What is Creatinine?

What is Creatinine?

Creatinine is a chemical waste product generated from muscle metabolism and, to a lesser extent, the consumption of meat. It is a critical indicator used by healthcare professionals to assess how well your kidneys are functioning. Under normal conditions, the kidneys filter creatinine from the blood and expel it through urine. When kidney function is impaired, creatinine levels in the blood begin to rise.

How Creatinine Is Produced

Creatinine is the byproduct of creatine phosphate, a compound found in your muscles that helps provide energy for muscle contractions. This process is constant; as long as you have muscle mass and are moving, your body is producing creatinine. Because muscle mass remains relatively stable day-to-day, the rate of creatinine production generally stays consistent for most individuals.

The Role of the Kidneys

The kidneys are the primary filtration system of the body. Their job is to maintain a healthy balance of water, salts, and minerals while removing waste products like creatinine.

Almost all creatinine is filtered by the kidneys and excreted in the urine. This makes it an ideal “marker” (or surrogate) for kidney function: if the kidneys are failing, the “trash” (creatinine) starts to pile up in the bloodstream – i.e the higher the creatinine, the worse the kidney function,

Normal Creatinine Levels

Normal levels vary based on age, biological sex, and body size. Results are reported in SI (micromoles per litre, or µmol/L) or Imperial (mg/dL) units.

• Adult Men: 60 to 120 µmol/L (0.7 to 1.3 mg/dL)

• Adult Women: 50 to 100 µmol/L (0.6 to 1.1 mg/dL)

• Children: 20 to 90 µmol/L (0.2 to 1.0 mg/dL) depending on age and muscle development.

Common Creatinine Tests

To measure this waste product, doctors typically use two main methods:

1. Serum Creatinine Test: A simple blood test that measures the amount of creatinine in your blood at a single point in time.

2. Creatinine Clearance Test: This involves a blood sample and a 24-hour urine collection to compare the creatinine in your blood to the amount excreted in your urine.

What High Creatinine Levels Mean

A high creatinine level is often a red flag for kidney dysfunction. Potential causes include:

• Acute Kidney Injury (AKI): Short-term damage to the kidneys.

• Chronic Kidney Disease (CKD): Long-term damage to the kidneys.

• Dehydration: Lack of fluids can cause a temporary spike.

• High Protein Intake: Consuming large amounts of meat or protein supplements.

• Intense Exercise: Strenuous physical activity can temporarily increase muscle breakdown.

Understanding GFR (Glomerular Filtration Rate)

Doctors don’t look at creatinine in a vacuum. They use your serum creatinine level, along with your age, weight, and sex, to calculate your eGFR (estimated Glomerular Filtration Rate).

The GFR is considered the gold standard for determining your stage of kidney health.

A GFR of 90 ml/min or higher is considered normal, while a GFR below 60 for three months or more may indicate chronic kidney disease (CKD). In other words, unlike creatinine, a higher GFR is better; as it indicates better kidney function.

Symptoms of Elevated Creatinine

If your levels are significantly high, you might experience symptoms related to AKI or CKD, such as:

• Changes in urination frequency or colour.

• Swelling (edema) in the feet, ankles, or around the eyes.

• Fatigue and lethargy.

• Shortness of breath.

• Nausea or a metallic taste in the mouth.

How to Lower Creatinine Levels

Lowering creatinine usually involves addressing the underlying cause – e.g. treat AKI or CKD. You cannot raise or lowr your creatinine easily by lifestyle measures.

When to See a Doctor

Routine blood tests usually include a creatinine test, as part of urea and electrolytes (‘U&E’s).

Early detection is the most effective way to manage kidney health and prevent further complications (e.g. worsening of CKD).

Always consult a doctor to interpret your specific lab results, as ‘normal’ can vary between different laboratories.