Medical calculators are used millions of times a day. A nurse calculates a heparin drip rate. An ER physician scores a Glasgow Coma Scale. A nephrologist checks an eGFR. Each of these calculations has a formula behind it -- and that formula has a story.
At MDTools.org, we believe every medical formula deserves a citation. Here's why, and how we approach it.
The Problem with "Trust Me" Calculators
Many medical calculator websites show you a result without telling you where the formula came from. That's dangerous in medicine. A doctor should be able to:
- Verify the formula against the original publication
- Check the study population -- was the formula validated for their patient?
- Know the limitations -- every formula has edge cases
How We Handle Citations
Every calculator on MDTools includes:
Original Research Papers
For example, our eGFR Calculator cites the CKD-EPI 2021 equation from Inker et al. (NEJM, 2021). The MELD Score references Kamath et al. (Hepatology, 2001) and the 2016 MELD-Na update.
Clinical Guidelines
Our CHA2DS2-VASc Calculator references the ESC/ACC guidelines for atrial fibrillation management. The ASCVD Risk Calculator cites the 2013 ACC/AHA Pooled Cohort Equations.
Textbook References
For lab reference values, we cite Tietz Clinical Chemistry and Molecular Diagnostics, the gold standard reference:
- Creatinine Normal Ranges -- Tietz 7th edition ranges by age and sex
- Bilirubin Levels -- Direct vs indirect, neonatal ranges
- CRP Levels -- hs-CRP cardiovascular risk stratification
- Potassium Levels -- Critical values and clinical context
- Sodium Levels -- Hypo/hypernatremia workup
- Albumin Levels -- Nutritional and hepatic assessment
- Calcium Levels -- Corrected calcium and ionized calcium
- Chloride Levels -- Acid-base interpretation
- BNP Levels -- Heart failure diagnosis cutoffs
- ALP Levels -- Hepatobiliary vs bone sources
Drug Dosing: Where Citations Matter Most
Drug dosing calculators have the highest stakes. A wrong dose can kill. Here's how we handle it:
Weight-Based Protocols
- Heparin Dosing -- Based on the Raschke et al. weight-based nomogram
- Vancomycin AUC Calculator -- Based on 2020 ASHP/IDSA/SIDP consensus guidelines
- Ketamine Dosing -- Emergency and procedural sedation protocols
Titration Schedules
- Semaglutide Dosing -- FDA-approved Ozempic and Wegovy titration schedules
- Warfarin Dose Adjustment -- INR-based protocol per CHEST guidelines
- Insulin Dose Calculator -- ADA Standards of Care
Pediatric Dosing
- Infant Tylenol Dosing -- Weight-based with AAP guidelines
- Amoxicillin Pediatric Dosing -- AOM, pharyngitis, and pneumonia protocols
The Technical Side
Our citation approach is simple:
- Each calculator page has a "Formula Details" section with the mathematical formula
- Below that, a "References" section with full citations
- A "Formula last verified" date so users know when the formula was last checked
- An FAQ section addressing common clinical questions
We also use Schema.org FAQPage markup so that Google can show our clinical Q&As directly in search results.
Specialized Calculators
Beyond the basics, we've built tools for specific clinical scenarios:
- Corrected Calcium -- Payne formula for albumin adjustment
- Anion Gap Calculator -- With delta-delta ratio
- Creatinine Clearance -- Cockcroft-Gault with IBW adjustment
- Free Water Deficit -- For hypernatremia correction
- Sodium Correction -- Katz correction for hyperglycemia
- QTc Calculator -- Bazett, Fridericia, Framingham, and Hodges formulas
- NIHSS Calculator -- Stroke severity scoring
- SOFA Score -- Sequential organ failure assessment
- Child-Pugh Score -- Hepatic function classification
Multilingual Access
Medical knowledge shouldn't have a language barrier. Every tool is available in German as well as English, with more languages planned.
Open Source = Auditable
The entire codebase is open source on GitHub. Anyone can:
- Verify our formulas against the cited papers
- Submit corrections if they find an error
- Suggest new calculators
In medicine, "where did you get that number?" isn't a rude question -- it's the most important one. Every calculator should be able to answer it.
Check out MDTools.org -- all 100+ tools are free, forever.
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