ICU · Diagnostics
ICU biomarkers: procalcitonin, lactate, troponin, BNP, and CRP
Also known as ICU biomarkers · Procalcitonin · Lactate · Troponin · BNP · NT-proBNP · CRP · D-dimer · suPAR · Copeptin · MINS · hs-cTn
Biomarkers in ICU: objective measures that guide diagnosis, prognosis, and treatment. KEY biomarkers: (1) PROCALCITONIN (PCT): bacterial infection marker — rises in bacterial sepsis, stays low in viral/non-infective. Guides antibiotic duration (PRORATA, Bouadma 2010 — antibiotic stewardship). (2) LACTATE: tissue hypoperfusion marker — elevated in shock, sepsis, mesenteric ischaemia. Guide resuscitation (lactate clearance 10%/h; Jansen 2010, ANDROMEDA-SHOCK 2019). (3) TROPONIN (hs-cTn): myocardial injury — type 1 MI (atherosclerotic plaque rupture), type 2 MI (supply-demand mismatch — common in ICU), and MINS (myocardial injury after non-cardiac surgery — AHA 2021). (4) BNP/NT-proBNP: heart failure — elevated in volume overload, cardiac dysfunction. (5) CRP: inflammation — nonspecific, trends useful. (6) D-DIMER: fibrin turnover — elevated in VTE, DIC, arterial thrombosis, inflammation, malignancy, pregnancy (non-specific, high negative predictive value). (7) suPAR (soluble urokinase-type plasminogen activator receptor): inflammation/prognosis — predicts mortality in sepsis and critical illness. (8) COPEPTIN (CT-proAVP): vasopressin surrogate — quantifies stress response and arginine-vasopressin axis, prognostic in shock. Each has strengths, limitations, and specific clinical applications — always interpret in clinical context, not in isolation.
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Red flags
- Rising lactate despite resuscitation → ongoing hypoperfusion, mesenteric ischaemia, or mitochondrial dysfunction
- Procalcitonin >2 → bacterial sepsis likely, start antibiotics
- Procalcitonin not falling with antibiotics → wrong drug, inadequate source control, resistant organism
- Troponin elevated in ICU — often type 2 MI (supply-demand), not necessarily type 1 (atherosclerotic); do NOT automatically PCI
- BNP/NT-proBNP high → heart failure, but also elevated in renal failure, PE, sepsis
- D-dimer normal → VTE/DIC unlikely (high NPV); elevated is non-specific
- suPAR high in septic shock → higher mortality — escalate
- Copeptin very high in shock → marked vasopressin axis activation, consider vasopressin therapy
- Lactate >4 mmol/L + vasopressor requirement = septic shock (Sepsis-3)
- Rising troponin post-op without ischaemic features = MINS — prognostic, not automatically ACS
Meet the patient
A 64-year-old man arrives in septic shock from a urinary source: he needs noradrenaline to hold a mean arterial pressure of 65 mm Hg or greater and his lactate stays over 2 mmol/L despite volume — the Sepsis-3 picture of septic shock, with hospital mortality above 40 per cent.[19] His procalcitonin is high on admission and, by day two, his lactate has cleared and the PCT is falling, yet the troponin is still creeping upward.[1][17]
The registrar asks the question every examiner is really asking: four numbers are abnormal — which one changes what you do in the next hour, and which one changes what you do this afternoon? This whole topic is the answer to that question. Lactate drives the next hour; procalcitonin drives the antibiotic course; troponin drives the cardiology conversation; NT-proBNP drives the diuresis.[1][4][6]
References22ShowHide
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- [2]Jansen TC, van Bommel J, Schoonderbeek FJ, et al. Early lactate-guided therapy in intensive care unit patients: a multicenter, open-label, randomized controlled trial Am J Respir Crit Care Med, 2010.PMID 20463176
- [3]Lee KK, Doudesis D, Anwar M, et al. Development and validation of a decision support tool for the diagnosis of acute heart failure: systematic review, meta-analysis, and modelling study BMJ, 2022.PMID 35697365
- [4]Chapman AR, Adamson PD, Shah ASV, et al. High-Sensitivity Cardiac Troponin and the Universal Definition of Myocardial Infarction Circulation, 2020.PMID 31587565
- [5]Póvoa P. C-reactive protein: a valuable marker of sepsis Intensive Care Med, 2002.PMID 11904651
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- [12]Levi M, Toh CH, Thachil J, et al. Guidelines for the diagnosis and management of disseminated intravascular coagulation. British Committee for Standards in Haematology Br J Haematol, 2009.PMID 19222477
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- [14]Gussen H, Hohlstein P, Bartneck M, et al. Neutrophils are a main source of circulating suPAR predicting outcome in critical illness J Intensive Care, 2019.PMID 31061709
- [15]Lee JH, Chan YH, Lai OF, et al. Vasopressin and copeptin levels in children with sepsis and septic shock Intensive Care Med, 2013.PMID 23344831
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- [17]Hernández G, Ospina-Tascón GA, Damiani LP, et al. Effect of a Resuscitation Strategy Targeting Peripheral Perfusion Status vs Serum Lactate Levels on 28-Day Mortality Among Patients With Septic Shock: The ANDROMEDA-SHOCK Randomized Clinical Trial JAMA, 2019.PMID 30772908
- [18]van Es N, Kraaijpoel N, Klok FA, et al. The original and simplified Wells rules and age-adjusted D-dimer testing to rule out pulmonary embolism: an individual patient data meta-analysis J Thromb Haemost, 2017.PMID 28106338
- [19]Singer M, Deutschman CS, Seymour CW, et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) JAMA, 2016.PMID 26903338
- [20]Jones AE, Shapiro NI, Trzeciak S, et al. Lactate clearance vs central venous oxygen saturation as goals of early sepsis therapy: a randomized clinical trial JAMA, 2010.PMID 20179283
- [21]Righini M, Van Es J, Den Exter PL, et al. Age-adjusted D-dimer cutoff levels to rule out pulmonary embolism: the ADJUST-PE study JAMA, 2014.PMID 24643601
- [22]Huang DT, Yealy DM, Filbin MR, et al. Procalcitonin-Guided Use of Antibiotics for Lower Respiratory Tract Infection N Engl J Med, 2018.PMID 29781385