Over the past few years, tech and health-care companies have demonstrated that Apple's (NASDAQ:AAPL) iPhone has plenty of potential as a portable medical device.

Beyond being a phone, the iPhone is a powerful ultraportable computer with a touchscreen, onboard cameras, a microphone, and motion sensors. Those features make it a viable replacement for the brains of many modern medical devices -- allowing for the creation of much cheaper and smaller systems.

Let's look at five surprising medical uses for the iPhone, and some familiar companies that are associated with these new uses, such as Sanofi (NASDAQ:SNY), Microsoft (NASDAQ: MSFT), Qualcomm (NASDAQ:QCOM), and Google (NASDAQ:GOOGL).

The iPhone as a glucose meter

Diabetes patients have to check their blood sugar levels regularly with glucose meters. These devices traditionally require a pinprick to dip a blood sample onto a strip of glucose paper, which is then inserted into the glucose meter to be measured.

Sanofi recognized that the iPhone and the iPod Touch could be used as replacements for traditional glucose meters, since many patients already carries them around on a regular basis. In 2011, the FDA approved Sanofi's iBGStar, a small dongle that attaches to the bottom of either device and reads compatible test strips.

The device is then used like a regular glucose meter, but the accompanying app on the smartphone is considerably smarter than traditional devices -- it automatically synchronizes the blood glucose readings over the Internet, giving the user an accurate record of reference that can be shared with others.

The iPhone as a blood pressure monitor

The Withings Blood Pressure monitor connects an external blood pressure cuff to the iPhone, turning the iPhone into a control panel for the device. It is also compatible with the iPod Touch and the iPad.

The monitor also automatically records the readings, dates them, and keeps an accurate log of previous blood pressure readings to share with other people.

The device also comes with the option to store the collected data in Microsoft's electronic health records service, HealthVault, which health-care professionals can access.

The iPhone as a portable ECG device

Last December, the FDA approved AliveCor, a device that turns the iPhone into an ECG/EKG (electrocardiograph) reader. The device attaches to the back of the iPhone to read and record a patient's heart rate via an app.

The $100 device, invented by Oklahoma cardiologist David Albert, can be used to conduct a regular ECG test to assess cardiac problems, such as rhythmic disturbances. The device was recently ported to Google Android and has also been approved for veterinary use.

The low cost of the device and widespread availability of smartphones make the AliveCor an ideal device for treating patients on the field in developing countries. By comparison, a lower-end ECG system can cost roughly $1,200.

Qualcomm is a major investor in AliveCor, which is in line with the tech giant's stated long-term goals of merging technology with medicine. In August, Qualcomm and Palomar Health started Glassomics, an idea incubator focused on focusing on the development of new portable and wearable health-care devices, with a specific focus on Google Glass and smartphones.

The iPhone as a dermatologist

Smartphone cameras are improving at a breakneck pace. Although the 8-megapixel camera on the iPhone 5S still doesn't hold a candle to Nokia's whopping 41 megapixels on its Lumia 1020, the iPhone's camera is more than powerful enough to analyze photos of skin problems.

A major advantage that smartphones have over traditional cameras is that they can analyze photos and attempt to match the photo to similar ones in color, size, and shape through programmed algorithms. In addition, the photos can be documented in detail for future reference and shared with others.

This makes it a highly useful tool for diagnosing skin problems. For example, FotoFinder has released the Handyscope Dermatoscope, an attachable case and lens which provides 20x magnification for the iPhone's camera for close-up shots of moles and other skin conditions. The device doesn't actually scan and analyze the moles -- it documents them and maps them out on a virtual patient.

The App Store has plenty of other apps that try to scan for cancerous moles through algorithms and digitally sent photos. However, trials have shown that these apps can be wrong up to 30% of the time, so they shouldn't be considered reliable replacements for professional dermatologists just yet.

The iPhone ultrasound

Last but not least, the iPhone can also be used as an ultrasound device.

Mobisante's MobiUS SP1 ultrasound system for the iPhone was approved in 2011. Like the other devices mentioned in this article, the MobiUS is an attachable ultrasound device which uses the iPhone as a display and record keeping device.

Traditional ultrasound machines can cost from $10,000 to $200,000, while the MobiUS system costs between $7,000 and $8,000.

Therefore, Mobisante's smaller and cheaper device could be a very attractive product for rural areas and developing countries, since ultrasounds are necessary for a wide variety of medical conditions, such as cardiovascular and gastrointestinal problems.

The Foolish takeaway

These devices and apps only represent the tip of the iceberg for the medical uses of the iPhone and other smartphones. However, it's easy to notice a recurring theme here -- by connecting devices to the iPhone, companies can make cheaper, cloud-connected medical devices that allow for easier backup and sharing of accumulated patient records.

However, Google Glass could change all of that in the near future. These devices could also be connected to Google Glass via Bluetooth, and could even become more convenient because of Glass' hands-free form factor.

In closing, dear readers -- what other jaw-dropping medical uses of the iPhone do you think will be popular in the future? Please share your ideas in the comments section below!