range 131-3318 U/L) 2
From the Research
Lab Findings for Hemolytic Uremic Syndrome (HUS)
The lab findings for HUS include:
- Thrombocytopenia and microangiopathic hemolytic anemia, which are the hallmark of the thrombotic microangiopathies (TMAs) 3
- Hemolytic anemia with schistocytes, thrombocytopenia without evidence of disseminated intravascular coagulation, and renal failure 4
- Elevated lactate dehydrogenase, low haptoglobin, and low hemoglobin, plus thrombocytopenia and accompanying signs and symptoms of organ system involvement 5
- Red cell distribution width (RDW), platelets, and hemoglobin levels can be used to monitor the disease 6
Diagnostic Tests
Diagnostic tests for HUS include:
- Measurement of ADAMTS13, which can diagnose accurately the majority of TTP cases and distinguish it from atypical HUS 3, 5
- Platelet count and serum creatinine, which can predict the deficiency of the protease with a good degree of accuracy 3
- Tests to demonstrate the activation of the complement system, which can help to tailor the short- and long-term treatment with eculizumab 3
Biomarkers
Biomarkers for HUS include: