Cystatin C

Cystatin C is a protein of the cysteine protease inhibitor group that is mostly produced in nucleated cells. Its production is not affected by inflammatory or consumptive diseases.

Cystatin C is exclusively glomerular filtered and reabsorbed by the proximal tubule epithelium. Thus, the value describes the performance of glomerular filtration of the kidney. It shows a stable production rate. In contrast, creatinine is glomerularly filtered and additionally tubularly secreted (creatinine-blind region; see also below under “Further notes”).

Cystatin C has several advantages over creatinine determination because it is less influenced by various factors such as muscle mass, gender, or diet.

The determination of cystatin C clearance can be determined using the following formula:

  • Glomerular filtration rate (ml(min) = 74.835/cystatin C (mg/l)1.333 – see below kidneycalculator.com.

The procedure

Material needed

  • Blood serum

Preparation of the patient

  • Blood collection must be performed in the morning fasting

Interfering factors

  • Higher values (up to 10%) can be measured when standing/sitting upright than when lying down.
  • Diseases that may lead to an increase in serum cystatin C levels: Obesity (adiposity), diabetes mellitus, malnutrition, and inflammation.
  • There is a strong dependence on thyroid function, so cystatin C should not be used even in the presence of latent hyper-/hypothyroidism (hyperthyroidism and hypothyroidism):
  • Medications: high-dose corticosteroid therapy → increase in serum cystatin C level.

Normal values in children

Age Standard values in mg/l
Newborn 1,37-1,89
1-12 months 0,73-1,17
1 to < 3 years 0,68-1,60
3 to < 16 years 0,51-1,31

Normal values in adults

Gender Normal values in mg/l
Female 0,57-0,96
Male 0,50-0,96

Indications

As well as for therapy control of the above diseases.

Interpretation

Interpretation of elevated values

  • Impaired glomerular filtration rate

Interpretation of decreased values

  • Not relevant to the disease

Further notes

  • Cystatin C shows greater sensitivity (percentage of diseased patients in whom the disease is detected by the use of the test, i.e., a positive test result occurs) and specificity (probability that actually healthy people who do not have the disease in question are also detected as healthy in the test) than creatinine in serum (more light in the “creatinine blind region”) in the range between 80-40 ml/min (GFR).
  • Cystatin C is further more suitable than creatinine determination for the detection and risk classification of chronic kidney disease.