# Thrombotic Microangiopathy > Thrombotic microangiopathy for NEET-SS Nephrology: TTP and ADAMTS13, Shiga toxin HUS, atypical HUS with eculizumab, anti-factor H and drug causes. - Canonical URL: https://prepelephant.com/topics/neet-ss/nephrology/thrombotic-microangiopathy-dm - Exam / course: NEET-SS · Subject: Nephrology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Thrombotic Microangiopathy", PrepElephant, https://prepelephant.com/topics/neet-ss/nephrology/thrombotic-microangiopathy-dm ## Direct answer Schistocytes on the film, a falling platelet count and a rising creatinine define the thrombotic microangiopathies, a family that splits three ways at the bedside: thrombotic thrombocytopenic purpura, where ADAMTS13 activity below 10 per cent lets ultra-large von Willebrand multimers shear platelets and plasma exchange is a minutes-count emergency; Shiga toxin haemolytic uraemic syndrome, where children follow bloody diarrhoea into a self-supporting illness that antibiotics may worsen; and atypical HUS, a complement dysregulation disease that owns the severe kidney injury and answers to eculizumab. Two discriminators do most of the diagnostic work — the ADAMTS13 assay, and whether the kidney or the brain bears the brunt. ## What you must remember - **TTP:** ADAMTS13 severe deficiency below 10 IU/dL — autoimmune in adults, congenital in Upshaw–Schulman syndrome; neurological signs dominate, kidney injury is characteristically mild, and untreated mortality approaches 90 per cent while exchange plus steroids rescue more than 80 per cent. - **Exchange details:** daily plasma exchange started on suspicion, not after confirmation; plasma infusion is acceptable while arranging it; caplacizumab, the anti-von Willebrand nanobody, blocks the platelet adhesion directly. - **STEC-HUS:** Escherichia coli O157:H7 and Shiga toxin; children with bloody diarrhoea; antibiotics and antimotility agents may worsen outcomes; care is supportive — exchange and eculizumab are not indicated. - **aHUS:** complement factor H, factor I, MCP, C3 mutations or anti-factor H antibodies; C3 often low; ADAMTS13 normal; eculizumab — the anti-C5 monoclonal — is the therapy, with meningococcal vaccination before or alongside. - **Indian paediatric nuance:** anti-factor H antibody-mediated HUS is reported commonly in Indian children, adding plasmapheresis and rituximab to eculizumab and making antibody testing part of the domestic work-up. - **Secondary TMA:** pregnancy and postpartum states, calcineurin inhibitors, VEGF inhibitors such as bevacizumab, gemcitabine, malignant hypertension, antiphospholipid syndrome and HIV — removing the trigger is the treatment. - **Biopsy signature:** arteriolar fibrin thrombi, mucoid intimal hyperplasia and double-contour basement membranes with scant immune deposits. - **Platelet rule:** do not transfuse platelets in TTP unless life-threatening bleeding — you are feeding the fire. ## Separating the three phenotypes at three in the morning A 28-year-old postpartum woman arrives confused, platelets 19, haemoglobin 7.4 with schistocytes, creatinine 2.1. Step one: she has TMA — now the phenotype. Send ADAMTS13 activity, a stool Shiga toxin PCR and complement C3, and take the drug list (calcineurin inhibitor? bevacizumab?) and the blood pressure. Step two: apply the prior probabilities — postpartum with predominant neurology and mild renal injury fits TTP; the same woman with creatinine 6 and quiet mentation fits pregnancy-associated aHUS; severe hypertension shifts the whole question toward malignant-phase TMA, where lowering blood pressure treats the mechanism. Step three: treat the worst plausible answer while assays pend — plasma exchange with steroids, because untreated TTP kills within days and exchange is safe if the answer turns out to be aHUS, simply insufficient. Step four: when ADAMTS13 returns above 10 per cent and C3 is low, pivot to eculizumab for aHUS, vaccinating against meningococcus and planning long-term complement blockade. Step five: if a child had walked in instead — a six-year-old, a week of bloody diarrhoea, creatinine 4 — the pathway would have been the opposite: supportive care, fluid and electrolyte discipline, dialysis as needed, and no exchange, no eculizumab, no antibiotics. ## Where the examiner hunts The favourite trap is the creatinine: "TTP with a creatinine of 7" should make you distrust the label, because severe kidney injury belongs to HUS, malignant hypertension and drug TMA — the exam wants you to re-examine the diagnosis, not double the exchange. The second is the sequencing question: plasma first or assay first? Plasma therapy starts on suspicion; the assay follows and neither waits for the other. The third is the Indian framing — the child with HUS in Indian practice deserves anti-factor H antibody testing, since antibody-positive disease is treated with plasmapheresis and rituximab alongside eculizumab, a combination Western textbooks underemphasise. And the vaccination question, meningococcal cover before eculizumab, remains the single most reliable one-mark item in this territory. ## Frequently asked questions ### What ADAMTS13 level defines TTP? Activity below 10 IU/dL — severe deficiency; levels above 10 per cent point instead toward HUS, atypical HUS or secondary TMA. ### Why must plasma exchange never be delayed? Untreated TTP carries mortality near 90 per cent; exchange plus corticosteroids — and now caplacizumab — reduce it dramatically, and the assay takes days. ### How is Shiga toxin HUS managed? Supportively — fluids, electrolytes, dialysis and transfusion as needed; antibiotics and antimotility agents may aggravate disease. ### What must precede eculizumab? Meningococcal vaccination (with antibiotics bridging if therapy cannot wait), because C5 blockade removes terminal complement defence. ### What is anti-factor H antibody HUS? An atypical HUS subtype driven by autoantibodies, reported frequently in Indian children, treated with plasmapheresis and rituximab in addition to complement blockade. ### Which drugs and states cause secondary TMA? Calcineurin inhibitors, VEGF-pathway inhibitors, gemcitabine, malignant hypertension, pregnancy and postpartum states, antiphospholipid syndrome and HIV.