Serum C peptide level and renal function in diabetes mellitus

Serum C peptide level and renal function in diabetes mellitus C peptide is an active peptide hormone with potentially important physiological effects. C peptide has the capacity to diminish glomerular hyperfiltration and reduce urinary albumin excretion in both experimental and human type 1 diabetes. The present study is aimed at correlating the serum C peptide level with that of renal clearance, urinary albumin excretion and duration of diabetes. This is a prospective cross sectional study. Patients with diagnosis of type 2 diabetes mellitus were evaluated for their baseline clinical and laboratory profile.

Both males and females above the age of 18 years were included in the study. The laboratory investigations include fasting serum C peptide, HbA 1C , serum creatinine, blood urea nitrogen, urine albumin and creatinine. Creatinine clearance was calculated using modification of diet in renal disease formula from serum creatinine value. A total of 168 patients were included in the study, among them 90 were females (53.57%) and 78 males (46.43%). Mean age of the patients was 57.64 years. Pearson correlation test showed negative correlation of serum C peptide level with creatinine clearance, though statistically not significant.

Negative correlation was also seen between serum C peptide, and urine albumin, urine albumin creatinine ratio, HbA 1C and duration of diabetes. Mean urine albumin was higher in patients with subnormal C peptide level. Duration of disease was more in patients with lower serum C peptide level.

The study has shown weak association of serum C peptide level with microalbuminuria and creatinine clearance. Risk of albuminuria is more in patients with low serum C peptide level. In insulin bio-synthesis, C-peptide is cleaved from pro-insulin, stored in secretory granules, and eventually released into the bloodstream in amounts equimolar with those of insulin. C-peptide has an essential function in the synthesis of insulin in that it links the A and B chains in a manner that allows correct folding and inter-chain disulfide bond formation. [1]

The kidney has been suggested as the main organ for the degradation of C-peptide. Half-life of C peptide in circulation is 2-5 times longer than insulin. [2] C peptide is the more reliable indicator of insulin secretion than insulin itself. Furthermore, the concentration of C peptide is not affected by interference from insulin antibodies often present in patients receiving insulin therapy After the discovery of the mode of insulin biosynthesis, several early studies addressed the question of possible physiological effects of C-peptide.

Insulin-like effects on blood glucose levels and glucose disposal after glucose loading were looked for but not found. [7],[8] Recently, new data have been presented demonstrating specific binding of C-peptide to cell surfaces in a manner that suggests the presence of G protein-coupled membrane receptors. C-peptide may thereby stimulate specific intracellular processes, influencing renal and nerve function in C-peptide-deficient type 1 diabetes patients. [3]

The study has shown weak association of serum peptide level with microalbuminuria and creatinine clearance. Patients with low serum C peptide level may have increased risk of microalbuminuria. C-peptide replacement together with insulin administration may be beneficial in type 1 diabetes patients. Studies involving C-peptide administration of longer duration will be required to determine whether C-peptide may have a role in the prevention and treatment of diabetic nephropathy.

Markeri metabolici

Scop: Identificarea copiilor cu risc de a dezvolta diabet zaharat insulinodependent (DZ tip 1).

Material si metode: Lotul studiat include 41 de copii (virsta intre 3 luni si 18 ani) repartizati in 4 grupe de studiu: 32 de copii (fratii copiilor cu DZ tip 1) au fost inclusi in grupul A, 5 copii investigati pentru alterarea glicemiei a jeun au format grupul B, 1 sugar in virsta de 3 luni provenit din mama diabetica a reprezentat grupul C, 3 cazuri cu DZ tip 1 la debut investigati inainte de instituirea terapiei insulinice au reprezentat grupul D. La toate cazurile s-a determinat: glicemia a jeun, hemoglobina glicozilata (HbA1c), colesterolul, trigliceridele, HDLc. in acelasi timp s-au determinat markerii autoimunitatii umorale prin determinarea titrului anticorpilor anti decarboxilaza acidului glutamic (antiGAD), anticorpii anti insule pancreatice (anti ICA). in grupurile A, B si C s-au considerat pozitive titrele pentru percentila 97 si in grupul D pentru percentila 95. Dintre markerii metabolici am determinat concentratia peptidului C, cu valori normale intre 0,5-3 ng/ml.

Rezultate: in lotul A: 3 copii (9,37%) au fost GAD (+) si ICA (+), 23 cazuri (71,87%) au fost GAD (+) si ICA (-), iar 6 cazuri (18,75%) au fost GAD (-) si ICA (-). Peptidul C a fost in limite normale la cele 6 cazuri GAD (-) si ICA (-), si cu valoare mai mica de 0,5 ng/ml la cele 3 cazuri GAD (+) si ICA (+). La cele 23 cazuri GAD (+) si ICA (-) valorile peptidului C au fost atit in limite normale, cit si in afara intervalului normal. HbA1c a fost in limite normale la toate cazurile. in lotul B toate cele 5 cazuri au fost GAD (+) si ICA (-), iar HbA1c a fost normala. Sugarul provenit din mama diabetica (lot C) a fost GAD (-) si ICA(-) cu o valoare HbA1c = 5,3% si peptid C = 2,077 ng/ml. Lotul D (3 copii la debutul DZ tip 1) au fost GAD (+) si ICA (-). Peptidul C a fost in limite normale la 2 cazuri, iar al treilea a prezentat scaderea secretiei de peptid C (0,191 ng/ml). HbA1c a depasit valoarea de 12% la toate cele 3 cazuri.

Concluzii: Anticorpii anti GAD par sa aiba legatura cu debutul DZ tip 1. Scaderea peptidului C pare sa se coreleze numai cu prezenta concomitenta a anticorpilor anti GAD, cit si a ICA.

Interpreting Your C-peptide Values

Thomas Connors
Sep 1, 2000

Normal C-peptide levels for a fasting test are generally considered to be anything between 0.5 nanograms (ng) per millileter (ml) and 3 ng/ml, although people who do not have diabetes may occasionally stray out of this range. The following is a range of C-peptide values in people without diabetes, as compiled by Endocrine Sciences, Inc., a California-based laboratory that conducts the test. It should be noted that, in some cases, subjects fell below the normal range of C-peptide values, but were still not found to have diabetes. The range of values may also vary according to what lab your health care practitioner uses.

Children (< 15 years old) 8:00 a.m. fasting: 0.4 to 2.2 ng/ml

Adults 8:00 a.m. fasting: 0.4 to 2.1 ng/ml

Two hours postprandial (after a meal): 1.2 to 3.4 ng/ml

Two hours post glucose load: 2.0 to 4.5 ng/ml

Although anything less than these numbers is generally an indicator of type 1 diabetes, values within the normal range can mean different things.

Type 2s with insulin resistance could actually be making more insulin than a non-diabetic slim person,” says Richard Bernstein, MD, FACE, FACN, CWS, of the Diabetes Center in Mamaroneck, New York. Values on the lower end may also indicate a honeymoon phase of type 1, when insulin production is slowing down but has not yet ground to a halt.

Bernstein also points out that even in type 1s, a positive C-peptide test should be a source of optimism.

“Of all my patients, I only have two who don’t make any C-peptide, and I’m one of them,” Bernstein says. He says this proves that most type 1s still produce at least some insulin and raises the possibility that therapies like beta-cell regeneration may eventually restore normal BG levels.