# Preop Eval vs ABG Acid

The clearest difference is monetization model: Preop Eval at free against ABG Acid's paid. Preop Eval also leads on rating (5.0 vs 4.6). ABG Acid's advantage is ratings volume (7 vs 2) and iOS requirement (13.0 vs 16.6). On price, review sentiment, update cadence and ads there is nothing between them.

Both are free to download. Neither carries in-app purchases, so what you see is what you pay.

Preop Eval holds the better App Store score, 5.0 against 4.6. Both are backed by a comparable volume of ratings — 2 and 7 respectively. Written reviews point the same way: 67% of Preop Eval's written reviews are positive against 63% of ABG Acid's.

Preop Eval ships an update every 6 months, ABG Acid every 5 months. The most recent releases landed on September 30, 2026 and October 16, 2026 respectively.

## The numbers

| Metric | Preop Eval | ABG Acid |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[5.0 (2 ratings)](https://appshunter.io/ios/app/preop-eval/id374154834/reviews)** | [4.6 (7 ratings)](https://appshunter.io/ios/app/abg-acid-base-eval/id426019807/reviews) |
| Number of ratings | 2 | **7** |
| Positive reviews | **66.7% of reviews** | 63.0% of reviews |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 6 months | **Every 5 months** |
| Monetization | **Free** | Paid |
| Size | 15 MB | 1 MB |
| Requires iOS | 16.6 | **13.0** |
| Devices | iPhone | **iPhone, iPod** |
| Age rating | 17+ | 17+ |
| Developer | [United Health Services, Inc.](https://appshunter.io/developer/1451318916) | [Joshua D. steinberg](https://appshunter.io/developer/374154837) |

## What reviewers say

### Preop Eval

[App page](https://appshunter.io/ios/app/preop-eval/id374154834)

This app provides guidance for evaluating and preparing adult patients for non-cardiac surgery. It includes algorithms and resources on medication management, cardiac event timing, and preoperative testing, serving as both a reference and a teaching tool for medical professionals.

**Highlights:** Cardiac evaluation algorithm, Medication guidance (starting/stopping), Surgery timing after cardiac events, Preoperative testing recommendations, Review for students and residents, Perioperative insulin management

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases:** none


### ABG Acid

[App page](https://appshunter.io/ios/app/abg-acid-base-eval/id426019807)

This app guides clinicians through analyzing ABGs and electrolytes to identify acid-base disorders and diagnostic ideas for ill patients. It teaches a stepwise thinking process and provides differential diagnoses with explanations, aiding patient care and clinician learning.

**Highlights:** Stepwise ABG and electrolyte analysis, Identifies acid-base disorders, Provides diagnostic ideas, Teaches critical thinking process, Includes differential diagnoses mnemonics, Calculates predicted pCO2 and corrected bicarbonate

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is Preop Eval free?

Preop Eval is free to download, with no in-app purchases.

### Is ABG Acid free?

ABG Acid is free to download, with no in-app purchases.

### Which has better reviews, Preop Eval or ABG Acid?

Preop Eval is rated higher. Preop Eval averages 5.0 out of 5 from 2 ratings, while ABG Acid averages 4.6 from 7 ratings.

### Do Preop Eval or ABG Acid have ads?

Neither Preop Eval nor ABG Acid shows ads.

### Which is updated more often, Preop Eval or ABG Acid?

Preop Eval ships an update every 6 months, and ABG Acid every 5 months. Most recently, Preop Eval was updated on September 30, 2026 and ABG Acid on October 16, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*