1,329 calculators and references across 60 specialties, with formula confidence shown up front.
Absolute and Relative Risk Reduction Explanation and Clinical Context Absolute Risk Reduction ARR represents the difference in event rates between a control group and an experimental group. ARR quantifies how much an intervention reduces risk in absolute terms and is directly interpretable in clinical practice. Relative Risk Reduction RRR represents the proportional decrease in risk relative to the baseline risk of t
ACEF Score: Explanation and Clinical Context The ACEF Score (Age, Creatinine, and Ejection Fraction) is a simple, validated risk prediction tool for short-term mortality in patients undergoing cardiac surgery or coronary interventions. It is calculated using the formula: ACEF = Age / LVEF + 1 (if serum creatinine > 2 mg/dL). Higher scores indicate higher risk of adverse outcomes. It is particularly useful in preopera
AFEQT Score (Atrial Fibrillation Effect on Quality of Life): Explanation and Clinical Context The AFEQT Score is a validated patient-reported outcome measure that assesses health-related quality of life in patients with atrial fibrillation (AF). It evaluates four domains: Symptoms, Daily Activities, Treatment Concern, and Overall Health. Each domain is scored from 0 to 100, where higher scores indicate better quality
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
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 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
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
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 Attack rate is an epidemiologic measure used to quantify the proportion of individuals in a population who develop a condition during an outbreak period. It is commonly used in infectious disease investigations to describe the speed and extent of disease spread within a defined group. The calculation compares the number of new cases with the number of individuals who are susceptible o
BMI Based Body Fat Percentage Explanation and Clinical Context BMI based body fat estimation uses body mass index, age, and sex to approximate total body fat percentage. This method is derived from population based regression models and provides a simple alternative when direct body composition measurement is unavailable. Body mass index reflects the relationship between body weight and height but does not differenti
Body Mass Index: Explanation and Clinical Context Body Mass Index is a commonly used anthropometric measure that relates weight to height and provides a general estimation of body fatness. BMI is calculated by dividing weight in kilograms by the square of height in meters. Although BMI does not directly measure adiposity, it is widely adopted because of its simplicity, reproducibility, and strong correlation with var
: Explanation and Clinical Context Body surface area represents the external surface area of the human body and is widely used in clinical medicine because it correlates more closely with physiological parameters compared to actual body weight. BSA is routinely applied in cardiovascular care, nephrology, oncology, and critical care medicine. In hemodynamics, BSA is essential for calculating cardiac index, which is th
: Explanation and Clinical Context Cardiac Index represents the cardiac output normalized to body surface area, allowing clinicians to interpret cardiac performance in a manner that accounts for differences in body habitus. This parameter provides a more individualized assessment of circulatory adequacy compared to cardiac output alone. It is expressed in liters per minute per square meter and is widely used in criti
Explanation and Clinical Context Cardiac Output represents the total blood volume ejected from the ventricles every minute. It is determined by multiplying Stroke Volume and Heart Rate and presented in liters per minute. The value reflects the effectiveness of the cardiovascular system in delivering oxygen and nutrients to tissues. Normal Cardiac Output typically ranges from four to eight liters per minute in healthy
Cardiac Power Output (CPO): Comprehensive Explanation and Clinical Context Cardiac Power Output is a hemodynamic parameter that quantifies the overall pumping capability of the heart by integrating both cardiac output and mean arterial pressure into a single measure. It reflects the amount of hydraulic energy delivered by the heart to circulate blood throughout the body, and it is expressed in Watts. Unlike isolated
CHA₂DS₂-VASc Score: Explanation and Clinical Context The CHA₂DS₂-VASc Score is a validated clinical risk stratification tool used to estimate the annual risk of ischemic stroke in patients with atrial fibrillation (AF), particularly non-valvular AF. It refines the earlier CHADS₂ Score by incorporating additional risk factors—vascular disease, age 65–74 years, and female sex—to improve sensitivity in identifying patie
Cockcroft Gault creatinine clearance estimation Explanation and clinical context The Cockcroft Gault equation provides an estimate of creatinine clearance in milliliters per minute using patient age weight serum creatinine and sex. The formula is CrCl equals open parentheses 140 minus age close parentheses times weight divided by open parentheses 72 times serum creatinine close parentheses. For female patients multip
E/e' Ratio: Explanation and Clinical Context The E over e prime ratio is one of the most widely used echocardiographic indices to estimate left ventricular filling pressure. The E wave represents early diastolic transmitral flow velocity which increases when the left atrial pressure rises. The e prime velocity is measured at the mitral annulus and reflects the intrinsic rate of myocardial relaxation. Since e prime de
About This Calculator Ejection Fraction (EF) menggambarkan persentase darah yang dipompa ventrikel kiri setiap siklus. Perhitungan ini menggunakan rumus: EF = (SV / EDV) × 100. Pada konteks klinis, EF menjadi salah satu indikator utama fungsi sistolik ventrikel kiri. Nilai ≥ 50% dianggap normal, 40–49% menunjukkan mild LV dysfunction, dan < 40% mengarah pada reduced EF yang sering terkait dengan heart failure dengan
Explanation and Clinical Context The Fick principle is one of the most fundamental physiological methods used to determine cardiac output. This calculation is based on the relationship between oxygen consumption and the arteriovenous oxygen content difference. The method assumes that the uptake or release of oxygen by the tissues is equal to the product of blood flow and the arteriovenous oxygen difference. In clinic
Fractional Excretion of Sodium FeNa Explanation and Clinical Context Fractional excretion of sodium FeNa quantifies the percentage of filtered sodium that is ultimately excreted in urine using simultaneously obtained urine and plasma measurements. The formula is FeNa equals Una times Pcr divided by Pna times Ucr all multiplied by one hundred to yield a percentage. FeNa is commonly used to help distinguish reduced ren
Fractional Excretion of Urea FeUrea Explanation and Clinical Context Fractional Excretion of Urea FeUrea estimates the percentage of filtered urea that is excreted in urine. The calculation uses urine urea concentration serum urea concentration urine creatinine concentration and serum creatinine concentration. The formula is FeUrea equals Uurea times Scr divided by Surea times Ucr multiplied by 100 percent. FeUrea co
About Gensini Score: The Gensini Score is a quantitative angiographic tool used to assess the severity of coronary artery disease (CAD). It considers both the degree of luminal narrowing and the importance of the lesion's location in the coronary tree. Each degree of stenosis (1–25% = 1 point; 26–50% = 2; 51–75% = 4; 76–90% = 8; 91–99% = 16; 100% = 32) is multiplied by a weighting factor based on the anatomic segment
Explanation and Clinical Context The Homeostatic Model Assessment for Insulin Resistance is a widely used method to estimate insulin resistance from fasting glucose and fasting insulin levels. The formula is fasting glucose in mg per dL multiplied by fasting insulin in micro IU per mL divided by four hundred five. This indirect method reflects the balance between hepatic glucose output and pancreatic beta cell functi
HOMA-IR (Homeostatic Model Assessment of Insulin Resistance): Explanation and Clinical Context HOMA-IR is a validated index used to estimate insulin resistance based on fasting plasma glucose and insulin levels. The formula is: HOMA-IR = (Fasting Glucose [mg/dL] × Fasting Insulin [µU/mL]) / 405. Higher HOMA-IR values indicate greater insulin resistance. It is commonly used in metabolic and cardiometabolic research an
INTERHEART Risk Score: Comprehensive Explanation and Clinical Context The INTERHEART Risk Score is a globally validated tool developed from the INTERHEART study, which assessed over 30,000 participants across 52 countries. It identifies nine modifiable risk factors responsible for over 90% of myocardial infarction risk worldwide. These include smoking, hypertension, diabetes, abdominal obesity, poor diet, physical in
Left Atrial Volume Index (LAVI): Explanation and Clinical Context LAVI represents the left atrial volume indexed to body surface area and serves as a reliable marker of chronic diastolic burden. Enlargement of the left atrium occurs gradually as a consequence of prolonged elevation of left ventricular filling pressure. Because of this, LAVI is considered a structural biomarker that reflects chronic diastolic dysfunct
Left Ventricular Mass Index (LVMI): Explanation and Clinical Context Left ventricular mass index is a key echocardiographic parameter used to quantify the extent of cardiac structural remodeling associated with pressure or volume overload. The Devereux formula is the most validated method for estimating left ventricular mass using linear measurements obtained from parasternal long axis imaging. The resulting left ven
Sokolow–Lyon Index (SV1 + tallest R in V5 or V6): Explanation and Clinical Context The Sokolow–Lyon Index is a classic electrocardiographic voltage criterion for detecting left ventricular hypertrophy (LVH). It is calculated as the depth of the S wave in lead V1 plus the amplitude of the tallest R wave in lead V5 or V6 (measured in millimetres). A summed value > 35 mm (3.5 mV) is the conventional cut-off suggesting L
Mean Arterial Pressure MAP: Comprehensive Explanation and Clinical Context Mean Arterial Pressure represents the average pressure in the arteries throughout one cardiac cycle. MAP is considered a more reliable indicator of tissue perfusion compared to systolic or diastolic pressure alone because it incorporates both systole and diastole within a single integrated value. The commonly used clinical formula uses one thi
Modified Shock Index (MSI): Explanation and Clinical Context The Modified Shock Index (MSI) is a refinement of the traditional Shock Index (SI), which is defined as the ratio of heart rate (HR) to systolic blood pressure (SBP). MSI replaces SBP with mean arterial pressure (MAP) in the denominator, thereby improving sensitivity and specificity in detecting hemodynamic instability. It is calculated as: MSI = Heart Rate
Control Event Rate CER Experimental Event Rate EER Number Needed to Treat NNT or Number Needed to Harm NNH Explanation and Clinical Context Number Needed to Treat is a measure that reflects how many patients need to receive a specific intervention for one additional patient to benefit compared with control therapy. When the treatment reduces adverse outcomes the absolute risk reduction becomes positive and the result
Oxygen Desaturation Index (ODI): Explanation and Clinical Context Oxygen Desaturation Index (ODI) quantifies the number of oxygen desaturation events per hour of sleep, typically defined as a ≥4% drop in oxygen saturation from baseline, lasting at least 10 seconds. It serves as a non-invasive and practical surrogate for the Apnea–Hypopnea Index (AHI) in evaluating sleep-disordered breathing (SDB). An elevated ODI ref
Pulmonary Vascular Resistance Calculator Explanation and Clinical Context Pulmonary vascular resistance describes the afterload that the right ventricle must overcome to eject blood into the pulmonary circulation. It is derived from a hemodynamic relationship that integrates pressure gradients across the pulmonary vasculature and the magnitude of pulmonary blood flow. PVR reflects the degree of vasoconstriction, remo
Pulse Pressure: Explanation and Clinical Context Pulse pressure is the numerical difference between systolic and diastolic blood pressure. It reflects the interaction between stroke volume, aortic compliance, and ventricular function. A normal pulse pressure in healthy adults is approximately forty millimeters of mercury, although this value may vary with age. A widened pulse pressure may indicate increased arterial
Qp Qs Ratio Calculator Summary and Clinical Context The Qp Qs ratio is a Doppler based calculation used to quantify the relationship between pulmonary blood flow and systemic blood flow. It is an essential parameter when evaluating patients with suspected intracardiac shunts such as atrial septal defect, ventricular septal defect, or patent ductus arteriosus. Doppler echocardiography provides a noninvasive method to
QTc Bazett Formula: Explanation and Clinical Context The QT interval represents the time from the start of ventricular depolarization to the end of ventricular repolarization on an electrocardiogram (ECG). QT interval duration varies with heart rate, and QTc (corrected QT) is calculated to standardize QT for heart rate. Bazett's formula is the most widely used correction: QTc = QT / √RR, where QT is in milliseconds a
QTc Fridericia Correction: Explanation and Clinical Context The Fridericia formula is used to correct the QT interval for heart rate: QTcF = QT / (RR^1/3), where RR is the interval between heartbeats in seconds. It provides a more accurate correction than Bazett's formula, especially at extreme heart rates. QTc prolongation is associated with increased risk of ventricular arrhythmias, including Torsades de Pointes, a
Revised Cardiac Risk Index RCRI Explanation and Clinical Context The Revised Cardiac Risk Index is one of the most widely used bedside tools for estimating the probability of perioperative major adverse cardiac events in patients undergoing non cardiac surgery. The score was derived from a large cohort and validated in multiple populations. It relies on six predictors that represent structural cardiac disease, myocar
Shock Index (HR/SBP Ratio): Explanation and Clinical Context The Shock Index (SI) is a simple, bedside physiological ratio calculated by dividing the heart rate (HR) by the systolic blood pressure (SBP). It serves as a rapid and sensitive indicator of hemodynamic compromise and circulatory shock. A normal Shock Index typically ranges from 0.5 to 0.7. Values above 0.9 are considered abnormal and have been strongly cor
Simpson’s biplane method: explanation, clinical context and references The biplane method of disks (the modified Simpson’s rule) estimates left ventricular end-diastolic and end-systolic volumes from apical 4-chamber and apical 2-ch views; the ejection fraction (LVEF) is then calculated as EF = [(EDV − ESV) / EDV] × 100%. In routine practice the machine may report volumes from each apical view and clinicians commonly
Stroke Volume: Explanation and Clinical Context Stroke volume represents the amount of blood ejected by the left ventricle during each cardiac contraction. The most accurate non invasive method for calculating stroke volume in clinical practice uses pulsed wave Doppler at the left ventricular outflow tract. The calculation requires the cross sectional area of the outflow tract and the velocity time integral of the sy
Stroke Volume Index (SVi): Explanation and Clinical Context Stroke Volume Index is a hemodynamic parameter that describes the amount of blood ejected by the left ventricle during each cardiac contraction, adjusted to body surface area. This index refines the interpretation of stroke volume by incorporating patient size, making it a more accurate indicator of forward flow in individuals with significantly different bo
Systemic Vascular Resistance (SVR): Comprehensive Explanation and Clinical Context SVR represents the resistance encountered by blood as it flows through the systemic circulation. It reflects the interaction between vascular tone, blood viscosity, and vessel diameter. The calculation of SVR is derived from the relationship between perfusion pressure and cardiac output, expressed as the difference between mean arteria
Systemic Vascular Resistance Index (SVRi): Explanation and Clinical Context The systemic vascular resistance index represents the afterload imposed on the left ventricle after correcting for body surface area. It is derived from the transpulmonary pressure gradient, represented by mean arterial pressure minus right atrial pressure, divided by the cardiac index. SVRi provides a more individualized assessment of vascul
TIMI Risk Score for UA/NSTEMI: Comprehensive Explanation and Clinical Context The TIMI (Thrombolysis In Myocardial Infarction) Risk Score is a validated tool used to predict the likelihood of adverse cardiovascular outcomes (death, myocardial infarction, or urgent revascularization) within 14 days in patients with Unstable Angina (UA) or Non ST-Elevation Myocardial Infarction (NSTEMI). It consists of seven clinical p
Urine Sodium Na Urine Potassium K Urine Chloride Cl Urine Anion Gap Explanation and Clinical Context The urine anion gap is a practical bedside calculation that estimates urinary ammonium excretion. It is calculated using the sum of urine sodium and urine potassium minus urine chloride. Ammonium is excreted in association with chloride therefore low chloride relative to sodium and potassium suggests impaired ammonium
Vasoactive-Inotropic Score (VIS): Explanation and Clinical Context The Vasoactive-Inotropic Score (VIS) quantifies the amount of cardiovascular support a patient receives through vasoactive and inotropic medications. It was originally developed to assess post-operative outcomes in pediatric cardiac surgery, correlating higher scores with increased morbidity and mortality. The VIS is calculated as: VIS = dopamine (µg/