Estimation of Serum Creatinine

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Introduction

  • Estimation of Serum Creatinine is a non-protein nitrogenous waste product formed from creatine phosphate metabolism in skeletal muscle.
  • It is produced at a fairly constant rate depending on muscle mass.
  • Creatinine is freely filtered by the glomeruli and only minimally reabsorbed by renal tubules.
  • Therefore, serum creatinine is one of the most reliable biochemical markers of glomerular filtration rate (GFR).
  • Serum creatinine estimation is routinely used to assess kidney function and monitor renal disease.
  • Increased serum creatinine usually indicates impaired renal filtration.

Principle

  • Serum creatinine estimation is commonly based on Jaffe kinetic method.
  • Creatinine reacts with alkaline picrate to form an orange-red creatinine-picrate complex.
  • The intensity of color formed is directly proportional to creatinine concentration in the sample.
  • Absorbance is measured at 492 nm / 520 nm depending on analyzer.

Reaction

Creatinine + Picric Acid (alkaline medium) → Orange-red Creatinine-Picrate Complex

Method

Two common methods for serum creatinine determination are:

  1. Jaffe’s Reaction:
    • The reaction of creatinine with alkaline picrate produces a reddish-orange color.
    • Interference from proteins, glucose, and other substances is a limitation.
  2. Enzymatic Method:
    • Enzymes (e.g., creatininase) catalyze the conversion of creatinine to intermediates, producing measurable products like ammonia or hydrogen peroxide.
    • These methods are highly specific and less prone to interference.

Specimen

Sample Type

  • Serum is the preferred specimen
  • Heparin plasma may also be used

Precautions

  • Use a non-hemolyzed sample
  • Separate serum early
  • Avoid contamination

Requirements

Materials

  • Patient serum sample
  • Reagents:
    • Picric acid solution (for Jaffe’s method) or enzyme reagents (for enzymatic methods)
    • Alkaline buffer (e.g., sodium hydroxide)
  • Distilled water

Instruments

  • Spectrophotometer or automated biochemistry analyzer
  • Pipettes and cuvettes

Procedure

Components Blank Standard Test
Working reagent 1000 µL 1000 µL 1000 µL
Distilled water 100 µL — —
Standard — 100 µL —
Sample — — 100 µL

Incubation

  • Mix properly
  • Incubate for 30 seconds to 2 minutes depending on kit method

Reading

  • Measure absorbance against blank
  • Read at 492 nm

Calculation

The serum creatinine concentration is calculated using the formula:

Creatinine concentration (mg/dL) = Absorbance of Test / Absorbance of Standard × Standard concentration

Normal Values

  • Adults (Male): 0.7–1.3 mg/dL (62–115 µmol/L)
  • Adults (Female): 0.5–1.1 mg/dL (44–97 µmol/L)
  • Children: 0.3–0.7 mg/dL (26–62 µmol/L)

Clinical Significance

Increased Serum Creatinine

  • Acute kidney injury
  • Chronic kidney disease
  • Glomerulonephritis
  • Dehydration
  • Urinary obstruction

Decreased Serum Creatinine

  • Reduced muscle mass
  • Pregnancy
  • Severe liver disease

Diagnostic Importance

  • Assesses renal function
  • Estimates glomerular filtration rate
  • Monitors kidney disease

MCQs

1. Creatinine is formed from:

A. Glucose
B. Creatine phosphate
C. Urea
D. Cholesterol
Answer: B. Creatine phosphate

2. Creatinine is mainly produced in:

A. Liver
B. Skeletal muscle
C. Kidney
D. Brain
Answer: B. Skeletal muscle

3. Serum creatinine is mainly used to assess:

A. Liver function
B. Kidney function
C. Thyroid function
D. Cardiac function
Answer: B. Kidney function

4. Common method for creatinine estimation:

A. Biuret method
B. Jaffe method
C. GOD-POD method
D. Diazo method
Answer: B. Jaffe method

5. Principle of Jaffe method is reaction with:

A. Urease
B. Picric acid
C. Sulfanilic acid
D. Arsenazo III
Answer: B. Picric acid

6. Creatinine reacts in:

A. Acidic medium
B. Alkaline medium
C. Neutral medium
D. Saline medium
Answer: B. Alkaline medium

7. Color formed in Jaffe reaction:

A. Blue
B. Orange-red
C. Green
D. Yellow
Answer: B. Orange-red

8. Reaction product:

A. Creatinine-picrate complex
B. Azobilirubin
C. Quinoneimine dye
D. Phosphomolybdate complex
Answer: A. Creatinine-picrate complex

9. Wavelength used:

A. 340 nm
B. 405 nm
C. 492 nm
D. 650 nm
Answer: C. 492 nm

10. Preferred sample:

A. Serum
B. Urine only
C. Whole blood
D. Saliva
Answer: A. Serum

11. Plasma anticoagulant preferred:

A. EDTA
B. Heparin
C. Oxalate
D. Citrate
Answer: B. Heparin

12. Creatinine is filtered by:

A. Tubules
B. Glomeruli
C. Liver
D. Spleen
Answer: B. Glomeruli

13. Creatinine reabsorption in kidney is:

A. Complete
B. Minimal
C. High
D. Variable
Answer: B. Minimal

14. Increased creatinine indicates:

A. Good renal function
B. Impaired renal function
C. Liver disease only
D. Hypoglycemia
Answer: B. Impaired renal function

15. Normal male serum creatinine:

A. 0.7–1.3 mg/dL
B. 2–4 mg/dL
C. 5–7 mg/dL
D. 10 mg/dL
Answer: A. 0.7–1.3 mg/dL

16. Normal female serum creatinine:

A. 0.6–1.1 mg/dL
B. 2–3 mg/dL
C. 4–5 mg/dL
D. 6 mg/dL
Answer: A. 0.6–1.1 mg/dL

17. Reagent R1 contains:

A. Picric acid
B. Urea
C. Sulfuric acid
D. Glucose
Answer: A. Picric acid

18. Reagent R2 contains:

A. Sodium hydroxide
B. Sulfanilic acid
C. Phosphate buffer
D. Cholesterol esterase
Answer: A. Sodium hydroxide

19. Blank contains:

A. Sample
B. Standard
C. Distilled water
D. Serum
Answer: C. Distilled water

20. Standard used in calculation:

A. Yes
B. No
C. Only blank
D. Optional
Answer: A. Yes

21. Formula based on:

A. Test / Standard
B. Standard / Test
C. Blank / Test
D. Test / Blank
Answer: A. Test / Standard

22. Sample volume commonly used:

A. 10 µL
B. 100 µL
C. 500 µL
D. 1000 µL
Answer: B. 100 µL

23. Working reagent volume:

A. 1000 µL
B. 100 µL
C. 10 µL
D. 500 µL
Answer: A. 1000 µL

24. Creatinine rises in:

A. Acute kidney injury
B. Chronic kidney disease
C. Dehydration
D. All of the above
Answer: D. All of the above

25. Creatinine decreases in:

A. Pregnancy
B. Muscle wasting
C. Severe liver disease
D. All of the above
Answer: D. All of the above

26. Creatinine helps estimate:

A. GFR
B. Blood sugar
C. Bilirubin
D. Calcium
Answer: A. GFR

27. Creatinine is part of:

A. LFT
B. RFT
C. Lipid profile
D. Thyroid profile
Answer: B. RFT

28. High creatinine seen in urinary:

A. Obstruction
B. Hypoglycemia
C. Anemia
D. Jaundice
Answer: A. Obstruction

29. Creatinine depends on:

A. Muscle mass
B. Diet only
C. Age only
D. Temperature
Answer: A. Muscle mass

30. Creatinine is non-protein:

A. Yes
B. No
C. Protein
D. Lipid
Answer: A. Yes

Short MCQs (31–50)

  1. Creatinine method = Jaffe method
  2. Reaction medium = Alkaline
  3. Main color = Orange-red
  4. Main reagent = Picric acid
  5. Sample type = Serum
  6. Wavelength = 492 nm
  7. Creatinine marker for kidney = Yes
  8. Creatinine filtered by glomerulus = Yes
  9. Reabsorption minimal = Yes
  10. Creatinine rises in renal failure = Yes
  11. Creatinine decreases in pregnancy = Yes
  12. Male normal value = 0.7–1.3 mg/dL
  13. Female normal value = 0.6–1.1 mg/dL
  14. Standard required = Yes
  15. Blank contains water = Yes
  16. Reagent volume = 1000 µL
  17. Sample volume = 100 µL
  18. Creatinine used in GFR = Yes
  19. Creatinine routine biochemical test = Yes
  20. Creatinine important in RFT = Yes
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