Post-partum acute kidney injury: sorting placental and non-placental thrombotic microangiopathies using the trajectory of biomarkers

A case-based narrative review of pregnancy-associated atypical hemolytic uremic syndrome/complement-mediated thrombotic microangiopathy

Atypical hemolytic uremic syndrome is a complement-mediated thrombotic microangiopathy caused by uncontrolled activation of the alternative complement pathway in the setting of autoantibodies to or rare pathogenic genetic variants in complement proteins. Pregnancy may serve as a trigger and unmask atypical hemolytic uremic syndrome/complement-mediated thrombotic microangiopathy (aHUS/CM-TMA), which has severe, life-threatening consequences. It can be difficult to diagnose aHUS/CM-TMA in pregnancy due to overlapping clinical features with other thrombotic microangiopathy syndromes including hypertensive disorders of pregnancy. However, the distinction among thrombotic microangiopathy etiologies in pregnancy is important because each syndrome has specific disease management and treatment. In this narrative review, we discuss 2 cases to illustrate the diagnostic challenges and evolving approach in the management of pregnancy-associated aHUS/CM-TMA. The first case involves a 30-year-old woman presenting in the first trimester who was diagnosed with aHUS/CM-TMA and treated with eculizumab from 19 weeks' gestation. Genetic testing revealed a likely pathogenic variant in CFI. She successfully delivered a healthy infant at 30 weeks' gestation. In the second case, a 22-year-old woman developed severe postpartum HELLP syndrome, requiring hemodialysis. Her condition improved with supportive management, yet investigations assessing for aHUS/CM-TMA remained abnormal 6 months postpartum consistent with persistent complement activation but negative genetic testing. Through detailed case discussion describing tests assessing for placental health, fetal anatomy, complement activation, autoantibodies to complement regulatory proteins, and genetic testing for aHUS/CM-TMA, we describe how these results aided in the clinical diagnosis of pregnancy-associated aHUS/CM-TMA and assisted in guiding patient management, including the use of anticomplement therapy.

Pregnancy as a susceptible state for thrombotic microangiopathies

Pregnancy and the postpartum period represent phases of heightened vulnerability to thrombotic microangiopathies (TMAs), as evidenced by distinct patterns of pregnancy-specific TMAs (e.g., preeclampsia, HELLP syndrome), as well as a higher incidence of nonspecific TMAs, such as thrombotic thrombocytopenic purpura or hemolytic uremic syndrome, during pregnancy. Significant strides have been taken in understanding the underlying mechanisms of these disorders in the past 40 years. This progress has involved the identification of pivotal factors contributing to TMAs, such as the complement system, ADAMTS13, and the soluble VEGF receptor Flt1. Regardless of the specific causal factor (which is not generally unique in relation to the usual multifactorial origin of TMAs), the endothelial cell stands as a central player in the pathophysiology of TMAs. Pregnancy has a major impact on the physiology of the endothelium. Besides to the development of placenta and its vascular consequences, pregnancy modifies the characteristics of the women's microvascular endothelium and tends to render it more prone to thrombosis. This review aims to delineate the distinct features of pregnancy-related TMAs and explore the contributing mechanisms that lead to this increased susceptibility, particularly influenced by the "gravid endothelium." Furthermore, we will discuss the potential contribution of histopathological studies in facilitating the etiological diagnosis of pregnancy-related TMAs.

Atypical Hemolytic-Uremic Syndrome: Genetic Basis, Clinical Manifestations, and a Multidisciplinary Approach to Management

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy (TMA) defined by the triad of hemolytic anemia, thrombocytopenia, and acute kidney injury. Microthrombi develop in the glomerular capillaries secondary to endothelial damage and exert shear stress on red blood cells, consume platelets, and contribute to renal dysfunction and failure. Per current understanding of pathophysiology, HUS is classified into infectious, secondary, and atypical disease. The most common etiology is infectious sequelae of Shiga toxin-producing Escherichia coli (STEC); other causative organisms include shigella and salmonella. Secondary HUS arises from cancer, chemotherapy, solid organ and hematopoietic stem cell transplant, pregnancy, or autoimmune disorders. Primary atypical hemolytic-uremic syndrome (aHUS) is associated with genetic mutations in complement and complement regulatory proteins. Under physiologic conditions, complement regulators keep the alternative complement system continuously active at low levels. In times of inflammation, mutations in complement-related proteins lead to uncontrolled complement activity. The hyperactive inflammatory state leads to glomerular endothelial damage, activation of the coagulation cascade, and TMA findings. Atypical hemolytic-uremic syndrome is a rare disorder with a prevalence of 2.21 to 9.4 per million people aged 20 years or younger; children between the ages of 0 and 4 are most affected. Multidisciplinary health care is necessary for timely management of its extra-renal manifestations. These include vascular disease of the heart, brain, and skin, pulmonary hypertension and hemorrhage, and pregnancy complications. Adequate screening is required to monitor for sequelae. First-line treatment is the monoclonal antibody eculizumab, but several organ systems may require specialized interventions and coordination of care with sub-specialists.

Pregnancy in Complement-Mediated Thrombotic Microangiopathy: Maternal and Neonatal Outcomes

Rationale & Objective

Pregnancy, delivery, and neonatal outcomes in women with complement-mediated thrombotic microangiopathy (cTMA) have not been well described. A better understanding of these outcomes is necessary to provide women with competent pregnancy counseling.

Study Design

Cohort study.

Setting and Participants

Women with a history of cTMA and pregnancies enrolled into the Vienna thrombotic microangiopathy cohort.

Exposure

New onset or relapses of cTMA.

Outcomes

Pregnancy, delivery, and neonatal outcomes of pregnancies in women (a) before cTMA manifestation, (b) complicated by pregnancy-associated cTMA (P-cTMA), and (c) after first manifestation of cTMA or P-cTMA.

Analytical Approach

Mixed models were used to adjust the comparison of pregnancy, delivery, and neonatal outcomes between conditions (before, with, and after cTMA) for repeated pregnancies using the mother's ID as random factor. In addition, the fixed factors, mother's age and neonate's sex, were used for adjustment. For (sex-adjusted and age-adjusted) centile outcomes, only the mother's age was used. Adjusted odds ratios were derived from a generalized linear mixed model with live birth as the outcome. Least squares means and pairwise differences between them were derived from the linear mixed models for the remaining outcomes.

Results

28 women reported 74 pregnancies. Despite higher rates of fetal loss before the diagnosis of P-cTMA and preterm births with P-cTMA, most of the women were able to conceive successfully. Neonatal development in all 3 conditions of pregnancies was excellent. Pregnancy and neonatal outcomes were better in women with a pregnancy after the diagnosis of cTMA.

Limitations

Although our data set comprises a considerable number of 74 pregnancies, the effective sample size is lower because only 28 mothers with multiple pregnancies were observed. The statistical power for detecting clinically relevant effects was probably low. A recall bias for miscarriages cannot be ruled out.

Conclusions

Prepregnancy counseling of women with a history of cTMA can be supportive of their desire to become pregnant.

Maternal-Perinatal Variables in Patients with Severe Preeclampsia Who Develop Acute Kidney Injury

Introduction: At present, we are witnessing an increase in preeclampsia, especially the most severe forms, which are associated with an increased risk of maternal-perinatal morbidity and mortality. As a severity criterion, acute kidney injury (AKI) has been associated with a worse prognosis, and for this reason, the maternal and perinatal variables associated with AKI in patients with severe preeclampsia (SP) were analysed in this study. Methods: An observational, retrospective, single-centre study of patients with SP treated at a tertiary hospital between January 2007 and December 2018 was conducted. The case criteria based on the criteria established by the ACOG Practice Guidelines for Gestational Hypertension and Preeclampsia. AKI is considered when serum creatinine exceeds 1.1 mg/dL in a pregnant woman with previously normal renal function. In patients with existing chronic kidney disease (CKD), it is referred to as AKI if the baseline serum creatinine increases by 1.5 fold. Pregestational, gestational and postpartum variables were analysed up to 12 weeks postpartum using univariate and multivariate logistic regression analysis. Results: During the study period, 76,828 births were attended, and 303 pregnant women were diagnosed with SP. The annual incidence of SP increased gradually throughout the study period, reaching 1.79/100 births/year in 2018. Acute kidney injury (AKI) occurred in 24.8% of the patients. The multivariate analysis revealed an increased association with a history of previous CKD, the use of assisted reproductive techniques and caesarean section. Uric acid and thrombotic microangiopathy (TMA) had a high correlation with AKI. Indications for caesarean section are associated with AKI in SP. Regarding perinatal outcomes in cases of AKI, there was a higher percentage of neonates who required foetal lung maturation with steroids and an increased need for NICU admission. No case of maternal death was recorded; however, an increase in neonatal mortality was found among patients who did not develop AKI. After 12 weeks postpartum, 72 patients were referred to the nephrology consultation for persistent hypertension, proteinuria or renal failure. Conclusions: In preeclampsia, AKI is a common complication, especially among patients with a history of CKD, those who became pregnant using assisted reproduction techniques and those who delivered via caesarean section. The perinatal impact of AKI is mainly centred on a higher rate of NICU admission and a lower mortality rate. Among biochemical and haematological markers, the uric acid level prior to renal failure has a direct and significant correlation with the risk of AKI, as does the development of TMA in patients with preeclampsia. Therefore, the monitoring of renal function in cases of preeclampsia should be strict, and referral for a nephrology consultation may be necessary in some cases.

Complement activation and blockade in massive post-partum haemorrhage, thrombotic microangiopathy and acute kidney injury: a case report

Background

Thrombotic microangiopathy (TMA)-mediated acute kidney injury (AKI) following massive haemorrhage is a rare but severe complication of the post-partum period. It is associated with a poor renal prognosis and a high risk of end-stage kidney disease. Complement activation may occur in this picture. However, whether complement activation, and thus complement blockade, may be critically relevant in this setting is unknown.

Case presentation

A 50 year-old woman presented with massive delayed post-partum haemorrhage (PPH). Despite bleeding control and normalization of coagulation parameters, she rapidly developed AKI stage 3 associated with dysmorphic microhematuria and proteinuria up to 2 g/day with the need of renal replacement therapy. Blood tests showed signs of TMA associated with markedly increased sC5b-9 and factor Bb plasma levels, respectively markers of terminal and alternative complement pathway over-activation. This clinical picture prompted us to initiate anti-C5 therapy. sC5b-9 normalized within 12 h after the first dose of eculizumab, factor Bb and C3 after seven days, platelet count after nine days and haptoglobin after 3 weeks. The clinical picture improved rapidly with blood pressure control within 48 h. Diuresis resumed after three days, kidney function rapidly improved and haemodialysis could be discontinued after the sixth and last dose. Serum creatinine returned to normal two years after presentation.

Conclusions

We suggest that massive PPH induced major activation of complement pathways, which ultimately lead to TMA-induced AKI. Various causes, such as oocyte-donation, the potential retention of placental material and the use of tranexamic acid may have contributed to complement activation due to PPH. The prompt administration of anti-C5 therapy may have rapidly restored kidney microcirculation patency, thus reversing signs of TMA and AKI. We propose that complement activation may represent a major pathophysiological player of this complication and may provide a novel therapeutic avenue to improve renal prognosis in TMA-induced AKI following massive PPH.

Association of lactate dehydrogenase with mortality in incident hemodialysis patients

BACKGROUND

Lactate dehydrogenase (LDH) plays a role in the glucose metabolism of the human body. Higher LDH levels have been linked to mortality in various cancer types; however, the relationship between LDH and survival in incident hemodialysis (HD) patients has not yet been examined. We hypothesized that higher LDH level is associated with higher death risk in these patients.

METHODS

We examined the association of baseline and time-varying serum LDH with all-cause, cardiovascular and infection-related mortality among 109 632 adult incident HD patients receiving care from a large dialysis organization in the USA during January 2007 to December 2011. Baseline and time-varying survival models were adjusted for demographic variables and available clinical and laboratory surrogates of malnutrition-inflammation complex syndrome.

RESULTS

There was a linear association between baseline serum LDH levels and all-cause, cardiovascular and infection-related mortality in both baseline and time-varying models, except for time-varying infection-related mortality. Adjustment for markers of inflammation and malnutrition attenuated the association in all models. In fully adjusted models, baseline LDH levels ≥360 U/L were associated with the highest risk of all-cause mortality (hazard ratios = 1.19, 95% confidence interval 1.14-1.25). In time-varying models, LDH >280 U/L was associated with higher death risk in all three hierarchical models for all-cause and cardiovascular mortality.

CONCLUSIONS

Higher LDH level >280 U/L was incrementally associated with higher all-cause and cardiovascular mortality in incident dialysis patients, whereas LDH <240 U/L was associated with better survival. These findings suggest that the assessment of metabolic functions and monitoring for comorbidities may confer survival benefit to dialysis patients.

Preeclampsia, HELLP Syndrome, and Postpartum Renal Failure with Thin Basement Membrane Nephropathy: Case Report and a Brief Review of Postpartum Renal Failure

A 36-year-old primigravida female from a birthing center was referred for elevated blood pressure to the hospital two days after normal spontaneous vaginal delivery with nausea, vomiting, and diarrhea. During this two-day period, she was experiencing persistent vaginal bleeding and lower abdominal pains for which she took six doses of 600 mg ibuprofen. Further laboratory evaluation reflected leukocytosis, anemia, thrombocytopenia, elevation of liver enzymes, and renal failure with hyperkalemia requiring emergent hemodialysis once in the Medical Intensive Care Unit (MICU). She was diagnosed with HELLP syndrome with underlying preeclampsia. A week later, due to hypertension controlled with medications and nonoliguric renal failure with no active urine sediments, a renal biopsy was indicated to direct management. The renal biopsy supported the diagnosis of diffuse severe acute tubulointerstitial nephritis with hypereosinophilia and thin basement membrane nephropathy (see figures). She was subsequently treated with high-dose steroids which resulted in the normalization of blood pressures and renal function returning to baseline. We report the first case of acute tubulointerstitial nephritis in an individual with thin basement membrane nephropathy secondary to postpartum complications.

Acute kidney injury during pregnancy leads to increased sFlt-1 and sEng and decreased renal T regulatory cells in pregnant rats with HELLP syndrome

BACKGROUND

The incidence of acute kidney injury (AKI) during pregnancy precedes a high maternal mortality rate of 20-40%. AKI during pregnancy has multiple etiologies; however, the more common are maternal hypertensive disorders, which include preeclampsia and HELLP (hemolysis, elevated liver enzyme, low platelet) syndrome. Therefore, we sought to assess the impact of AKI on blood pressure, kidney injury, and anti-angiogenic factors during pregnancies with and without HELLP syndrome.

METHODS

On gestational day (GD) 12, mini-osmotic pumps were inserted into a subset of normal pregnant (NP) rats infusing 4.7 μg/kg soluble fms-like tyrosine kinase-1 (sFlt-1) and 7 μg/kg soluble endoglin (sEng) to induce HELLP syndrome. On GD18, the renal pedicles were occluded for 45 min to induce AKI via bilateral ischemia reperfusion in a subset of NP (n = 18) or HELLP (n = 20) rats. Control NP (n = 20) and HELLP (n = 20) rats underwent a SHAM surgery on GD18. Plasma, urine, and maternal organs were saved for further analysis. Renal injury was assessed via renal histopathology, glomerular filtration rate (GFR), T cell infiltration, and assessment of kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL). Data was measured via two-way analysis of variance with Tukey's test for post hoc analysis.

RESULTS

Blood pressures were increased in HELLP+AKI rats (p = 0.0001); both NP+AKI and HELLP+AKI rats had increased lactate dehydrogenase (p < 0.0001) and aspartate aminotransferase levels (p < 0.0001), and decreased platelet levels (p < 0.001) vs. NP rats. HELLP+AKI (p = 0.002) and HELLP rats (p = 0.0002) had evidence of renal fibrosis vs. NP rats. GFR was decreased in HELLP+AKI (p = 0.01) rats vs. NP rats. Urinary KIM-1 was increased in NP+AKI rats vs. NP (p = 0.003) and HELLP rats (p = 0.01). HELLP+AKI rats had increased urinary KIM-1 vs. NP (p = 0.0008) and HELLP rats (p = 0.004) and increased NGAL vs. HELLP rats (p = 0.002). HELLP+AKI rats had increased sFlt-1 (p = 0.009) vs. NP rats. NP+AKI (p = 0.02) and HELLP+AKI (p = 0.007) rats had increased sEng vs. NP rats. CD3+CD4+ T cells were significantly increased in HELLP+AKI rats vs. NP (p = 0.0002) and NP+AKI (p = 0.05) rats. T regulatory cells were significantly decreased in HELLP+AKI (p = 0.03) and NP+AKI (p = 0.02) rats vs. NP rats; there were no changes between groups in T helper 17 cells (p = 0.34).

CONCLUSION

The findings in this study suggest that AKI during pregnancy contributes to increased blood pressure and biochemical markers for HELLP syndrome, creates an anti-angiogenic imbalance, and exacerbates kidney injury as shown on histopathology, GFR, and kidney injury markers.

Pregnancies in kidney transplant recipients with complement gene variant-mediated thrombotic microangiopathy

Background

Pregnancies in patients with complement gene variant-mediated thrombotic microangiopathy (cTMA) are challenging, and pregnancies in such patients after kidney transplantation (KTX) are even more so.

Methods

We identified nine pregnancies following KTX of three genetically high-risk cTMA patients enrolled in the Vienna thrombotic microangiopathy cohort. Preventive plasma therapy was used in three pregnancies, and one patient had ongoing eculizumab (ECU) therapy during two pregnancies.

Results

Seven out of nine pregnancies (78%) resulted in the delivery of healthy children. The other two included one early abortion at gestational Week 12 during ongoing ECU therapy and one late foetal death at gestational Week 33 + 3, most likely not related to complement dysregulation. Kidney transplant function after delivery remained stable in all but one pregnancy. In the aforementioned case, a severe cTMA flare occurred after delivery despite use of preventive plasma infusions. Kidney graft function could be rescued in this patient by ECU. As such, successful pregnancies can be accomplished in kidney transplant recipients (KTRs) with a history of cTMA. We used preemptive plasma therapy or ongoing ECU treatment in selected cases.

Conclusions

Thus, becoming pregnant can be encouraged in KTRs with native kidney cTMA. Extensive preconception counselling, however, is mandatory in such cases.

Acute Kidney Injury in Pregnancies Complicated With Preeclampsia or HELLP Syndrome

Acute kidney injury that occurs during pregnancy or in the post-partum period (PR-AKI) is a serious obstetric complication with risk of significant associated maternal and fetal morbidity and mortality. Recent data indicates that the incidence of PR-AKI is increasing, although accurate calculation is limited by the lack of a uniform diagnostic criteria that is validated in pregnancy. Hypertensive and thrombotic microangiopathic disorders of pregnancy have been identified as major contributors to the burden of PR-AKI. As is now accepted regarding preeclampsia, HELLP syndrome and atypical hemolytic uremic syndrome, it is believed that PR-AKI may have long-term renal, cardiovascular and neurocognitive consequences that persist beyond the post-partum period. Further research regarding PR-AKI could be advanced by the development of a pregnancy-specific validated definition and classification system; and the establishment of refined animal models that would allow researchers to further elucidate the mechanisms and sequelae of the disorder.