Clinical Laboratory & Diagnostics Aug 16, 2026 · 6 min read

Serum Creatinine Test: The Primary Marker for Glomerular Filtration Rate

Learn about the Jaffe kinetic method for measuring serum creatinine. A vital test for estimating GFR and monitoring both acute kidney injury and chronic kidney disease.

1. Abstract & Brief Introduction

The serum creatinine test measures the level of creatinine in the blood. Creatinine is a waste product generated from muscle metabolism (breakdown of creatine phosphate). Since it is produced at a relatively constant rate and is almost entirely excreted by the kidneys, it serves as a highly reliable indicator of renal (kidney) function and Glomerular Filtration Rate (GFR).

2. Test Objectives

Assess and monitor overall kidney function (acute kidney injury or chronic kidney disease).
Calculate the estimated Glomerular Filtration Rate (eGFR).
Monitor the effects of nephrotoxic medications (e.g., certain antibiotics, chemotherapy).
Screen for renal impairment before diagnostic imaging that uses contrast media.

3. Method Principle (Jaffe Kinetic Reaction)

The most common method for creatinine determination is the Jaffe Kinetic Method.
In an alkaline medium, creatinine reacts with picric acid (picrate) to form an orange-red colored Janovski complex. The rate of formation of this colored complex is directly proportional to the creatinine concentration. By taking two absorbance readings at specific time intervals (e.g., 30s and 90s) at 510 nm, the interference from slow-reacting non-creatinine chromogens (like protein and ketones) and fast-reacting chromogens (like acetoacetate) is minimized.

Creatinine + Picric Acid ⟶ Creatinine-Picrate Complex (Orange-Red)

4. Laboratory Equipment

Automated Chemistry Analyzer or Spectrophotometer (measuring at 510 nm or 492-546 nm)

Micropipettes (100 µL, 1000 µL) and disposable tips

Cuvettes (1 cm optical path)

Incubator or water bath (37°C)

Clinical centrifuge

5. Reagents & Stability

Reagent 1 (R1): Sodium Hydroxide (Alkaline buffer)
Reagent 2 (R2): Picric Acid
Creatinine Standard (usually 2.0 mg/dL)
Working Reagent: Mix equal volumes of R1 and R2 before use (stable for a few days at room temp).

6. Sample & Pre-analytical Protocol

Parameter	Details & Protocol
Specimen	Serum or Heparinized Plasma. 24-hour urine can also be tested (must be diluted 1:50 first).
Container	Plain tube (red top) or SST (yellow top).
Stability	Serum creatinine is stable for 7 days at 2-8°C, and several months if frozen at -20°C.
Interferences	Hemolysis and lipemia can interfere with absorbance. High bilirubin levels can cause falsely low results (negative interference).

7. Complete Step-by-Step Procedure

Step	Action & Execution
Step 1	Bring the working reagent, standard, and serum samples to room temperature.
Step 2	Set up two cuvettes: Standard and Test.
Step 3	Pipette 1000 µL (1 mL) of the working reagent into both cuvettes.
Step 4	Add 100 µL of Standard to the Standard cuvette, and 100 µL of serum to the Test cuvette.
Step 5	Mix immediately and start the stopwatch.
Step 6	Read the first absorbance (A1) at exactly 30 seconds at 510 nm.
Step 7	Read the second absorbance (A2) exactly 2 minutes (120 seconds) after the first reading.
Step 8	Calculate ΔA = A2 - A1. (Concentration = [ΔA Test / ΔA Standard] × Standard Concentration).

8. Result Interpretation

Finding	Clinical Significance
Elevated Creatinine	Impaired renal function, acute kidney injury (AKI), chronic kidney disease (CKD), urinary tract obstruction, muscle necrosis.
Decreased Creatinine	Low muscle mass (elderly, severe malnutrition, amputation), severe liver disease, normal pregnancy.
BUN / Creatinine Ratio > 20	Suggests pre-renal azotemia (dehydration, heart failure).

9. Reference Ranges

Parameter	Normal Range
Adult Males	0.7 - 1.3 mg/dL (62 - 115 µmol/L)
Adult Females	0.6 - 1.1 mg/dL (53 - 97 µmol/L)
Children	0.3 - 0.7 mg/dL

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Mohammad Sulieman Ibrahim

Full Stack Developer & Writer

Serum Creatinine Test: The Primary Marker for Glomerular Filtration Rate

By Mohammad Sulieman

https://medblog.seeha.tech/posts/baaritaanka-creatinine-ta-dhiigga-calaamadda-koowaad-ee-sifeynta-kilyaha

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1. Abstract & Brief Introduction

2. Test Objectives

Assess and monitor overall kidney function (acute kidney injury or chronic kidney disease).
Calculate the estimated Glomerular Filtration Rate (eGFR).
Monitor the effects of nephrotoxic medications (e.g., certain antibiotics, chemotherapy).
Screen for renal impairment before diagnostic imaging that uses contrast media.

3. Method Principle (Jaffe Kinetic Reaction)

Creatinine + Picric Acid ⟶ Creatinine-Picrate Complex (Orange-Red)

4. Laboratory Equipment

Automated Chemistry Analyzer or Spectrophotometer (measuring at 510 nm or 492-546 nm)

Micropipettes (100 µL, 1000 µL) and disposable tips

Cuvettes (1 cm optical path)

Incubator or water bath (37°C)

Clinical centrifuge

5. Reagents & Stability

Reagent 1 (R1): Sodium Hydroxide (Alkaline buffer)
Reagent 2 (R2): Picric Acid
Creatinine Standard (usually 2.0 mg/dL)
Working Reagent: Mix equal volumes of R1 and R2 before use (stable for a few days at room temp).

6. Sample & Pre-analytical Protocol

Parameter	Details & Protocol
Specimen	Serum or Heparinized Plasma. 24-hour urine can also be tested (must be diluted 1:50 first).
Container	Plain tube (red top) or SST (yellow top).
Stability	Serum creatinine is stable for 7 days at 2-8°C, and several months if frozen at -20°C.
Interferences	Hemolysis and lipemia can interfere with absorbance. High bilirubin levels can cause falsely low results (negative interference).

7. Complete Step-by-Step Procedure

Step	Action & Execution
Step 1	Bring the working reagent, standard, and serum samples to room temperature.
Step 2	Set up two cuvettes: Standard and Test.
Step 3	Pipette 1000 µL (1 mL) of the working reagent into both cuvettes.
Step 4	Add 100 µL of Standard to the Standard cuvette, and 100 µL of serum to the Test cuvette.
Step 5	Mix immediately and start the stopwatch.
Step 6	Read the first absorbance (A1) at exactly 30 seconds at 510 nm.
Step 7	Read the second absorbance (A2) exactly 2 minutes (120 seconds) after the first reading.
Step 8	Calculate ΔA = A2 - A1. (Concentration = [ΔA Test / ΔA Standard] × Standard Concentration).

8. Result Interpretation

Finding	Clinical Significance
Elevated Creatinine	Impaired renal function, acute kidney injury (AKI), chronic kidney disease (CKD), urinary tract obstruction, muscle necrosis.
Decreased Creatinine	Low muscle mass (elderly, severe malnutrition, amputation), severe liver disease, normal pregnancy.
BUN / Creatinine Ratio > 20	Suggests pre-renal azotemia (dehydration, heart failure).

9. Reference Ranges

Parameter	Normal Range
Adult Males	0.7 - 1.3 mg/dL (62 - 115 µmol/L)
Adult Females	0.6 - 1.1 mg/dL (53 - 97 µmol/L)
Children	0.3 - 0.7 mg/dL

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I am Mohammad Sulieman, a Full Stack Developer & Writer. Let's connect and build something amazing together.

hello@sulieman.dev +252 61 500 0000 https://medblog.seeha.tech

Serum Creatinine Test: The Primary Marker for Glomerular Filtration Rate

1. Abstract & Brief Introduction

2. Test Objectives

3. Method Principle (Jaffe Kinetic Reaction)

4. Laboratory Equipment

5. Reagents & Stability

6. Sample & Pre-analytical Protocol

7. Complete Step-by-Step Procedure

8. Result Interpretation

9. Reference Ranges

10. Clinical Comment & Limitations

Comments

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Mohammad Sulieman Ibrahim

Serum Creatinine Test: The Primary Marker for Glomerular Filtration Rate

1. Abstract & Brief Introduction

2. Test Objectives

3. Method Principle (Jaffe Kinetic Reaction)

4. Laboratory Equipment

5. Reagents & Stability

6. Sample & Pre-analytical Protocol

7. Complete Step-by-Step Procedure

8. Result Interpretation

9. Reference Ranges

10. Clinical Comment & Limitations

Did you find this helpful?