Cataract surgery is one of the most common operations in the world. It usually takes less than half an hour, and most patients go home the same day. Even so, plenty of people are surprised when the eye surgeon hands them a list of blood tests before the operation, and they ask the obvious question: what does my blood have to do with my eye?
More than you’d think. The results can decide when the operation happens, what kind of anaesthetic is used, and how quickly you recover afterwards.
Take an example we see play out often. A man in his sixties, let’s call him Abu Khalid, booked his operation, arranged time off and asked his son to drive him. A few days before the date he had his blood tests, and his HbA1c came back much higher than he expected. He felt perfectly fine, but the surgeon chose to postpone by several weeks until his sugar was under control. It was annoying at the time. It also spared him a real risk of infection or swelling in the retina after surgery. Had he done the tests a month before instead of a few days, the date might never have moved.
This article covers the tests eye surgeons usually ask for, why each one matters, when to have them done, and which medicines your doctor needs to know about.
Why does an eye surgeon need blood tests?
Most people having cataract surgery are over 50, and many have diabetes, high blood pressure or take blood thinners. None of these usually rules out surgery, but they do need to be under control first.
Consultant ophthalmic surgeon Dr Sherif Ekram, who works between the UK and the Middle East in cataract, glaucoma and refractive surgery, points out that the pre-operative assessment is never only about the eye. An eye that is perfectly ready for surgery can still run into trouble afterwards if blood sugar is poorly controlled, or if a bleeding risk went unnoticed.
The main tests before cataract surgery
1. HbA1c (average blood sugar)
For people with diabetes, this is the most important test. It reflects your average blood sugar over the past two to three months, not just today’s reading.
A high HbA1c is linked to a greater risk of infection after surgery, slower healing, and swelling at the centre of the retina (macular oedema). If it is very high, the surgeon may postpone until it improves.
2. Fasting or random blood glucose
This is often checked on the day of surgery or shortly before, to make sure your sugar isn’t so high or so low that it affects the safety of the procedure.
3. Complete blood count (CBC)
This picks up anaemia, low platelet counts and signs of an active infection. An infection elsewhere in the body before surgery can raise the risk of it reaching the eye.
4. Clotting tests (PT and INR)
Essential if you take a medicine such as warfarin. Most modern cataract operations use local anaesthetic and a very small incision, so many patients don’t need to stop their blood thinner. Your INR does need to be within the range your doctor sets. Never stop a blood thinner without talking to the doctor who prescribed it.
5. Kidney function and electrolytes
These may be requested for older patients or people with diabetes or high blood pressure, especially if the operation involves general anaesthetic or medicines given through a drip.
6. Hepatitis screening
Some hospitals test for hepatitis B and C before any surgical procedure as part of routine theatre safety. It has nothing to do with the eye itself, and depending on the hospital you may not be asked for it at all.
Do I need to fast before the tests?
This is one of the questions we hear most. It depends on the test:
- HbA1c: no fasting needed, any time of day is fine.
- Fasting blood glucose: fast for 8 to 10 hours beforehand. Water is allowed.
- CBC, clotting tests and kidney function: usually no fasting needed.
If you’re having several tests in one visit and one of them is fasting glucose, the easiest option is to come in the morning before breakfast and get them all done at once.
Medicines your doctor needs to know about
Blood tests are only part of the picture. Some medicines that seem to have nothing to do with the eye can affect how the operation goes, so write down everything you take and bring the list to your appointment.
Prostate medicines, tamsulosin being the best known, are among the most important to mention. They can make the iris floppy during surgery, even if you stopped taking them a long time ago. When the surgeon knows in advance, they can prepare tools and techniques that reduce the problem.
Blood thinners such as aspirin, clopidogrel, warfarin and the newer anticoagulants. Most patients stay on them, but the decision belongs to your eye surgeon together with the doctor who prescribed them.
Diabetes medicines and insulin, particularly if you’ve been asked to fast on the day. Ask specifically about your morning dose. Skipping instructions here can lead to a drop in blood sugar.
Herbal supplements, because some increase the tendency to bleed. Many people leave them off the list because they don’t think of them as medicines.
What about patients with glaucoma?
Glaucoma doesn’t usually call for extra blood tests on its own. It does change how the surgeon plans the operation. They may combine cataract removal with a procedure to lower eye pressure in the same sitting, and they will choose the lens implant with more care.
Dr Sherif Ekram’s view is that the stage of the glaucoma decides the surgical plan, and that some multifocal lenses may not suit an eye whose optic nerve is already affected, because they slightly reduce contrast. You can read more about his approach to planning cataract surgery alongside glaucoma, and how he plans treatment for both conditions together.
When should you have the tests?
Dr Sherif Ekram advises patients not to leave their tests until the last minute. An unexpected sugar or clotting result can mean postponing the operation after you’ve already arranged time off and someone to go with you. Getting the timing right gives your doctor room to adjust treatment and keep the date.
- HbA1c: two to four weeks before surgery, so there’s time to adjust treatment if needed.
- CBC and kidney function: within the two weeks before surgery.
- INR: one to three days before, or as your doctor instructs.
Bring your results to the clinic, and if possible have them all done at the same laboratory so your doctor can compare them easily with your previous results.
Frequently asked questions
Are the tests different if the surgery uses a laser?
Usually not. The tests relate to your general health, not to the technique the surgeon uses.
What if one of my results is abnormal?
Don’t panic. Many abnormal results can be corrected within a few weeks, for example by improving sugar control or adjusting a blood thinner dose. Send the result to your doctor, who will decide whether it means postponing.
Do I need an ECG?
It may be requested for older patients or anyone with a history of heart disease, especially if general anaesthetic is a possibility. It’s a separate check from the lab tests.
Can I use results from two months ago?
An HbA1c may be accepted if it’s fairly recent, but most surgeons want the blood count and clotting tests from within two weeks of surgery. Ask the clinic how recent your results need to be.
The bottom line
Pre-operative tests for cataract surgery aren’t a box-ticking exercise. They’re how you make sure your body is ready, the operation goes safely, and recovery is quicker.
You can have all your pre-operative tests done at any Delta Medical Laboratories branch, book a home sample collection on WhatsApp, and follow your results in the Delta app.
أكتوبر الوردي — شهر التوعية بسرطان الثدي
دقيقتان قد تفرق كثيراً: قيّمي مؤشرات الخطورة لديك مجاناً
هذا التقييم استبيان توعوي أولي، وليس تشخيصاً طبياً ولا بديلاً عن استشارة الطبيب.
