Why tablets do not simply “go in and disappear”

When you swallow a medicine, it does not travel straight to the sore joint or the heart and then vanish. Instead, it goes on a journey:

1. It is absorbed from your stomach or gut into the blood.
2. It is processed (changed) mainly by the liver into forms the body can use or get rid of.
3. It is removed from the body, mostly by the kidneys in urine, sometimes also in bile or stool.

The whole time, your body is balancing two needs:

• enough medicine in the blood to help,
• not so much that it builds up and harms.

In later life – when kidney and liver reserves may be lower – this balancing act becomes more delicate. That is why blood tests start to appear more often alongside repeat prescriptions.

Kidneys: your body’s filters

Your kidneys are like two fine filters. With each heartbeat, blood passes through them. Waste products and extra water are filtered into urine; useful things are kept.

Many medicines (or their “used” forms) leave the body through the kidneys. If the kidneys are slower or damaged, those medicines can stay in the body longer and build up to higher levels than intended.

Blood tests that look at kidney function

On your printouts or online record you may see:

• Creatinine: a waste product from muscles. High levels can suggest the kidneys are not clearing waste as well.
• eGFR (estimated glomerular filtration rate): an estimate of how well your kidneys filter blood. It is usually written as a number (for example, 80, 45, 25) with a unit like “mL/min/1.73m²”.
• Sometimes urea and electrolytes (salts) such as sodium and potassium.

eGFR naturally tends to fall with age. A lower number does not always mean disease, but it does mean your team needs to think more carefully about medicine doses and choices.

Why kidney function matters for medicines

Some tablets are cleared mostly by the kidneys. If kidney function is reduced and doses are not adjusted, side effects become more likely – for example:

• stronger or longer-lasting effects from certain painkillers or drugs for heart rhythm,
• build-up of medicines used for diabetes or blood pressure,
• higher risk of harmful blood potassium levels with some heart or kidney tablets.

That is why your GP or pharmacist might say things like “We need to check your kidney function before increasing this” or “At your eGFR, we will use a smaller dose”.

Liver: your body’s chemistry workshop

The liver is a busy processing plant. It:

• changes many medicines into active or “used” forms,
• handles alcohol, hormones and toxins,
• makes important proteins such as those that help your blood clot.

If the liver is inflamed or scarred, it may process medicines more slowly or less predictably. In some cases, the medicines themselves can irritate the liver.

Blood tests that look at liver function

Your records may mention:

• ALT, AST: enzymes that can rise when liver cells are irritated or damaged.
• ALP and GGT: enzymes related to bile flow and certain liver or bone conditions.
• Bilirubin: a yellow pigment that can build up if the liver or bile ducts are not working well.
• Albumin: a protein made by the liver, sometimes lower when liver function is poor or when you are unwell in other ways.

A single slightly abnormal test is often less important than the pattern over time and how you feel. But persistent changes may mean some medicines need review.

Ageing, reserves and “borderline” results

One piece of rare knowledge that is seldom explained is this: test results are not just “good” or “bad”. They sit in the context of your age, size, history and medicines.

In later life, kidneys and liver often have less spare capacity. You might have:

• kidneys that work well enough for daily life but have less room for shocks (such as dehydration, infections, certain medicines),
• a liver that copes day-to-day but becomes more sensitive to alcohol, herbal products or new tablets.

Your team may call this “borderline” or “mild impairment”. It may not make you feel ill at all – but it does change how boldly they can use certain medicines.

Why blood tests appear on your repeat slip

You might see notes such as “bloods due”, “kidney tests required”, or prescriptions held until tests are done. This is not punishment. It is usually because:

• a medicine can affect kidneys or liver and needs regular safety checks,
• your kidneys already work less well and doses must be watched,
• the team has agreed a monitoring plan (for example, every 6–12 months) and the date has arrived.

In other words, a blood test is part of the prescription itself. It helps your clinician see whether the current plan is still safe for your organs.

Joining the dots: dehydration, infection and “acute kidney knocks”

Another quiet truth is that kidney numbers can dip temporarily when you are unwell – for example:

• with vomiting or diarrhoea when you cannot drink enough,
• during serious infections, especially with high temperature,
• when certain medicines for blood pressure, pain or kidneys are combined with dehydration.

Professionals sometimes call this an “acute kidney injury” or “AKI” – a sudden drop in kidney function. In many cases it is reversible if treated promptly (fluids, stopping or adjusting some tablets, treating infection).

If you already have reduced kidney function, you may be given sick-day rules such as “If you are vomiting or have diarrhoea, contact your GP or 111 to check if any tablets should be paused.” Having these written down in advance is helpful.

Questions you are allowed to ask about your results

You do not need to understand every abbreviation, but you are absolutely entitled to clear explanations. Examples of useful questions:

• “Has my kidney function changed over the last few years, or is it stable for my age?”
• “Which of my regular medicines depend on my kidneys working well?”
• “Are any of my tablets hard on the liver, and are my liver tests comfortable with them at the moment?”
• “If my kidney or liver numbers changed suddenly, what symptoms should I watch for?”

It can help to take a pen and write the answers in your own words on your medicines list. Your understanding matters as much as the numbers.

Home and daily life – small ways to protect kidneys and liver

While big treatment decisions belong with your clinicians, there are homely, realistic habits that can quietly support your organs:

• Fluids: within any restrictions your team has set, sip fluids through the day rather than large gulps at night. Dehydration makes medicines “more concentrated” in the blood.
• Caution with painkillers: avoid adding extra over-the-counter painkillers on top of regular ones without checking; some combinations strain kidneys or liver.
• Alcohol: if you drink, keep alcohol within agreed limits for your situation. The liver is already busy with medicines; alcohol is like an extra shift.
• Infections: if you become unwell with fever, vomiting or diarrhoea, seek early advice about whether any tablets should be paused and whether blood tests are needed.
• Home safety: if kidney problems cause swelling or heavy legs, consider chairs with firm arms, good lighting and clear routes to reduce fall risk when you are tired.

How PHAT sessions fit alongside kidney and liver care

PHAT’s role is not to interpret your blood tests, but to:

• give you time and language to make sense of what clinicians say,
• provide gentle movement that supports circulation, balance and mood – all of which help you cope better with long-term conditions,
• create a space where you can say, “My GP mentioned my kidneys – I do not quite understand what that means for my tablets” and not feel rushed.

Used together with your GP, hospital and pharmacy care, this makes you an active partner in protecting the organs that quietly work behind every prescription.