Calculators.

Winters formula predicts the PaCO2 the lungs should reach to compensate for a primary metabolic acidosis. Comparing the measured PaCO2 against the expected range tells you whether compensation is appropriate or a second respiratory disorder is present.

Five equally-weighted criteria score community-acquired pneumonia severity from 0 to 5, stratifying 30-day mortality risk and informing whether a patient can be managed as an outpatient or needs admission.

NEWS2 aggregates seven routine observations into a single score that standardises how acute deterioration is detected and escalated in adults. Each parameter scores 0 to 3; the total, together with any single parameter scoring 3, determines a low, medium, or high clinical response.

Eight clinical criteria for patients in whom PE is being considered but gestalt pretest probability is already low. If none of the eight are present, PE can be excluded without D-dimer or imaging. Any single positive criterion means PERC cannot exclude PE and further work-up is required.

Three rapidly-assessed criteria identify patients with suspected infection who are at higher risk of in-hospital death or prolonged ICU stay. A score of 2 or more should prompt escalation, lactate measurement, and a full sepsis assessment. qSOFA is a prompt, not a diagnosis of sepsis and not a screening replacement.

Seven weighted clinical criteria estimate the pretest probability of pulmonary embolism. The result can be read three-tier (low, moderate, high) or two-tier (PE unlikely at 4 or less, PE likely above 4), which guides whether D-dimer or direct imaging is the next step.

The 2013 ACC/AHA Pooled Cohort Equations estimate the 10-year probability of a first hard atherosclerotic cardiovascular event (nonfatal MI, coronary death, or fatal/nonfatal stroke) in adults aged 40 to 79 without known ASCVD. This is a legacy equation: current AHA materials position PREVENT as the race-free tool for contemporary primary-prevention risk estimation.

A weighted score (0 to 9) that refines stroke risk in non-valvular atrial fibrillation beyond the older CHADS2 schema, adding vascular disease, age 65 to 74, and female sex. It identifies the low-risk patients who can safely avoid anticoagulation and stratifies everyone else.

A simple bedside score (0 to 9) estimating the 1-year risk of major bleeding in atrial fibrillation patients on antithrombotic therapy. Its main value is highlighting reversible bleeding risk factors, not vetoing anticoagulation in patients who need it.

A five-domain score (0 to 10) for adults presenting to the emergency department with chest pain, estimating the 6-week risk of major adverse cardiac events (MACE: death, MI, or coronary revascularisation). Low scorers can often be discharged early; high scorers warrant an early invasive strategy.

The QT interval shortens as heart rate rises, so it is corrected to a standard rate (QTc) before judging whether repolarisation is prolonged. This tool reports both the Bazett correction (the long-standing clinical default) and the Fridericia correction (more stable at extreme heart rates). Per the AHA/ACCF/HRS statement, a QTc at or above 450 ms in men or 460 ms in women is prolonged, and a QTc at or above 500 ms marks a substantially increased risk of torsades de pointes.

A seven-item bedside score (0 to 7) for unstable angina or NSTEMI that estimates the 14-day risk of a composite of all-cause death, new or recurrent myocardial infarction, and severe recurrent ischaemia requiring urgent revascularisation. Higher scores identify patients who derive more benefit from an early invasive strategy and potent antithrombotic therapy.

Percent total body weight loss expresses change in weight as a fraction of starting weight. It is the standard way to monitor and report response to obesity treatment, including GLP-1 and dual incretin therapies. A loss of 5% or more is generally considered clinically meaningful, with greater benefit at 10% and 15% or more. It is a monitoring metric, not a diagnosis.

Estimated average glucose (eAG) converts an HbA1c percentage into the average glucose it corresponds to, expressed in the same units patients see on a meter (mg/dL or mmol/L). It comes from the ADAG study regression. eAG is a population-level estimate of average glucose over the preceding 2 to 3 months, not a substitute for actual glucose monitoring, and it should not be confused with the CGM-derived glucose management indicator (GMI).

HOMA-IR is a simple fasting surrogate for insulin resistance derived by Matthews and colleagues in 1985. A healthy reference individual scores about 1; higher values suggest more insulin resistance. There is no single universal threshold: cutoffs vary with the insulin assay, population, age, and BMI, so the number is best read against your own laboratory's reference range and trended over time.

A simple 5-point score (0 to 5) for early risk stratification in acute pancreatitis, predicting in-hospital mortality within the first 24 hours. Each criterion scores 1 point. A score of 3 or more identifies substantially higher mortality and organ-failure risk.

A pre-endoscopy score (0 to 23) using blood urea, haemoglobin, systolic blood pressure, pulse, and clinical features to predict the need for intervention (transfusion, endoscopic therapy, or surgery) in acute upper gastrointestinal bleeding. A score of 0 (some use up to 1) identifies very-low-risk patients who may be considered for outpatient management.

BMI is weight in kilograms divided by height in metres squared. It is a quick population screen for weight status, not a measure of body fat or health on its own. For people of South Asian and other Asian ancestry, risk rises at lower BMIs, so the lower WHO Asia-Pacific cut points are shown alongside the standard bands.

The anion gap (sodium minus chloride and bicarbonate) screens for and characterises metabolic acidosis. Because albumin is the main unmeasured anion, a low albumin masks a real gap, so this tool also reports an albumin-corrected value.

About 40% of total calcium is albumin-bound, so a low albumin lowers measured total calcium without changing the physiologically active ionised fraction. This tool adjusts total calcium for albumin in US or SI units. Where accuracy is critical, measure ionised calcium directly.

Mean arterial pressure estimates the average pressure driving blood to the organs across the cardiac cycle. Because diastole lasts longer than systole, it is weighted toward the diastolic pressure. A MAP of around 65 mmHg is a commonly cited floor for adequate organ perfusion in resuscitation.

A weighted risk assessment model that totals individual venous thromboembolism risk factors (worth 1, 2, 3, or 5 points each) to place a surgical patient into a risk category from very low to high. The category guides whether mechanical prophylaxis, pharmacological prophylaxis, or both are appropriate, always balanced against bleeding risk.

A weighted score that stratifies hospitalised medical (non-surgical) patients by venous thromboembolism risk. A total of 4 or more identifies high risk: in the derivation cohort these patients had a markedly higher VTE rate, and pharmacological thromboprophylaxis is recommended unless contraindicated. A score below 4 is low risk.

A clinical prediction rule that places a patient with suspected deep vein thrombosis into a pretest-probability category. The modern two-level version (DVT likely vs unlikely) is paired with D-dimer: an unlikely score plus a negative D-dimer can safely defer or avoid ultrasound. It is a triage tool, not a stand-alone rule-out.

A non-invasive index using AST (relative to its upper limit of normal) and platelet count to estimate liver fibrosis. WHO hepatitis B guidance uses APRI greater than 2 to identify cirrhosis in adults in resource-limited settings; lower cutoffs (around 0.5 and 1.5) are used to rule out or rule in significant fibrosis, with the usual sensitivity and specificity trade-offs.

The Child-Pugh score grades cirrhosis severity from five variables (bilirubin, albumin, INR, ascites, and encephalopathy), each scored 1 to 3. The total of 5 to 15 maps to Class A, B, or C, which correlates with survival and surgical risk and is still widely used in hepatology.

A non-invasive index combining age, AST, ALT, and platelet count to estimate the likelihood of advanced hepatic fibrosis, widely used as the first step in triaging chronic liver disease before elastography or biopsy.

The Maddrey discriminant function (mDF) grades the severity of alcohol-associated hepatitis from the prothrombin time prolongation and total bilirubin. A value of 32 or above identifies severe disease with high short-term mortality and is the classic threshold for considering corticosteroid therapy.

MELD-Na adds serum sodium to the classic MELD model (bilirubin, INR, creatinine), capturing the prognostic weight of hyponatraemia in cirrhosis. It estimates 90-day mortality and was used by OPTN for liver allocation from 2016 until MELD 3.0 superseded it.

Four clinical criteria (tonsillar exudate, tender anterior cervical nodes, fever by history, absence of cough), each worth 1 point, plus the McIsaac age adjustment, estimate the likelihood of group A streptococcal pharyngitis and frame the decision to test or treat.

The Cockcroft-Gault equation estimates creatinine clearance in mL/min from age, body weight, sex, and serum creatinine. It predates BSA-indexed eGFR equations and is not adjusted to 1.73m2, but it remains the estimate referenced in many drug labels, so it is still used for renal dose adjustment.

High glucose pulls water out of cells into plasma, diluting the measured sodium so it reads lower than the patient's true sodium status. Correcting for glucose estimates the sodium that would be seen at a normal glucose. This tool reports the correction with both the original Katz factor (1.6 per 100 mg/dL above 100) and the later Hillier factor (2.4 per 100 mg/dL above 100); the headline value uses 2.4.

The 2021 CKD-EPI creatinine equation estimates glomerular filtration rate from serum creatinine, age, and sex, dropping the race coefficient used in earlier versions. The result is reported per 1.73m2 of body surface area and maps onto the KDIGO GFR categories used to stage chronic kidney disease.

FENa is the percentage of filtered sodium that ends up in the urine. In oliguric acute kidney injury a value below 1% points to prerenal azotemia (kidneys avidly reabsorbing sodium in response to hypoperfusion), while a value above 2% suggests intrinsic tubular injury such as acute tubular necrosis. It was derived in selected oliguric patients and is unreliable in several common situations, most notably diuretic use.

A 7-point score (0 to 7) estimating the 2-day risk of stroke after a transient ischaemic attack, from age, blood pressure, clinical features, symptom duration, and diabetes. Higher scores predict higher early stroke risk, but current guidance increasingly favours urgent specialist assessment and imaging over the score alone.

The Glasgow Coma Scale grades consciousness across best eye opening (1 to 4), verbal response (1 to 5), and motor response (1 to 6) for a total of 3 to 15. It is the standard way to describe and track impaired consciousness; a total of 8 or less is severe and should prompt consideration of airway protection.

A standardised 15-item neurological examination that grades acute stroke severity from 0 to 42. It is the common language for stroke trials and care: it helps gauge severity, informs reperfusion and triage decisions, and lets a deficit be tracked reproducibly over time.

The Mifflin-St Jeor equation estimates resting energy expenditure (the calories burned at rest) from weight, height, age, and sex. Multiplying by an activity factor gives total daily energy expenditure, a starting point for calorie planning in healthy adults.

The Devine formula estimates ideal body weight from sex and height, the basis many drugs use for weight-based dosing instead of actual weight. Adjusted body weight blends ideal and actual weight (correction factor 0.4) for drugs that partly distribute into excess tissue.

The A-a gradient is the difference between the calculated alveolar oxygen tension and the measured arterial oxygen tension. A gradient that is normal for age suggests hypoventilation or a low inspired oxygen tension (such as altitude), whereas a widened gradient points to V/Q mismatch, right-to-left shunt, or impaired diffusion. The expected upper limit rises with age, roughly (age / 4) + 4 mmHg on room air at sea level.

Calculated serum osmolality is estimated from sodium, glucose, and urea (BUN). When a measured osmolality is available, the osmolar gap (measured minus calculated) screens for unmeasured osmoles. A large gap with metabolic acidosis raises concern for toxic alcohols (methanol, ethylene glycol).