Clinical Guides And Calculator Articles
Evidence-based medical calculator guides, clinical scoring tutorials, and decision-support articles from the Quick Medical Calculator editorial team.
All articles
Reticulocyte Results: Percentage, Absolute Count and Production Index
Before interpreting "reticulocytes 9", establish what the laboratory reported. A percentage, an absolute cell count and a calculated production index are different quantities. None becomes more informative by losing its label or units in a handover.A Due-Date Calculation Is Not the Final Obstetric Estimate
Calendar arithmetic can produce an estimated due date quickly. The clinical task is to establish and document the best obstetric estimate, not to let each new calculator result overwrite the existing record.Urine ACR: Do Not Confuse Albumin Concentration With the Ratio
Urine albumin concentration and the albumin-creatinine ratio are related but different results. The ratio uses urine creatinine to account for differences in urine concentration. A change in albumin concentration alone should not be described automatically as a proportional change in albuminuria.The Same Shock Index Can Describe Different Patients
Shock index compresses heart rate and systolic blood pressure into a ratio. That can make a pattern easier to notice, but the compression also discards information. The original observations should remain visible whenever the ratio is reported.P/F Ratio: A Fraction, a Pressure and the Missing Clinical Context
A worked P/F ratio example explains the difference between fraction-based arithmetic and the calculator's oxygen-percentage input.Light's Criteria: One Positive Condition Is Enough
Light's criteria are not a majority vote. The biochemical classification is exudative when any one of the three conditions is positive. Counting how many are positive can help check the calculation, but it does not turn the rule into a two-out-of-three threshold or a severity scale.Body Surface Area: Check the Measurement Before Reusing the Number
Body surface area is often copied between records because the final number looks simple. Its usefulness depends on the measurements, formula and units behind it. A plausible-looking BSA is not evidence that those details were checked.Corrected Sodium in Hyperglycaemia: An Estimate, Not a Correction Target
An estimated sodium adjusted for hyperglycaemia is not a second laboratory measurement. It is a model-based way to consider the effect of glucose-associated water shifts. Calling it "corrected" should not make it a target concentration or a prescription for correcting the measured sodium.A Growth Percentile Describes a Reference, Not a Target
"The child is on the 25th percentile" leaves several questions unanswered. Which measurement, reference population, chart version, age and sex were used? Without them, a percentile is difficult to reproduce and easy to misinterpret.Measured Osmolality, Calculated Osmolarity and the Gap Between Them
A measured serum osmolality and a calculated estimate are not two measurements of the same kind. The laboratory measures osmolality per kilogram of solvent. A concentration-based equation estimates osmolarity; clinical reports and calculators often call the estimate "calculated osmolality". Keep that distinction in mind when subtracting them.A Low Calcium-Creatinine Clearance Ratio Is a Clue, Not a Diagnosis
A calcium-creatinine clearance ratio, or CCCR, can contribute to assessment of familial hypocalciuric hypercalcaemia (FHH) versus primary hyperparathyroidism. The useful question is not simply whether the result is below a line. First ask whether the specimens and units make the ratio interpretable.Four QTc Results From One Tracing: What Changed?
Two QTc values can disagree even when the measured QT and heart rate are identical. Before calling the difference a physiological change, identify the correction formula. Comparing a Bazett value with a Fridericia value is not a like-for-like trend.Suspected DKA: Check Which Ketone Was Measured and When
"Ketones positive" is an incomplete laboratory description. It may refer to a urine dipstick or to a quantitative blood beta-hydroxybutyrate...Pregnancy Weight Change: State the Starting Measurement and Gestational Age
A pregnancy record may contain a recalled pre-pregnancy weight, a measured booking weight and several later measurements. Subtracting each starting...A Thyrotoxicosis Score Cannot Settle the Cause of Acute Deterioration
Acute deterioration in someone with thyrotoxicosis demands clinical assessment, not a contest between a score and the examination. A score may help...NEXUS and Canadian C-Spine Rules: One Eligible Pathway, Not a Hybrid Checklist
Two cervical-spine rules can contain familiar clinical ideas without being interchangeable. Selecting reassuring features from each does not create a...Apgar Scores: Time-Stamped Observations, Not an Individual Prognosis
An Apgar total without its assessment time is an incomplete record. A total without the surrounding clinical observations and interventions can also be...The Canadian CT Head Rule Begins With Eligibility, Not Addition
The first question in a head-injury decision rule is whether the presentation belongs to the population the rule studied. A person outside that...Rapid Shallow Breathing Index: Record How It Was Measured
This article concerns adults receiving mechanical ventilation, matching the scope of the AARC guideline discussed below. An RSBI is a description of a...An ICH Score Is Not an Individual Futility Decision
A severity score can help clinicians describe an intracerebral haemorrhage consistently. It becomes dangerous when that description is transformed into...Glucose Infusion Rate: State the Concentration, Time Basis and Weight
A pump setting describes fluid volume per unit time. Glucose infusion rate, or GIR, describes glucose mass delivered per kilogram per minute. The two...MASCC Does Not Turn Febrile Neutropenia Into an Automatic Discharge Decision
The words "lower risk" describe a model classification, not a complete care arrangement. In febrile neutropenia, confusing those meanings can make an...DIC Scores Need a Version, a Clinical Context and Repeat Assessment
"DIC score 4" is not a complete clinical statement. The reader needs to know which criteria were used, whether the required observations were available...Neonatal Bilirubin: Age in Hours and the Selected Guideline Belong Beside the Result
"Bilirubin 210 on day two" is not enough information for a neonatal handover. It leaves the unit, exact postnatal age, measurement method, gestational...MIPI: Keep WBC Units, the LDH Reference and Model Version Together
A white cell count of 8.4 and one of 8,400 may describe the same blood sample. In a logarithmic prognostic model, entering the wrong representation...Metabolic Syndrome: Record the Definition Instead of Treating Every Label as Equivalent
"Metabolic syndrome present" looks like a simple binary statement. In practice, it is incomplete unless the definition and the measurements used are...TTKG: Check the Assumptions Before Trusting the Estimate
The transtubular potassium gradient, or TTKG, illustrates a limitation that unit checks alone cannot solve. Its arithmetic can be reproduced exactly...A VBAC Prediction Is Not a Birth-Options Decision
"VBAC calculator" is not a sufficiently precise description of a result. Different tools use information available at different stages, were developed...ABCD2 Is Not a Waiting-Time Rule for Suspected TIA
When neurological symptoms have resolved, the absence of a current deficit can make the encounter feel less urgent. That impression must not be...ECOG and Karnofsky: Describe Function Before Attempting a Crosswalk
Two notes can describe the same person using different performance-status scales without permitting an exact numerical conversion. The first task is to...Heart-Failure Stage, Functional Limitation and Prognostic Risk Are Different Questions
A stage letter, a functional class and a predicted probability are not three ways of expressing one number. Each preserves a different part of a...Paediatric Maintenance Fluids Are Not a Resuscitation Calculation
A maintenance calculation answers a narrow question: what baseline water volume does a stated weight-based model estimate over a day? It does not...Duke Treadmill Score: Keep Exercise Time, ECG Units and Symptoms Together
An exercise-test report contains more than a duration and an ECG measurement. The protocol, the interpretability of the tracing and the reason exercise...Urea Reduction Ratio: Sampling Can Change the Apparent Result
Urea reduction ratio, or URR, compares concentrations before and after a haemodialysis session. The equation is short: 100 x (1 - post/pre). The...BUN-Creatinine Ratio: First Establish What the Laboratory Reported
A ratio can be arithmetically correct and still describe the wrong quantities. That is particularly easy when one report lists urea in mmol/L and...Free Water Deficit: An Estimated Volume Is Not a Replacement Plan
The free-water-deficit equation produces a volume, but a volume is not a complete fluid prescription. It does not specify a route, fluid composition,...mg, mg/kg and mg/m2 Are Not Interchangeable Instructions
A dose-normalisation basis is part of the instruction, not an optional display preference. An amount in mg is already an absolute mass. An amount in...What a Medicine Half-Life Estimate Leaves Out
“Five half-lives” sounds like a clock-based answer, but it is only meaningful after identifying the quantity being modelled and the assumptions behind...Infusion Pump Rate and Gravity Drip Rate Are Different Quantities
An infusion rate is not fully specified by a number. “50” could mean millilitres per hour or drops per minute, and those are different quantities....The Same Milligram Dose, Two Different Liquid Strengths
A liquid-medicine handover is incomplete if it preserves only the number of millilitres. Volume is tied to concentration. A replacement bottle can...Dose Per Administration or Dose Per Day? Check the Denominator
An adult medicine instruction can contain a perfectly legible number and still leave the intended quantity unclear. The problem is often the...Calculating ANC Without Losing a Factor of 1,000
The neutrophil percentage and the absolute neutrophil count answer different questions. A percentage describes the differential; the absolute count also depends on how many white cells are present. Reading one as the other can conceal an important result.An Incidental FIB-4 Result: Check the Framework Before the Category
A FIB-4 result can help organise further liver assessment. It cannot tell you that a person has a particular histological fibrosis stage. Before interpreting an incidental result, establish why it was calculated and which population-specific pathway is being used.GOLD 2026 Versus 2024: Updating a COPD Review Without Mixing Guideline Eras
Compare historical GOLD 2024 advice with the 2026 framework: why one exacerbation matters, why initial and follow-up treatment differ, and why eosinophils do not prescribe an inhaler.GOLD and BODE in COPD: Airflow Limitation Is Not Exercise Prognosis
Use GOLD and BODE for different clinical questions. Compare two fictional patients with identical FEV1, check six-minute walk inputs, and avoid deterministic survival or transplant decisions.GOLD COPD Assessment in 2026: Diagnosis, Spirometric Grade and Exacerbation Group
Separate COPD diagnosis, FEV1 airflow-limitation grade and the 2026 A/B/E framework. A worked example explains why moderate obstruction and lower dyspnoea do not cancel exacerbation risk.HbA1c, HOMA-IR and Insulin Calculators: Three Different Questions, Three Safety Checks
Check HbA1c reliability, interpret estimated average glucose without missing hypoglycaemia, and distinguish HOMA1 from HOMA2. Calculator arithmetic cannot choose a safe insulin dose.Paediatric Early Warning Scores: Use the Local System, Not a Universal PEWS Threshold
PEWS variants are not interchangeable. A fictional ward scenario shows why oxygen context, trends and parental concern matter even with a low score, and why escalation must follow the approved local pathway.CHA2DS2-VASc: Why the Same Number Can Mean Different Things
How US and European AF frameworks interpret the same score differently, without turning risk estimates into drug or dose instructions.DAS28: Check the Inputs Before Interpreting the Trend
Check DAS28 version, joint counts and input units before interpreting a trend or considering a treatment change.Ottawa Rules: Choose the Correct Region Before Ordering an X-Ray
Apply ankle, foot and knee imaging rules to the right region, population and examination.Centor and McIsaac: A Testing Decision, Not an Antibiotic Prescription
Use sore-throat scores to guide testing, interpret negative child RADTs and avoid score-only antibiotic decisions.Caprini: Turn a Risk Total Into a Documented Prevention Plan
Interpret a versioned Caprini score alongside the operation, bleeding risk and local prevention pathway.AUDIT and AUDIT-C: What to Do With a Positive Screen
Interpret positive alcohol screens without diagnosing dependence from a score or mixing questionnaire versions.Endocrine Calculators: Three Results That Need Context Before Action
Interpret thyroid tests, nodule surveillance thresholds and adjusted calcium with their clinical limits.Bishop Score: What a Cervical Assessment Can and Cannot Decide
Distinguish cervical readiness from the indication for induction, and interpret NICE's boundary of six.RCRI: Why a Higher Score Does Not Automatically Mean a Stress Test
Check RCRI inputs and historical risk estimates before deciding whether preoperative testing would change care.FRAX: Read the Two Probabilities Without Adding Them
Interpret overlapping fracture probabilities and US treatment thresholds without adding risks or replicating FRAX.HOMA-IR: Check the Units, Then Resist the Diagnostic Shortcut
Check paired fasting samples, HOMA1 units and population limits without turning a result into a diagnosis.Glasgow-Blatchford Score: Why Two Is Not the Routine Discharge Cutoff
Check GBS units and distinguish the guideline outpatient boundary from a historical study cutoff.NIHSS: A Low Score Can Still Represent a Disabling Stroke
Recognise disabling stroke despite a low NIHSS, and separate scoring accuracy from treatment eligibility.Wells Score for PE: Keep the Probability Rule and D-Dimer Pathway Together
Keep Wells probability categories, D-dimer units and the selected PE diagnostic pathway together.Kidney Calculators: First Decide Whether the Problem Is Acute or Chronic
Distinguish timed AKI changes from established CKD before choosing a kidney-function tool.Low FENa in AKI: Sodium Retention Is Not a Fluid Prescription
Interpret low FENa and FEUrea cautiously without assuming dehydration or fluid responsiveness.AF Follow-Up: Rhythm Improvement and Stroke Prevention Are Different Decisions
Separate rhythm improvement from stroke prevention, including the limits of newer post-ablation trials.qSOFA: A Warning Score, Not a Sepsis Rule-Out Test
Recognise qSOFA's screening limits and distinguish a warning score from sepsis and septic-shock criteria.MELD and Child-Pugh: What Does Each Score Leave Out?
MELD, Child-Pugh and ACLF assessments answer different questions. Learn why recurrent ascites and clinical deterioration can matter despite a modest laboratory score.CKD-EPI 2021: Checking an eGFR Result Before Acting
Check CKD-EPI 2021 inputs, reproduce an adult eGFR example and interpret chronicity, muscle-mass bias and medication thresholds without turning an estimate into a prescription.CURB-65 or PSI: Which Pneumonia Decision Are You Making?
Separate pneumonia place-of-care decisions from organ-support assessment, and see how a cancer-weighting error can move a fictional PSI result into the wrong class.CURB-65: A Bedside Calculation With Important Boundaries
Work through exact CURB-65 boundaries, distinguish urea from BUN and connect the result to clinical assessment rather than automatic admission or antibiotic instructions.PHQ-9: Interpreting a Positive Screen and a Changing Score
Interpret a PHQ-9 screen and changing score without confusing screening with diagnosis, percentage of baseline with improvement, or symptom severity with a safety assessment.Cardiology Calculators: Start With the Clinical Question
Choose a cardiology tool by its clinical question, endpoint, time horizon and model version, including the 2026 move to PREVENT-ASCVD for eligible primary prevention.APACHE II: Why a Severity Score Is Not a Mortality Percentage
Audit APACHE II component mapping, collection windows and missing observations, and distinguish a severity total from an individual hospital-mortality probability.Suspected PE: Where PERC, Wells, Geneva, and D-Dimer Fit
Place PERC, Wells, Geneva and D-dimer in the right diagnostic sequence, with a fictional age-adjusted FEU example and explicit eligibility and residual-risk limits.DVT Wells Score: Do Not Lose a Point or Lose the Follow-Up
See how a missing previous-DVT point changes the two-level Wells pathway, and why a negative proximal scan may still need an arranged follow-up test.Glasgow Coma Scale: Document the Response, Not Just the Total
Document Glasgow Coma Scale components, confounders and changes, including untestable verbal responses, without turning an incomplete examination into a total.HEART, TIMI, and GRACE: Three Different Chest-Pain Questions
Distinguish acute chest-pain evaluation from TIMI and GRACE prognosis, and avoid treating an isolated low HEART score or early troponin result as a completed pathway.Did Kidney Function Change, or Did the eGFR Equation Change?
Audit an eGFR trend across a laboratory-equation change and distinguish indexed from absolute estimates before inferring kidney injury, recovery or a dosing decision.CHA2DS2-VASc: Three Scoring Errors Worth Catching
Catch age double-counting, repeated counting of stroke history and altered sex-point totals, using fictional component audits rather than another anticoagulation-threshold table.Pediatric Calculators: Three Checks Before Trusting the Output
Match paediatric growth references and clinical-rule eligibility, then work through a fictional liquid-dose calculation that separates mg/kg/day from mg/kg/dose.Nutrition Calculators: An Estimate Is a Starting Point, Not a Meal Prescription
Reproduce a fictional BMI and resting-energy estimate, examine activity assumptions and weight trajectory, and recognise when ordinary calorie calculators cannot guide feeding.SOFA in Sepsis: Count All Six Systems and Compare With Baseline
Check all six original-SOFA systems, reproduce a fictional total and baseline change, and distinguish Sepsis-3 assessment from qSOFA screening and SOFA-2.Ten Emergency Decision Tools: Check Eligibility Before the Result
Check eligibility and the next diagnostic step before using ten emergency tools, including a fictional anticoagulated head-injury example where routine rule-out reassurance fails.ABG Interpretation: Do Not Let a Normal-Looking Number End the Assessment
Use fictional blood-gas and chemistry examples to avoid normal-pH reassurance and recognise how low albumin can obscure an anion gap without substituting for lactate testing.Understanding a MELD Result: Five Details to Confirm
Confirm a MELD result's version, laboratory units, dates and dialysis convention, and separate allocation priority from an individual survival forecast or referral decision.