July 2026 Research Update

Across these reports, the common message is that atypical hemolytic uremic syndrome (aHUS) and related complement-driven clotting-in-small-blood-vessels problems can appear during or after a major stressor, and can look like other conditions at first. Even when the trigger is addressed (for example, blood pressure brought under control or an infection treated), the blood and kidney problems may not improve as expected or may come back, which raised suspicion for a complement-driven process in these cases. [1] [2] [3] [4] [5]

Several papers focused on pregnancy-related situations. One clinical article discussed complement-mediated thrombotic microangiopathy (TMA) triggered by pregnancy and described how bedside features such as the severity and speed of kidney injury, and lack of improvement with trigger-focused care, influenced concern for a complement-driven TMA. [1] A separate postpartum case report described a woman who developed low platelets, red blood cell breakdown, and acute kidney injury after delivery, with normal ADAMTS13 testing and an elevated complement activation marker (sC5b-9). [4]

Severe (malignant) high blood pressure was highlighted as another potential trigger where the picture can be confusing. In one case, a young man had malignant hypertension along with lung bleeding and kidney failure that came back even after blood pressure was stabilized, alongside low C3 (a complement blood protein), and he later improved after complement-blocking treatment. [2]

Transplantation was also described as a triggering setting. One liver transplant recipient developed complement-mediated TMA after transplant and had rapid blood count and kidney recovery after plasma exchange followed by complement-blocking treatment, with no relapse reported during 12 months of follow-up. [3] Separately, an influenza A case showed how a similar picture can have a different cause: a 21-year-old man had TMA with normal ADAMTS13 testing that the authors attributed to the flu itself (secondary TMA) rather than to aHUS. Some complement markers were raised, but the pattern expected in aHUS was not present, and his blood counts recovered after plasma exchange and high-dose steroids. [6]

These reports also showed how overlapping causes can complicate the picture. An infant initially diagnosed with Shiga toxin-producing E. coli-associated hemolytic uremic syndrome (STEC-HUS) later had an unusual drop in platelets during recovery, prompting reconsideration for atypical HUS and complement testing; the child improved after complement-blocking treatment but relapsed months later. [5] A separate clinical article noted that genetic and functional complement tests may support understanding of the mechanism, but should not be the only driver of decisions. [1]

For patients and caregivers, this set of papers mainly serves as background on why aHUS may first appear around a major life event (pregnancy or postpartum), a serious medical stress (severe high blood pressure, infection), or after an organ transplant, and why it can be difficult to tell apart from other causes of sudden anemia, low platelets, and kidney injury. Most of the evidence here comes from individual case reports and a small case series, so it cannot show how often these triggers lead to aHUS or predict what will happen for any one person. What remains uncertain across the reports is how best to separate trigger-related TMA that will resolve with trigger management alone from complement-driven disease that may persist or recur, especially when genetic results are unclear or when infections are present at the same time. [1] [2] [3] [4] [5] [6]

Across these small, exploratory reports (case reports and a 5-infant case series), eculizumab was repeatedly used when atypical hemolytic uremic syndrome (aHUS) or similar complement-driven clotting injury was suspected. The overall pattern was faster improvement in blood counts and some organ symptoms, while kidney outcomes varied from remission to ongoing kidney failure. These papers also highlight that aHUS can overlap with other conditions (such as lupus) and may involve organs beyond the kidneys, which can make treatment response harder to predict. [7] [8] [9] [10]

In infants with kidney-limited thrombotic microangiopathy (a clotting-injury pattern in small blood vessels), eculizumab led to complete remission in two and partial remission in two, while a fifth infant who did not receive eculizumab progressed to kidney failure by 11 months. The authors also reported signs of alternative complement pathway activation and several complement-related gene variants, which fits with a complement-driven process but was not fully functionally confirmed. One infant had a severe respiratory infection after eculizumab, followed by worsening blood and urine findings. [8]

In one adult with systemic lupus erythematosus (SLE) and thrombotic microangiopathy with aHUS-like features, eculizumab was followed by a rapid blood response within 6 days, including higher hemoglobin and platelets, along with symptom improvement and stable kidney function. Testing showed high levels of a blood marker of complement activation (soluble C5b-9) and a normal ADAMTS13 activity level, supporting a complement-related mechanism in that episode. [9]

Another SLE case showed that response can be limited when kidney injury is severe. Despite steroids, plasma exchange, dialysis, and then eculizumab, the patient remained dialysis-dependent, and a kidney biopsy showed thrombotic microangiopathy with collapsing glomerulopathy. The report emphasized how difficult it can be to separate aHUS from lupus-related clotting injury in the kidneys, and it noted the need to manage infection risk with complement blocking therapy. [10]

A separate case highlighted that aHUS can include serious brain complications. A woman with a CFH gene mutation had aHUS complicated by posterior reversible encephalopathy syndrome (PRES), and early eculizumab plus intensive supportive care was followed by complete neurologic recovery and discharge without lasting deficits; later episodes of PRES occurred but stabilized with ongoing treatment and blood pressure control. This is one patient, so it cannot show what will happen for most people, but it illustrates the range of organs that can be affected and the intensive monitoring sometimes needed. [7]

For patients and caregivers, these reports mainly add real-world detail about what has been seen after starting a complement blocker in different aHUS-like situations, including infants with kidney-limited disease, adults with lupus-related clotting injury, and a case with brain involvement (PRES). The consistent message is that blood-related problems may improve quickly in some people, while kidney recovery can be incomplete, especially when biopsy shows severe damage. Because the evidence here comes from single patients and a very small series, it cannot predict an individual persons outcome, and it remains uncertain which specific test patterns or genetic results best forecast who will recover kidney function.

These papers, all single-patient case reports, show that atypical hemolytic uremic syndrome (aHUS) can sometimes involve organs beyond the kidneys. Reported complications included severe lung bleeding, unusual bone marrow failure, blistering skin wounds with calcification, and repeated heart failure episodes occurring soon after a complement-blocking medicine infusion. Because each report describes only one person, it is not clear how often these problems happen or which patients are most at risk. [11] [12] [13] [14]

In a 72-year-old man with chronic kidney disease, aHUS was linked to diffuse alveolar hemorrhage (bleeding into the lungs) causing respiratory failure, confirmed by bronchoscopy. After plasma exchange and corticosteroids, both the blood cell damage pattern and the lung bleeding improved, and he was able to come off the ventilator; the report also notes that eculizumab was not used due to cost. [11]

In a 5-year-old boy, aHUS occurred together with a very low-cell bone marrow (10-15% cellularity) consistent with aplastic anemia, which is not typical for aHUS. Despite plasma exchange and later treatments including eculizumab, he did not improve and died from a massive pulmonary hemorrhage, highlighting that severe bleeding complications can occur in rare situations. [12]

In an 8-month-old infant, spontaneous blistering skin rupture with dystrophic wound calcification developed after about one month of treatment, and the report emphasized nurse-led, multidisciplinary supportive care including kidney and fluid monitoring, wound care, nutrition, pain control, and family support. The wounds gradually healed, kidney function recovered, and no aHUS recurrence was reported during a 3-month follow-up after discharge. [13]

In a 45-year-old woman with suspected complement-mediated thrombotic microangiopathy, acute heart failure worsening occurred within hours after each eculizumab infusion, improved when the drug was stopped, and returned after a reduced-dose rechallenge. The authors described this as a possible but unproven drug-related effect that needs more study, especially because many other factors in critical illness can affect the heart. [14]

For patients and caregivers, this set of reports mainly serves as background information showing that aHUS can sometimes have serious effects outside the kidneys, including lung bleeding, skin wounds, bone marrow problems, and heart strain. The reports do not establish how common these complications are, whether they share a single cause, or how reliably they respond to particular treatments, because each paper describes one person and circumstances varied widely. One report also raises a safety question about heart failure episodes occurring soon after eculizumab infusions, but a single case cannot prove cause and effect, so the overall risk remains uncertain.

Across this study, C5 inhibitor use during septic shock was mainly linked to higher rates of several serious complications rather than a clear change in short-term survival. The pattern included more problems with blood counts, kidneys, blood clotting, and major heart-related events, while 30-day death rates were similar between groups. Because the work used electronic health record data, it can show signals but cannot fully prove cause and effect. [15]

In a large, real-world comparison of eculizumab and ravulizumab in adults with septic shock (638 people in each group), those receiving C5 inhibition had higher rates of low platelets, acute kidney injury, blood clots, needing kidney replacement treatment, and major adverse heart-related events. There was no difference in 30-day mortality between groups. [15]

For people with atypical hemolytic uremic syndrome, this research is most relevant as background information about what was seen when very ill adults had septic shock while also having conditions that can be treated with C5 inhibitors. It highlights that, in this setting, complications involving platelets, kidneys, clotting, and the heart were reported more often, while short-term survival looked similar. It is still uncertain how much these results apply to people who are not in septic shock, because the study focused on a specific, high-risk hospital situation and used observational health record data. [15]

Across this paper, the main message is that drug choice can change short-term spending for atypical hemolytic uremic syndrome (aHUS), and the lowest-cost option depends on the time period considered. The analysis suggests larger differences early in treatment and continued higher costs for originator eculizumab across scenarios. It remains uncertain how these modeled costs compare to real-world spending because rebates, dosing patterns, and longer-term costs were not included. [16]

In a one-year cost-minimization model from the German statutory health insurance perspective, the eculizumab biosimilar Epysqli had lower modeled drug costs than originator eculizumab during the early phase (up to 13 weeks). At 13 weeks, cumulative costs were 124,941 euros for the biosimilar versus 172,466 euros for the originator. [16]

When compared with ravulizumab, the biosimilar was also modeled as slightly lower cost at 13 weeks (124,941 euros vs 127,062 euros). Sensitivity analyses suggested ravulizumab could become the lowest-cost option around 26 weeks in some scenarios, while originator eculizumab remained the most expensive at all time points examined. [16]

The authors noted key reasons the results may not match individual patients or longer-term budgeting: the model assumed the drugs have equal effectiveness and safety, used a one-year horizon, did not include pediatric dosing, and could not capture confidential rebates or real-world dosing and utilization. This means the results are best understood as a structured estimate of how published prices and dosing schedules can drive short-term cost differences. [16]

For patients and caregivers, this study mainly provides background on why insurance systems and hospitals may view similar aHUS medicines differently when considering budgets over months rather than years. It does not show differences in health outcomes, and it cannot predict what any one person will be charged or offered, especially where discounts, weight-based dosing, local contracts, or longer treatment durations apply. What remains uncertain is how these modeled cost patterns play out in real-world access decisions in Germany and in other countries with different pricing and reimbursement rules. [16]