Creatinine

Creatinine – Key Information

Creatinine is an organic chemical compound produced as a result of metabolic processes, mainly in the skeletal muscles, as a degradation product of creatine. Creatine is a key energy carrier in muscles, and approximately 1–2% of its total amount is broken down into creatinine each day. This compound is filtered by the kidneys and excreted in the urine, making it an important indicator of kidney function.

Creatinine Test

The laboratory test measuring creatinine levels is used to assess kidney function, diagnose kidney diseases, and monitor treatment. It is also essential before certain diagnostic procedures requiring contrast agents, such as computed tomography or magnetic resonance imaging.

The concentration of creatinine in the serum results from both production and excretion. It depends on muscle mass as well as the excretory function of the kidneys.

The test involves drawing blood from a vein, which is then sent to the laboratory for analysis. The entire procedure takes about 2–3 minutes, while the blood draw itself lasts several seconds. Improper preparation may lead to unreliable results. It is recommended to perform the test in the morning.

When Should You Test Creatinine Levels?

• before diagnostic tests using contrast (e.g., CT scan, MRI);
• preventively once a year, even without symptoms;
• when kidney damage is suspected, including acute or chronic kidney disease;
• when symptoms related to the urinary system occur;
• monitoring patients after kidney transplant;
• in cases of heart failure;
• monitoring hypertension;
• in diabetes;
• during treatment with neurotoxic substances or medications excreted by the kidneys (dose adjustment).

Symptoms that should prompt a creatinine test:

• hematuria, oliguria, or complete urinary retention;
• severe lower back pain;
• changes in the color or smell of urine;
• swelling around the ankles and face (under-eye puffiness);
• fever associated with kidney infections;
• nausea and vomiting;
• general weakness, fatigue, sleepiness;
• difficulty concentrating;
• dry and itchy skin;
• frequent urge to urinate.

High Creatinine

Elevated creatinine levels (above 1.3 mg/dl) often indicate impaired kidney function. Causes of high creatinine include:

• kidney failure,
• acute kidney injury,
• chronic kidney disease,
• low hydration levels or dehydration,
• intense physical activity,
• certain medications that may increase creatinine as a side effect.

Low Creatinine

Low creatinine levels (below 0.6 mg/dl) are generally not a cause for concern and often indicate normal kidney function. Causes may include:

• restrictive diets, especially low-protein diets;
• low muscle mass, especially in older adults or individuals with muscular dystrophy;
• use of certain medications, such as steroids or diuretics;
• pregnancy, due to glomerular hyperfiltration.

If low creatinine levels are detected, it is recommended to consult a doctor for an overall health assessment and possible additional testing.

Learn more:

• Creatinine – what it is, when to test, and reference ranges
• Kidney tests

How to Prepare for a Creatinine Test

You should remain fasting for 8 to 12 hours before the blood draw. The last meal should be eaten no later than 6:00 p.m. on the day before the test. It is recommended to avoid fatty or heavy meals and alcohol, as they may negatively affect the results.

On the day of the test, you may drink a glass of water. It is not recommended to consume coffee, tea, or other beverages. You should also avoid intense physical activity for at least 24 hours before the test.

It is best to perform the test in the morning to obtain the most reliable results.

FT3 Test Results

If the results are abnormal, it is recommended to consult a doctor for proper interpretation.

Check HERE

Reference ranges (may vary between laboratories)

• FT3: usually 2.25–6.0 pmol/l (≈ 1.5–4 ng/l).
• TSH: typically 0.4–4.0 µIU/ml.

How to interpret results in practice?

Test results should always be interpreted together with TSH levels. The combined assessment of FT3 and TSH is crucial, as normal FT3 may coexist with abnormal TSH. This pattern is often characteristic of subclinical hyperthyroidism or hypothyroidism.

Factors That May Affect Test Results

• poor diet,
• alcohol,
• infections.

Who Should You Consult About Abnormal Results?

• Endocrinologist
• Internist