Ask the doctor: I got an amber warning on my blood test results. Should I be worried?

​Dr Grant replies: It is most likely that you have excellent kidney function. Your creatinine is the toxin in the blood stream your kidney needs to filter out. This is the gold standard kidney blood test and yours is well within normal range. An elevated creatinine blood test is often the first indication of kidney damage. As yours is a low normal, there is no need to worry.

Creatinine is derived from the metabolism of creatine in skeletal muscle and from dietary intake of cooked meat (animal protein). Variations in creatinine levels exist due to high or low muscle mass, creatine supplement intake, patients with advanced liver/heart failure, amputations or neuromuscular disease, or those with a high-protein/vegan/vegetarian diet.

One of the main problems with interpreting blood test results is that patients can often misinterpret the data. This is one of the reasons why I am not a fan of the green/amber/red light system in some blood test reporting. It takes a lot of time to explain each biochemical number to patients and GP’s generally don’t have the time to go through it in detail. To be honest, even when attempting to explain numbers to patients, they can become overwhelmed and often don’t understand what the doctor is trying to say.

The urea is below the average ‘range of normal’ — however, this is highly unlikely to be of any clinical concern in the setting of a normal creatinine and in a healthy, well patient. In fact, it is an elevated urea blood test that would cause some concern, but only if the creatinine is also elevated.

Urea is your marker for hydration and a low urea tends to mean you drink plenty of water (including milk and decaffeinated drinks) on a daily basis. A high urea, in the setting of a normal creatinine tends to mean clinical dehydration. Symptoms of kidney disease include reduced urination or absence of urination, blood in the urine or even brown urine, new onset swelling in the feet/ankles, lack of appetite, vomiting, fatigue and shortness of breath.

Urea, creatinine, and uric acid are some of the waste products of metabolism that the kidney must excrete in the urine. The kidney must constantly adjust the amount of urine to match the overall intake and endogenous production of these waste products. Amazingly, the kidney also excretes a number of hormones, calcium, phosphorus, and vitamin D3 (involved in bone metabolism). This is why patients with chronic kidney disease may present with anaemia, and urine samples are often tested to ensure the kidney is not allowing protein or blood to escape as this may be a sign of kidney disease.​

The most common causes of chronic kidney disease are poorly controlled diabetes mellitus and hypertension. Both of these conditions can often go undetected for many years (with the exception of type1 diabetes) which is why they are screened for during routine blood testing. Other causes include obesity, infections, cancer treatments, certain medicines can damage the kidney, and some autoimmune conditions

If you have a family history, you need to be extra diligent and ensure you undertake a regular check-up. Thankfully, blood pressure is easy and more accurate to check in a home setting, and everyone should be encouraged to check their blood pressure at home, up to three days per week.

Dr Jennifer Grant is a GP with Beacon HealthCheck