1,329 calculators and references across 60 specialties, with formula confidence shown up front.
Allowable Blood Loss Calculator Explanation and Clinical Context Allowable Blood Loss represents the maximum amount of blood a patient can safely lose before reaching a predefined critical hematocrit threshold during surgery or acute bleeding. The calculation is based on the estimated blood volume multiplied by the proportional change in hematocrit from the initial value to the acceptable minimum value. This approach
Altitude Cardiac Stress Index (ACSI): Explanation and Clinical Context The ACSI is a pragmatic, heuristic tool intended to summarize cardiac stress loads for athletes training or competing at altitude. It integrates key determinants of hypoxic cardiac strain: absolute altitude and ascent rate (as proxies for ambient hypoxia burden), acclimatization time, resting oxygen saturation, heart rate, blood pressure, and hema
Alveolar Gas Equation Explanation and Clinical Context The alveolar gas equation estimates alveolar oxygen partial pressure PAO2 using inspired oxygen fraction FiO2, barometric pressure Patm, water vapor pressure PH2O, arterial carbon dioxide PaCO2 and respiratory quotient RQ. The formula used here is PAO2 equals FiO2 times Patm minus PH2O minus PaCO2 divided by RQ. Normal PAO2 depends on FiO2 and altitude. At sea le
Ambler Risk Score: Explanation and Clinical Context The Ambler Risk Score is a validated risk model designed to predict operative mortality following cardiac surgery. It incorporates patient demographics, clinical characteristics, and procedural factors into a logistic regression model. Key variables include age, sex, previous cardiac surgery, urgency of procedure, baseline renal function (creatinine), left ventricul
Ambler Score: Explanation and Clinical Context Ambler Score is a validated risk prediction model for estimating 30-day mortality after cardiac surgery, including CABG, valve procedures, and combined operations. It uses multiple preoperative patient characteristics, cardiac function parameters, and operation-related factors to calculate a probability of death using logistic regression. This tool allows clinicians to i
Ambulatory Blood Pressure Variability (ABPV) Index: Explanation and Clinical Context The Ambulatory Blood Pressure Variability (ABPV) Index quantifies the fluctuations of blood pressure over 24 hours using data from ambulatory blood pressure monitoring (ABPM). It provides several metrics including mean BP, standard deviation (SD), coefficient of variation (CV), and average real variability (ARV) to comprehensively as
The audited source currently returns an empty page. This catalog entry is retained for coverage and monitoring, but no clinical content or calculation is asserted.
Amplatzer Device Sizing Index (ADSI): Explanation and Clinical Context The Amplatzer Device Sizing Index (ADSI) is a validated tool to guide the selection of the optimal Amplatzer Septal Occluder (ASO) for closing Atrial Septal Defects (ASD). It is calculated as the ratio of the selected device diameter to the balloon-stretched ASD diameter. An ADSI value between 1.2 and 1.5 is generally considered optimal, ensuring
Amyloidosis Cardiac Stage (Mayo 2012): Explanation and Clinical Context The Mayo 2012 staging system is designed for patients with systemic light-chain (AL) amyloidosis and provides prognostic information based on cardiac involvement. It uses three biomarkers: NT-proBNP (>1800 pg/mL), Troponin T (>0.025 ng/mL), and difference in free light chains (dFLC >180 mg/L). Each abnormal biomarker counts as one risk factor. St
Anaerobic Threshold (AT) Value Index: Explanation and Clinical Context The Anaerobic Threshold (AT) represents the exercise intensity at which lactate begins to accumulate in the blood, signaling a shift from predominantly aerobic to anaerobic metabolism. AT Index is calculated using VO2 max and heart rate at AT, providing a relative measure of cardiovascular and metabolic efficiency during exercise. Normal AT occurs
Anesthesia Recovery Score Explanation and Clinical Context The Anesthesia Recovery Score also known as the Aldrete Score is a widely used clinical tool to evaluate patient readiness for discharge from the post anesthesia care unit. It assesses five physiological domains including activity respiration circulation consciousness and oxygen saturation. Each category is scored from zero to two with a maximum total score o
: Explanation and Clinical Context This tool combines the ASA Physical Status (ASA-PS) classification with cardiac-specific “risk modifiers” and the presence of active cardiac conditions to structure perioperative decision-making for patients with cardiovascular disease who are undergoing noncardiac surgery. The ASA-PS conveys baseline physiological reserve and comorbidity burden, and the emergency modifier “E” indic
Ankle Brachial Index For PAD Risk. Clinical Explanation and Context The Ankle Brachial Index is a simple and validated noninvasive test used to detect the presence and severity of peripheral artery disease. It is calculated by dividing the systolic blood pressure at the ankle by the highest systolic blood pressure measured in both arms. ABI provides an objective assessment of lower extremity perfusion and correlates
Anticoagulation Regimen Safety Index (Warfarin vs LMWH): Explanation and Clinical Context This tool estimates bleeding risk when choosing between Warfarin and Low Molecular Weight Heparin (LMWH) for anticoagulation therapy. The score incorporates key clinical variables known to influence bleeding risk, including advanced age, impaired renal function, prior history of major bleeding, and concurrent antiplatelet therap
Aortic Aneurysm Expansion Index (AAEI): Explanation and Clinical Context The Aortic Aneurysm Expansion Index (AAEI) quantifies the annual relative increase in aortic diameter, expressed as a percentage per year. It is calculated using the formula: (Follow-up Diameter - Baseline Diameter) / (Baseline Diameter × Time Interval) × 100%. AAEI helps clinicians identify patients at risk of rapid aneurysm growth and potentia
Aortic Compliance Index (ACI): Explanation and Clinical Context The Aortic Compliance Index (ACI) represents the ability of the aorta to expand and contract with each cardiac cycle in response to changes in blood pressure. It reflects the elastic properties of the aortic wall and serves as a surrogate marker of arterial stiffness. The formula used is: ACI = Stroke Volume / Pulse Pressure where Stroke Volume (SV) is t
Aortic Distensibility Index (ADI): Explanation and Clinical Context The Aortic Distensibility Index (ADI) is a measure of aortic elasticity, calculated using the change in aortic diameter during the cardiac cycle relative to pulse pressure. It reflects the ability of the aorta to expand and recoil with each heartbeat. Higher ADI values indicate a more compliant aorta, while lower values suggest increased stiffness, w
Aortic Root Z-Score (Boston Formula): Explanation and Clinical Context The Aortic Root Z-score is a body size–adjusted measurement that quantifies how a patient’s aortic root dimension compares to population-based reference values. The Boston formula, derived from pediatric and young adult cohorts, provides a reliable way to normalize aortic root diameter according to body surface area (BSA). A Z-score represents the
Aortic Stiffness Index (ASI): Explanation and Clinical Context The Aortic Stiffness Index (β) is a non-invasive echocardiographic measure of the intrinsic stiffness of the ascending aorta. It reflects the mechanical properties of the aortic wall and is calculated using systolic and diastolic blood pressures and the corresponding aortic diameters. An increased ASI indicates reduced aortic compliance and is associated
Aortic Valve Area by Continuity Equation: Explanation and Clinical Context Aortic valve area is a fundamental parameter used to assess the severity of aortic stenosis. The continuity equation is the most widely endorsed method for calculating aortic valve area because it is grounded in the principle of conservation of mass. According to this principle, flow in the left ventricular outflow tract must equal flow across
APACHE II score explanation and clinical context APACHE II is a severity scoring system developed to estimate risk of hospital mortality for patients admitted to intensive care. The score is the sum of an acute physiology score derived from the worst value in the first 24 hours for twelve physiologic variables plus points for age plus points for chronic health status. A higher total score indicates greater physiologi
APACHE II Score: Explanation and Clinical Context The APACHE II (Acute Physiology And Chronic Health Evaluation II) score is a widely used ICU severity-of-disease classification system that sums abnormalities in 12 physiologic variables (the Acute Physiology Score, APS), adds age points, and adds chronic health points to provide an admission severity score (range 0–71). Higher scores correlate with higher hospital mo
APACHE IV calculation note APACHE IV is a validated severity scoring system published for hospital mortality assessment in critically ill adults. The original model uses many physiologic variables combined with spline terms and coefficients derived from a very large multicenter dataset. Reproducing the exact predicted mortality requires the original model coefficients or authorized software. This tool collects the da
APACHE-IV: Purpose, limitations, and clinical context APACHE-IV (Acute Physiology and Chronic Health Evaluation, version IV) is an updated severity-of-illness model developed from a very large multi-center ICU cohort to estimate hospital mortality and length of stay for critically ill adults. The original publication describes a multivariable logistic procedure using first-24-hour physiologic data, age, chronic healt
APACHE-Cardiac Subset: Explanation and Clinical Context The APACHE-Cardiac Subset is a risk stratification tool adapted from the APACHE III scoring system, specifically designed for cardiac intensive care patients. It incorporates variables including age, heart rate, mean arterial pressure, serum creatinine, PaO2/FiO2 ratio, and mechanical ventilation status to estimate mortality risk. The score allows clinicians to
APGAR Score Explanation and Clinical Context APGAR Score is a standardized clinical tool to rapidly assess the status of a newborn during the first moments of life. It evaluates Appearance Pulse Grimace Activity and Respiration each scored from zero to two resulting in a total score between zero and ten. Scores of seven to ten generally indicate good condition while four to six suggests moderate depression and may re
Apical HCM Index: Explanation and Clinical Context The Apical HCM Index is a simple echocardiographic metric calculated as the ratio of maximal apical wall thickness to the left ventricular end-diastolic diameter (LVEDD). It was first described by Kobayashi et al. to identify patients with apical hypertrophic cardiomyopathy (HCM), particularly in populations where this variant is more prevalent, such as in Japan. An
ApoB/ApoA1 Ratio: Explanation and Clinical Context The ApoB/ApoA1 ratio is a validated biomarker reflecting the balance between atherogenic and anti-atherogenic lipoproteins. ApoB represents the total number of atherogenic particles (including LDL, VLDL), while ApoA1 is the main protein in HDL, which is protective. A higher ApoB/ApoA1 ratio indicates a predominance of atherogenic lipoproteins and a higher risk for ca
APOE Genotype Risk Index (E2/E3/E4 variants): Explanation and Clinical Context The Apolipoprotein E (APOE) gene has three major alleles: E2, E3, and E4. The combination of these alleles determines an individual's genotype, which significantly influences lifetime risk for Alzheimer's disease and cardiovascular outcomes. E2 allele is generally protective, E3 is neutral, and E4 increases risk, particularly in homozygous
APRI (AST to Platelet Ratio Index): Explanation and Clinical Context The APRI score is a non-invasive index to predict the presence of liver fibrosis and cirrhosis, originally validated in patients with chronic hepatitis C. It is calculated using the formula: [(AST / Upper Limit of Normal AST) / Platelet Count (10^9/L)] × 100. Lower values (<0.5) indicate minimal or no fibrosis, intermediate values (0.5–1.5) suggest
Explanation and Clinical Context The Academic Research Consortium high bleeding risk construct was developed to provide a standardized binary definition of bleeding risk in patients undergoing percutaneous coronary intervention and receiving dual antiplatelet therapy. It organizes clinical characteristics into major and minor criteria that are based on expected one year incidence of serious bleeding events. Major cri
The audited source currently returns an empty page. This catalog entry is retained for coverage and monitoring, but no clinical content or calculation is asserted.
Explanation and Clinical Context The Berlin Criteria provides a standardized method to diagnose acute respiratory distress syndrome based on the degree of hypoxemia, the requirement of positive end expiratory pressure, and the presence of bilateral opacities not fully explained by cardiac failure. The PaO2 FiO2 ratio defines the severity group. A ratio of three hundred or less with mandatory positive end expiratory p
ARDS Severity Index (PaO₂/FiO₂): Explanation and Clinical Context The ARDS Severity Index uses the ratio of arterial oxygen partial pressure (PaO₂) to fractional inspired oxygen (FiO₂) to stratify patients with acute respiratory distress syndrome according to severity. A PaO₂/FiO₂ ratio >300 mmHg indicates no ARDS; 201-300 mmHg indicates mild ARDS; 101-200 mmHg indicates moderate ARDS; < 100 mmHg indicates severe ARD
ARIC Diabetes CVD Score: Explanation and Clinical Context The ARIC Diabetes CVD Score is a validated risk assessment tool to estimate the 10-year risk of cardiovascular disease in adults with type 2 diabetes. It was derived from the Atherosclerosis Risk in Communities (ARIC) study cohort and incorporates patient-specific variables including age, sex, systolic blood pressure, total cholesterol, HDL cholesterol, smokin
ARIC Hypertension Risk Model: Explanation and Clinical Context The ARIC Hypertension Risk Model is a validated tool developed from the Atherosclerosis Risk in Communities (ARIC) Study to estimate the 5-year risk of developing hypertension in middle-aged adults. It incorporates multiple clinical variables including age, sex, race, body mass index (BMI), smoking status, physical activity level, diabetes status, and cho
Aristotle Basic Complexity Score (ABCS): Explanation and Clinical Context The Aristotle Basic Complexity Score is a validated tool designed to estimate the procedural complexity for congenital heart surgery in pediatric and adult patients. It combines factors such as the type of surgical procedure, patient age, presence of noncardiac congenital abnormalities, and genetic abnormalities. Each factor is assigned a weigh
Aristotle Basic Complexity Score (ABCS): Explanation and Clinical Context The Aristotle Basic Complexity Score is a validated tool designed to estimate the procedural complexity for congenital heart surgery in pediatric and adult patients. It combines factors such as the type of surgical procedure, patient age, presence of noncardiac congenital abnormalities, and genetic abnormalities. Each factor is assigned a weigh
Aristotle Comprehensive Complexity (ACC) Score: Explanation and Clinical Context The ACC Score is designed to quantify the overall surgical complexity in congenital heart surgery by combining the Aristotle Basic Complexity (ABC) score with procedure-dependent modifiers and patient-dependent modifiers. The ABC score (range ~1.5 to 15) itself is derived from three domains: potential mortality, potential morbidity, and
Aristotle Comprehensive Complexity Score (CCS): Explanation and Clinical Context The Aristotle Comprehensive Complexity Score (CCS) is a validated scoring system designed to quantify the overall complexity of congenital heart surgery procedures. It integrates patient-related factors (e.g., comorbidities, age, weight), procedure-related factors (e.g., technical difficulty, expected mortality), and diagnosis-related fa
ARISTOTLE HF Subgroup Outcome Index: Rationale and clinical context The original ARISTOTLE trial (apixaban vs warfarin) and its biomarker substudies showed that age, a clinical history of heart failure, and circulating biomarkers — notably NT-proBNP, high-sensitivity cardiac troponin, and growth differentiation factor-15 (GDF-15) — were among the strongest predictors of death and heart-failure related events in patie
Appraisal of Risk in AF (ARISTOTLE-based) Score: Explanation and Clinical Context The ARISTOTLE-based risk score for atrial fibrillation was developed from the ARISTOTLE trial population to predict 1-year risk of stroke or systemic embolism in patients with AF. The model is based on easily obtainable clinical variables including age, prior stroke or transient ischemic attack (TIA), hypertension, diabetes mellitus, an
Arrhythmogenic Left Ventricular Cardiomyopathy (ALVC) Score: Explanation and Clinical Context ALVC Score is a validated risk prediction tool for patients with arrhythmogenic left ventricular cardiomyopathy, aimed at estimating the risk of arrhythmic events over a 5-year period. It incorporates key clinical and imaging parameters, including age, sex, presence of non-sustained ventricular tachycardia (NSVT), left ventr
Arterial Blood Gas Interpretation: Explanation and Clinical Context This tool provides a structured approach to identify the primary acid base disturbance and to assess whether the observed respiratory or renal compensation is appropriate for a single predominant disorder. The algorithm first classifies the sample as acidemia or alkalemia based on pH. It then uses the relationship between pCO2 and HCO3 to identify a
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) Risk Calculator (ESC 2022): Explanation and Clinical Context This tool estimates the 5-year risk of ventricular arrhythmias in patients diagnosed with ARVC based on the ESC 2022 risk model (Cadrin-Tourigny J, et al., Eur Heart J. 2022;43:1664–1678). The model incorporates age, sex, right ventricular dysfunction, history of non-sustained ventricular tachycardia, n
ARVC Screening Probability in Athletes: Explanation and Clinical Context This calculator assists sports cardiologists in assessing pre-test probability for arrhythmogenic cardiomyopathy (ARVC/ACM) in athletes using key signals: family history and characteristic ECG abnormalities. A first-degree relative with confirmed ARVC or a pathogenic variant markedly raises pre-test suspicion. Similarly, young-age sudden cardiac
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) Task Force Criteria (2010 Revised): Explanation and Clinical Context The ARVC Task Force Criteria (2010 revised) is a structured diagnostic tool used to improve diagnostic accuracy for ARVC, a genetic cardiomyopathy characterized by fibro-fatty replacement of the right ventricular myocardium, leading to arrhythmias and sudden cardiac death. The criteria are divid
About the : The ASCVD (Atherosclerotic Cardiovascular Disease) 10-Year Risk Estimator is a predictive tool developed by the American College of Cardiology (ACC) and the American Heart Association (AHA) to estimate the probability of a first cardiovascular event (myocardial infarction, stroke, or cardiovascular death) over the next 10 years. It is based on pooled cohort equations derived from large-scale U.S. populati
Atherosclerotic Cardiovascular Disease (ASCVD) Risk for BP Control Target: Explanation and Clinical Context The ASCVD Risk Score estimates the 10-year risk of atherosclerotic cardiovascular events, including myocardial infarction, stroke, and cardiovascular death, based on the Pooled Cohort Equations developed by the ACC/AHA 2013 guidelines. It incorporates patient-specific factors including age, sex, race, total cho
ASCVD-DM Subscore: Explanation and Clinical Context The ASCVD-DM Subscore is a clinical tool designed to estimate the 10-year risk of atherosclerotic cardiovascular disease (ASCVD) specifically in patients with type 2 diabetes mellitus. It incorporates traditional ASCVD risk factors such as age, sex, total cholesterol, HDL cholesterol, systolic blood pressure, antihypertensive treatment, smoking status, and diabetes
ASCVD-Hypertension Submodel: Explanation and Clinical Context The ASCVD-Hypertension Submodel is a validated tool developed by the American College of Cardiology/American Heart Association to estimate the 10-year risk of atherosclerotic cardiovascular disease (ASCVD) in patients with hypertension. It incorporates demographic factors (age, sex, race), lipid profile (total cholesterol, HDL cholesterol), systolic blood
ASD Closure Complication Risk (TEE-based Model): Explanation and Clinical Context This tool integrates TEE-derived anatomical predictors associated with adverse outcomes during transcatheter secundum ASD closure, translating them into a structured heuristic for clinical use. The strongest predictor for erosion is the coexistence of aortic rim deficiency and device oversizing > 5 mm. Additional features—multiple rim d
ASPECTS (Alberta Stroke Program Early CT Score): Explanation and Clinical Context The Alberta Stroke Program Early CT Score (ASPECTS) is a 10-point quantitative CT-based scoring system designed to detect and quantify early ischemic changes within the middle cerebral artery (MCA) territory on non-contrast head CT. The MCA territory is divided into ten defined regions (four subcortical: caudate head [C], lentiform nucl
Recommendations for Cardiac Chamber Quantification by Echocardiography in Adults: An Update from the ASE and EACVI (2015) Recommendations for the Evaluation of LV Diastolic Function by Echocardiography: An Update from the ASE and EACVI (2016) ASE recommendations for the evaluation of LV diastolic function by echocardiography: Quick reference (2016)
AST/ALT Ratio (De Ritis Ratio): Explanation and Clinical Context The AST/ALT ratio, also known as the De Ritis ratio, is a simple but valuable biomarker used in the assessment of liver injury and prognosis. It was first described by Fernando De Ritis in 1957 as the ratio between serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). A ratio less than 1 typically indicates acute hepatocellular inju
Asthma Predictive Index Explanation and Clinical Context The Asthma Predictive Index is a clinical tool developed to identify young children who have recurrent wheezing and who are at higher risk of developing persistent asthma later in childhood. The index is based on the presence of at least three wheezing episodes in one year combined with either one major criterion or two minor criteria. Major criteria include pa
ASTRAL Score: Explanation and Clinical Context The ASTRAL Score is a validated clinical tool designed to predict 90-day functional outcome after acute ischemic stroke. It integrates six key variables available at hospital admission: age, NIHSS stroke severity, time from symptom onset to admission, range of neurological deficit, arterial territory involved, and serum glucose levels. The total score allows stratificati
Atherogenic Index of Plasma (AIP): Explanation and Clinical Context The Atherogenic Index of Plasma (AIP) is calculated as the base-10 logarithm of the ratio of plasma triglycerides (TG) to high-density lipoprotein cholesterol (HDL-C) in mmol/L: log10(TG/HDL-C). It serves as a sensitive marker of plasma atherogenicity and is closely associated with the size of LDL particles, with higher AIP indicating a predominance
: Explanation and Clinical Context This tool is intended to assist clinicians in distinguishing physiological cardiac adaptation in athletes (“athlete’s heart”) from potentially pathological conditions such as hypertrophic cardiomyopathy, dilated cardiomyopathy, or arrhythmogenic right ventricular cardiomyopathy. The score integrates key features from resting ECG (e.g., T-wave inversion, pathological Q waves, bundle
ATRIA Bleeding Score: Explanation and Clinical Context The ATRIA Bleeding Score (Anticoagulation and Risk Factors in Atrial Fibrillation) is a validated risk stratification tool designed to estimate the annual risk of major bleeding in patients with atrial fibrillation (AF) receiving oral anticoagulant therapy. Developed from a cohort of over 13,000 AF patients in the ATRIA study, it incorporates five independent pre