Diabetologia 9 Springer-Verlag 1989

Transcription

1 Diabetlgia (1989) 32: Diabetlgia 9 Springer-Verlag 1989 Fasting plasma C-peptide, glucagn stimulated plasma C-peptide, and urinary C-peptide in relatin t clinical type f diabetes H. J. Gjessing 1, L. E. Matzen 1, O. K. Faber a and A. Frland 1 1 Medical Department, Fredericia Hspital, and 2 Medical Department, Hrshlm Hspital, Denmark Summary. Many patients with Type 2 (nn-insulin-dependent) diabetes mellitus are treated with insulin in rder t cntrl hyperglycaemia. We studied fasting plasma C-peptide, glucagn stimulated plasma C-peptide, and 24 h urinary C- peptide in relatin t clinical type f diabetes in 132 insulin treated diabetic subjects. Patients were classified clinically as Type 1 (insulin-dependent) diabetic subjects in the presence f at least tw f the fllwing criteria: 1) significant ketnuria, 2)insulin treatment started within ne year after diagnsis, 3) age f diagnsis < 40 years, and 4) weight belw 110% f ideal weight f the same age and sex. Eighty patients were classified as Type 1 and 52 as Type 2 diabetic subjects. A secnd classificatin f patients int 6 C-peptide classes was then perfrmed. Class I cnsisted f patients withut islet B- cell functin. Class II-VI had preserved islet B-cell functin and were separated accrding t the 20%, 40%, 60% and 80% C-peptide percentiles. The tw classificatins f patients were cmpared by calculating the prevalence f clinical Type I and Type 2 diabetes in each f the C-peptide classes. This analysis shwed that patients with a fasting plasma C-peptide value < 0.20 nml/1, a glucagn stimulated plasma C-peptide value < 0.32 nml/1, and a urinary C-peptide value < 3.1 nml/1, r < 0.54 nml/mml creatinine/24 h, r < 5.4 nml/24 h mainly were Type I diabetic patients; while patients with C- peptide levels abve these values mainly were Type 2. At these limits the percentage, predictive value f psitive tests as indicatrs f Type 2 diabetes were as fllws: fasting C-peptide 83%, stimulated C-peptide 86%, and urinary C-peptide expressed as nml/1 76%, as nml/mml creatinine/24 h 79%, and as nml/24 h 78%. Similarly, the percentage predictive value f negative tests as indicatrs f Type 1 diabetes were as fllws: fasting C-peptide 86%, stimulated C-peptide 88%, and urinary C-peptide expressed as nml/1 79%, as nml. mml creatinine-24 h 81%, and as nml/24 h 80%. If patients withut detectable C-peptide were excluded, the predictive value f negative tests were as fllws: fasting C-peptide 81%, stimulated C-peptide 88%, urinary C-peptide expressed as nml/161%, as nml/mml creatinine/24h 69%, and as nml/24 h 64%. In cnclusin, pst glucagn C-peptide gives a gd distinctin between Type 1 and Type 2 diabetes mellitus in insulin treated diabetes while 24 h urinary C-peptide gives a less sensitive distinctin between the clinical types f diabetes. Key wrds: Type ~ t,,~u,.-ucpcadent) diabetes mellitus, Type 2 (nn-insulin-dependent) diabetes mellitus, islet B-cell functin, plasma C-peptide, urinary C-peptide. Classificatin f diabetes int Type I (insulin-dependent) and Type 2 (nn-insulin-dependent) diabetes mellitus is clinical [1]. Patients with Type I diabetes are ketsis-prne and require insulin t sustain life due t a severe defect in islet B-cell functin, while patients with Type 2 diabetes are nn-ketsis-prne, ften bese, and have defects in bth insulin actin and secretin. Furthermre, Type 2 diabetes is nly rarely diagnsed befre the age f 40 years [2]. The clinical classificatin f patients int Type I and Type 2 diabetes is suppsed t reflect differences in islet B-cell functin between the tw types f diabetes. We, therefre, fund it f interest t study estimates f islet B-cell functin in patients with clinical Type I and Type 2 diabetes mellitus. The C-peptide respnse t glucagn was intrduced fr mre than a decade ag as a measure f pancreatic respnsiveness in Type i diabetes mellitus [3]. The test has nw becme widely used in patients with Type 1 diabetes [4-9] but als in patients with Type 2 diabetes mellitus [8-11]. The test has als been used in attempts t discriminate between Type 2 diabetic patients with and withut insulin requirement in rder t cntrl hyperglycaemia [8, 9]. Hwever, nly Hekstra et al. have evaluated the test in discriminatin between Type 1 and Type 2 diabetes [12]. They discntinued insulin therapy in 11 bese insulin treated diabetic subjects. The tw C-peptide nn-respnders had t resume insulin due t a large increase in ketne bdy levels

2 306 H. J. Gjessing et al.: C-peptide and clinical type f diabetes ~tm t I ~ i c~ ~ T 9 =~ 0%- ~-.5- ~ iv ~ , ~020- ~--- ~-- ~ '~ 8 Jl '-' I ll "+k _L 9 m 0%,0 [ - - I I Type 1 Type 2 Type 1 Type 2 ~2.,5 <u tm 6~-- zx 7-_ I I ~ F--1 Type 1 Type t:l ~ 16.0 t._~ :~ 0.B ~ i = ~ ca_~ m 28 v1 % Ivi I _l v = ar'i ~ -- Y ~, ~ d, "C 0.6 t f r - - i Type 1 Type 2 Type 1 Type 2 I Fig.l. Fasting plasma C-peptide, glucagn stimulated plasma C-peptide, and the mean f three 24 h urinary C-peptide values expressed as nml/1, nml/mml creatinine/24 h, r nml/24 h in relatin t clinical type f diabetes in insulin treated diabetic subjects marked accrding t dm'atin f diabetes. Patients were divided int six C-peptide classes. Class I and II were separated accrding t the "effective" detectin limit f C-peptide in plasma r urine. Class II-VI were separated accrding t the 20%, 40%, 60%, and 80% C-peptide percentiles fr patients with C-peptide values abve "effective" detectin limit. Figures n the rdinate indicate the limits between the six C- peptide classes. 9 Type I (insulin-dependent) diabetic subjects with diabetes duratin _< 2 years 9 Type 1 diabetic subjects with diabetes duratin > 2 years A Type 2 (nn-insulin-dependent) diabetic subjects with diabetes duratin < 2 years 9 Type 2 diabetic subjects with diabetes duratin > 2 years while n ketacidsis develped in the 9 C-peptide respnders. The authrs cncluded, that measuring C- peptide after glucagn is a simple test that may be a discriminative methd t establish insulin dependency in bese diabetic patients treated with insulin. Many patients with Type 2 diabetes mellitus are treated with insulin in rder t cntrl hyperglycaemia [2]. We, therefre, expected insulin treated diabetic subjects fllwed at the utpatient clinic, medical department, Fredericia Hspital Fredericia, Denmark, t be a mixture f patients with Type 1 and Type 2 diabetes mellitus. Amng 132 patients f this ppulatin, fasting plasma C-peptide, glucagn stimulated plasma C-peptide, and 24 h urinary C-peptide were related t the clinical type f diabetes. Subjects Patients and methds Fredericia Hspital serves a ppulatin f apprximately 50,000. Frm a study f prescriptins, it appeared that apprximately 80% f insulin treated diabetic subjects in the area are fllwed at the clinic. All 178 insulin treated diabetic subjects aged 18 years r mre, with a duratin f diabetes fr mre than six mnths and attending the clinic were invited t participate in the study. Thirty-five patients were nt interested. Eleven patients with a plasma creatinine abve 150 ~tml/t were excluded; 132 patients entered the study. Nine patients were nt able t cllect the 24 h urinary samples. Each patient was classified accrding t clinical type. Type 1 diabetes was cnsidered in the presence f at least tw f the fllwing criteria: 1. significant ketnuria (mre than + at ketstix crrespnding t a urinary acetacetate cncentratin abve 4 retl/l) at diagnsis r any time after diagnsis, 2. insulin treatment initiated within ne year after diagnsis, 3. age at diagnsis < 40 years, and 4. weight < 110% f the ideal weight fr the same sex and age (13). Type 2 diabetes was cnsidered in the abscence f such criteria r in the presence f nly ne criterin. Using these criteria, 80 patients were cnsidered Type 1 while 52 were cnsidered Type 2 diabetic subjects. A secnd classificatin f patients int 6 C-peptide classes was then perfrmed. Class 1 cnsisted f patients withut detectable C-peptide in plasma (< 0.06 nml/1) r urinary C-peptide values < 0.3 nml/1, < 0.06 nml/mml creatinine/24 h, r < 0.6 nml/24 h. These urinary C-peptide values ("effective" detectin limits) crrespnd t a plasma C-peptide cncentratin < 0.06 nml/1 [14]. Classes II-VI cnsisted f patients with increasing C-peptide levels abve the "effective" detectin limit separated accrding t the 20%, 40%, 60% and 80% percentiles. The tw different classificatins culd then be matched by calculating the prevalence f Type 1 and Type 2 diabetes in each f the C- peptide classes. Furthermre, predictive values (see methds sectin) f psitive tests as indicatrs f Type 2 diabetes and f negative tests as indicatrs f Type 1 diabetes culd be calculated at the C-peptide limits separating the 6 C-peptide classes. All patients were treated with intermediately acting insulin alne r in cmbinatin with regular insulin given nce r twice daily. The

3 H. J. Gjessing et al.: C-peptide and clinical type f diabetes % i,, I II Ill IV V Vl Class I II Ill IV V Vl % % Fasting piasma I~176 C-pepfide (nmtlt) E-pepfide (nm[it) Sfimulafed plasma, ] 0 Crass II Ill IV V Vl I I I I I I ,52 Fasfing plasma C-pepfide (nm[i[ I II Ill IV V Vl I I' I I I I I,06, Sfimutafed plasma C-pepfide (nm[ii) 307 1~176 I, I t, Urinary C-pepfide (nml/t) / ,, j,, I00 50 l.6.33.s~ _J Urinary C-peptide (nm[imml. creqtininel21, h) IO0 f ~ Urinary C-peptide (nm[12/* h) Esfimafed insulin secrefin 0 rare (UI2/* h) Fig.2. Prevalence f Type 1 ra and Type 2 [] (tiabetes in C-peptide classes last insulin injectin was given either in the mrning r late in the afternn n the day preceeding the investigatin. Patients were studied after an vernight h fast. [ 'I I l I I I I I I I I I I t ,5k Urinary C-peptide Urinary C-peptide (nm[/i) (nmt/mm[ cretinine/2/,h) I I I l I I I B 5A Urinary C-pepfide (nm0t/2/, h) Fig.3. Predictive values f psitive tests in the detectin f Type 2 diabetes (( ) and f negative tests in the detectin f Type 1 diabetes ( H ) at the limits separating C-peptide class I-VI. Predictive values f negative tests are als shwn when patients belnging t class I are excluded (z~ Zx) Me~~ Plasma C-peptide was measured befre and 6 min after intravenus injectin f I mg f glucagn. The same mrning the patients cmpleted the third cnsecutive 24-h urinary cllectin. Twenty-fur h urinary samples were cllected at hme in plastic cntainers. Patients were instructed t keep the samples under refrigeratin during the cllectin perid. After vlume measurement an aliqut f the urine was adjusted t ph with 5 mml/1 NaOH and kept frzen at - 20 ~ C until assay. After thawing, the urinary samples were diluted with a 0.04 ml/1 phsphate buffer cntaining 0.1% albumin and NaC1 t make the buffer istnic. Measurement f urinary C-peptide was perfrmed in the cncentratin range nml/1. Immunreactivity f C-peptide in the urine and plasma was determined by the methd f Heding [5] using antibdy M1230 [16]. The intra- and interassay cefficients f variatin f the C-peptide assay is 3.2% and 9.2%, respectively. The detectin limit f C-peptide in plasma is 0.06 nml/1 as determined frm measurement f C-peptide in plasma frm pancreatectmised patients [17]. Detectin limit f C-peptide in urine is 0.1 nml/l defined as the lwest cncentratin which with 95% cnfidence limits can be distinguished frm zer. Twenty-fur h urinary C-peptide values f 0.3 nml/1, 0.06 nml/mml creatinine/24 h, r 0.6 nml/24 h crrespnd t a plasma C-peptide value f 0.06 nml/1, s-called "effective" detectin limits [14]. The 24 h urinary C-peptide excretin was calculated as the mean value f the three samples and expressed as nml/l, nml/uml urinary creatinine/24 h, and nml/24 h. Adjustment with urinary creatinine may crrect fr differences in bdy size [18] and glmerular filtratin rate [19]. Peripheral plasma free insulin cncentratins were measured accrding t Heding [20]. Fasting bld glucse was measured by a hexkinase methd [21]. Infrmed cnsent was btained in all patients. The study was apprved by The Ethical Cmmittee f Funen and Vejle Cunties. Statistical analysis Kruskall-Wallis' nn-parametric ranked-sum test was used in cmparing median values in C-peptide grups. The level f significance was set at 2c~ = Figures fr predictive values f psitive and negative tests were calculated as fllws: Predictive value f psitive test (%)= (number f patients classified as Type 2 diabetic subjects with a C-peptide value abve the specified limit/ttal number f patients with a C-peptide value abve the specified limit) 100. Predictive v~ilue<f negative test (%) = (number f patients classified as Type 1 diabetic subjects with a C-peptide value belw the spedried limit/ttal number f patients with a C-peptide value belw the specified limit) 100.

4 308 H.J. Gjessing et al.: C-peptide and clinical type f diabetes Table 1. Predictive value f psitive test in the detectin f Type 2 (nn-insulin-dependent) diabetes and f negative test in the detectin f Type 1 was (insulin-dependent) diabetes at the plasma and urinary C-peptide levels separating class III and IV in Figures 1 and 2 (95% cnfidence limits). Values are given in patients with diabetes duratin > 1/2 year and in patients with diabetes duratin > 2 years Diabetes C-peptide Predictive value Predictive value Predictive value duratin limit f psitive test f negative test f negative test when excluding patients f class I >1/2 year F-CP 0.20 nml/l 83% (70-93%) 86% (76-92%) 81% (63-93%) S-CP 0.32 nml/1 86% (73-94%) 88% (79 94%) 88% (71-96%) UCP 3.1 nml/1 76% (60-88%) 79% (69-87%) 61% (41-79%) UCP 0.54 nml/mml/24 h 79% (63-90%) 81% (71-89%) 69% (49-85%) UCP 5.4 nml/24h 78% (62 89%) 80% (70-88%) 64% (44-81%) F-CP _> 0.20 nml/1 + 87% (74-95%) - S-CP > 0.32 nml/l F-CP < 0.20 nml/l+ - 88% (78-94%) S-CP < 0.32 nml/1 UCP _> 0.54 nml/mml/24 h+ 86% (71-95%) S-CP > 0.32 nml/1 UCP < 0.54 nml/mml/24 h % (78-94%) S-CP < 0.32 nml/l >2 years F-CP 0.20 nml/1 97% (86-100%) 86% (76-93%) 79% (58-93%) S-CP0.32nml/1 95% (83-99%) 88% (78-94%) 87% (66-97%) UCP3.1 nml/1 90% (74-98%) 79% (68-88%) 57% (34-77%) UCP 0.54 nml/mml/24 h 97% (83-100%) 82% (71-90%) 68% (47-85%) UCP 5.4 nml/24 h 94% (79-99%) 82% (71-90%) 64% (41-83%) F-CP = fasting plasma C-peptide, S-CP = glucagn stimulated plasma C-peptide, UCP = mean f three 24 h urinary C-peptide values Results Figure 1 shws the fasting, stimulated, and urinary C- peptide values in patients cnsidered Type i and Type 2 diabetic subjects marked whether diabetes duratin was abve r belw 2 years. A large verlap was fund in C-peptide values between patients with Type 1 and Type 2 diabetes. Six patients were classified as Type 2 diabetic subjects but had plasma C-peptide levels belw 0.06 nml/1 tgether with urinary C-peptide values belw the crrespnding "effective" detectin limits. Figure 2 shws the prevalence f Type 1 and Type 2 diabetes in the 6 C-peptide classes. The majrity f patients in class I-III were classified as Type 1 while the majrity f patients in class IV-VI were classified as Type 2 diabetic subjects. In Fig. 3 are shwn predictive values f psitive and negative tests at the limits between the 6 C-peptide classes. The best discriminatin between Type 1 and Type 2 diabetes was btained at the limit between class III and IV. In Table I predictive values are shwn with 95% cnfidence limits f negative and psitive tests at the limits separating class III and IV. C-peptide after glucagn tended t give the best discriminatin between the clinical types f diabetes while urinary C-peptide tended t give a less distinct discriminatin. The prevalence f Type I diabetes was high in class I whether using C-peptide determinatin in plasma r in urine. Figure 3 als shws the predictive values f negative tests at the limits between class II-VI when patients belnging t class I are excluded. The predictive value f a negative test at the limit between class III and IV was nw significantly higher (p < 0.05) using C-peptide determinatin pst glucagn than using urinary C-peptide as islet B-cell estimate cnsidering the 95% cnfidence limits f the predictive values (Table 1). Table 1 als shws that the predictive values f stimulated plasma C-peptide cncentratins abve r belw the limit between class III and IV wuld nt increase if they were cmbined with fasting plasma C-peptide cncentratins r with urinary C-peptide values abve r belw the crrespnding limit between class III and IV. Table 1 finally shws that the predictive values f psitive tests using all estimates f islet B-cell functin wuld increase t 90-97%, if nly patients with a duratin f diabetes > 2 years were included in the study. In this case, the predictive values f negative tests were, hwever, almst unchanged. Patients belnging t class II+III and t class V+ VI had preserved B-cell functin and were each hmgenus in the respect that the prevalence f Type 1 diabetes was very high in class II + III and the prevalence f Type 2 diabetes very high in class V+ VI when using stimulated C-peptide as islet B-cell estimate. Table 2 shws the average number f Type 1 clinical features in the tw types f diabetes in the stimulated C-peptide classes, when cmbining patients f class II +III and f class V+ VI. There was n significant assciatin between number f clinical features and C-peptide levels when analysing patients with Type 1 and Type 2 diabetes separately. Table 3 shws,different clinical characteristics f the patients als when cmbining the stimulated C-peptide class II +III and V+V1. Patients belnging t class IV and class V+VI were the ldest. Sex distributin was

5 H.J. Gjessing et al.: C-peptide and clinical type f diabetes Table 2. Mean number f features f Type 1 diabetes (ketnufia, early insulin treatment, age f diagnsis _< 40 years, and nrmal weight) in stimulated C-peptide classes in patients classified as Type 1 r Type 2 diabetic subjects Type f diabetes Class I Class II+III Class IV Class V+VI ~pel n=45 n=28 n=4 n=3 ~pe n=6 n=4 n=12 n=30 Class I: Glucagn stimulated plasma C-peptide <0.06 nml/l. Class II+III: Glucagn stimulated plasma C-peptide < 0.32 nml/l. Class IV: Glucagn stimulated plasma C-peptide < 0.60 nml/1. Class V+ VI: Glucagn stimulated plasma C-peptide > 0.60 nml/1. n = number f patients studied similar in the grups. Duratin f diabetes was lngest in patients belnging t class I. Bdy mass index was highest in patients belnging t class II +III. Insulin dse was inversely assciated with C-peptide. Plasma peripheral insulin levels were highest in patients belnging t class V+VI. Fasting bld glucse was highest in patients withut islet B-cell functin. The influence f duratin f diabetes n median stimulated C-peptide in class II +III, class IV, and class V+VI is shwn in Table 4. In patients f class II +III, an bvius decline in median C-peptide value was fund when the duratin f diabetes was > 5 years as cmpared t < 5 years (p < 0.01). In the ther classes, n significant assciatin was fund between stimulated C-peptide and the duratin f diabetes. Discussin Our study ppulatin cnsisted f a sample f insulin treated diabetic utpatients in whm insulin treatment was given withut any rigid r reprtable criteria. Many patients with Type 2 diabetes are treated with insulin in rder t cntrl hyperglycaemia [2], and we, therefre, expected a certain part f the patients t have Type 2 diabetes. Hwever, n criteria exist that permit a mutually exclusive discriminatin between Type 1 and Type 2 diabetes. Even fr the same subject classificatin can change with the cnditin f the patient [22]. Any classificatin f patients int Type I and Type 2 diabetic subjects must be based n arbitrary criteria. In ther studies, early insulin treatment and significant ketnuria have been used as criteria f Type 1 diabetes, while the lack f these criteria have been used t diagnse Type 2 diabetes [2]. In ur study, we fllwed the clinical differences utlined by WHO [1]. Thus, the criteria fr Type 1 diabetes were ketnuria at diagnsis r later, early insulin treatment, diagnsis befre 40 years and nrmal weight. In rder t reduce the Table 3. Median value and range f sme clinical characteristics f 132 insulin treated diabetic subjects, when dividing the patients int different classes accrding t glucagn stimulated C-peptide levels Variable Class I Class II Class IV Class V+ VI n=51 n=32 n=16 n=33 Sex (F/M) 35/16 16/16 11/5 20/13 NS Age a (years) (19-83) (18-76) (21-77) (38-87) Duratin f diabetes mellitus a (years) (3-51) (1-25) (2-26) (1-43) Bdy mass index b (kg/m 2) ( ) ( ) ( ) ( ) Insulin dse a (U/kg) ( ) ( ) ( ) ( ) Plasma free b insulin (pml/1) (0-272) (10-276) (0-99) (17-580) Bld glucse b (mml/1) ( ) ( ) ( ) ( ) Class I: Stimulated C-peptide. < 0.06 nml/1. Class II +III: Stimulated C-peptide < 0.32 nml/1. Class IV: Stimulated C-peptide < 0.60 nml/1. Class V+ VI: Stimulated C-peptide >_ 0.60 nml/1. n = number f patients studied a = p < 0.01, b = p < 0.001, NS = nt significant Table 4. Median and range f glucagn stimulated plasma C-peptide values in C-peptide classes, gruped by duratin f diabetes Median plasma C-peptide (nml/1) Duratin f diabetes < 5 years 5- < 10 years > 10 years Class II +III a n=11 n=12 n~9 Class IV NS n=3 n=6 n=7 Class V+VI NS n=9 n=12 n=12 Class II +III: Glucagn stimulated plasma C-peptide < 0.32 nml/l. Class IV: Glucagn stimulated plasma C-peptide < 0.60 nml/l. Class V+VI: Glucagn stimulated plasma C-peptide >0.60 nml/l. n = number f patients studied a= p < 0.01 number f "false psitive" Type I diabetic subjects, at least tw f the criteria shuld be present t allw the diagnsis Type I diabetes. Type 2 diabetes was cnsidered in the abscence f any criterin, r if nly ne criterin was present. Measurement f islet cell autantibdies r HLA-typing were nt perfrmed. The predictive value f a stimulated plasma C-peptide cncentratin abve and belw 0.32 nml/1 as indicatr f Type 2 and Type I diabetes was as high as 86% and 88%, respectively. The predictive values f psitive tests culd be further increased at higher stimu- 309

6 310 lated plasma C-peptide levels. Thus, the predictive value f a stimulated C-peptide level abve and belw 0.60 nml/1 as indicatr f Type 2 and Type 1 diabetes was 91% and 78%, respectively. A plasma C-peptide level f 0.60 nml/1 has previusly been suggested t discriminate between Type 2 diabetic subjects with and withut insulin requirement [8, 9]. In ur study, apprximately 75% f patients with a stimulated plasma C-peptide cncentratin frm 0.32 nml/1 t 0.60 nml/1 were clinically Type 2 diabetic subjects. In anther study, we discntinued insulin treatment in 25 patients with a stimulated value abve 0.33 nml/l [22]. After 3 mnths, nly 4 patients had t resume insulin treatment due t hyperglycaemia. Ketnuria develped in nne f the patients. The predictive values f fasting C-peptide abve r belw 0.20 nml/1 were almst as high as thse btained using stimulated C-peptide abve r belw 0.32 nml/1. Basal C-peptide and stimulated C-peptide, therefre, seem t give an almst similar infrmatin when used t distinguish between Type 1 and Type 2 diabetes. This agrees with ur previus reprt f a very clse crrelatin between fasting and glucagn stimulated plasma C-peptide in the same patients [23]. Welbrn et al. als related basal C-peptide t clinical types f diabetes and fund a basal C-peptide range frm nml/1 verlapping between Type1 and Type 2 diabetes [24] crrespnding t ur value f 0.20 nml/1. Apprximately 10% (n--6) f ur patients with plasma C-peptide < 0.06 nml/1 were classified clinically as Type 2 diabetic subjects. These 6 patients had as few Type 1 clinical features as Type 2 diabetic subjects with higher C-peptide values (Table 3). In ther studies, it has been suggested that undetectable C-peptide in plasma can be used as indicatr f Type 1 diabetes [2]. Our findings reveal that classificatin based n clinical characteristics makes it difficult t differentiate between patients with Type 2 and slwly prgressing Type 1 diabetes. The prevalence f patients diagnsed as Type2 diabetic subjects in the pst glucagn C-peptide range < 0.32 nml/1 was als apprximately 10%. It seems pssible that these patients als were Type 1 diabetic subjects. Our data, therefre, suggest that a plasma C-peptide value pst glucagn belw 0.32 nml/1 might be used as a criterin f Type I diabetes in future studies. The finding that patients with a stimulated plasma C-peptide range frm 0.06 t < 0.32 nml/1 shwed a prgressive decline in stimulated C-peptide values alng with duratin f diabetes while this was nt the case in patients with higher C-peptide values seems t supprt such a classificatin f patients. Plasma C-peptide pst glucagn shwed a significantly better distinctin between Type 1 and Type 2 diabetes than urinary C-peptide if patients withut B- cell functin were excluded frm the study. Similarly, Kskinen et al. reprted that urinary C-peptide was less H. J. Gjessing et al.: C-peptide and clinical type f diabetes sensitive than pst glucagn C-peptide in the discriminatin between Type 2 diabetic subjects with and withut insulin requirement [9]. The mst imprtant reasn prbably is a large variability f urinary C-peptide excretin [14]. This large variability is prbably mainly due t the fact that nly apprximately 4% f secreted C-peptide fi'm the pancreas is excreted in the urine [25]. Thus, a small change in the renal handling f C- peptide may result in a large change f the amunt f C- peptide excreted in the urine [26]. Other factrs f imprtance culd be different bld glucse and plasma insulin levels during the urinary sampling with subsequent different amunts f stimulatin [11, 27, 28] and inhibitin f the islet B-cells [29, 30]. Similarly, standardisatin f the pre-stimulatry bld glucse cncentratin might have increased the predictive values f C-peptide in plasma as indicatrs f Type 1 and Type 2 diabetes. Including mre C-peptide data in each patient did nt influence the discriminatin f patients. Thus, the distinctin between Type i and Type 2 diabetes was unchanged if stimulated plasma C-peptide was cmbined with fasting plasma C-peptide r urinary C-peptide. Agner el: al. reprted in a prspective study f basal plasma C-peptide during the first 3 years f Type 1 diabetes that ttal remissin wuld last maximally 18 mnths after diagnsis [31]. After 2 years, median basal C-peptide levels were a little lwer than at diagnsis. In ur study, we therefre re-analysed data excluding patients with a duratin f diabetes belw 2 years since these patients might be in the s-called hneymn phase. This prcedure resulted in a better distinctin between Type 1 and Type 2 diabetes since the predictive values f psitive tests increased while the predictive values f negative tests were unchanged. It wuld be f interest t evaluate ur predictive values in a prspective study f Type I and Type 2 diabetic subjects. In the study by Agner et al., less than 25% f newly diagnsed Type 1 diabetic subjects wuld reach fasting C-peptide levels abve 0.30 nml/l during the hneymn phase [31]. The urinary C-peptide excretin rate f 5.4 nml/24 h gave the best discriminatin between Type 1 and Type 2 diabetes. This value crrespnds t an insulin secretin rate f 19 U/24 h (Fig.2) using the infrmatin that apprximately 4% f C-peptide secreted frm the pancreas appears in the urine [25]. The excretin rate f 19 U/24 h is just belw the range frm U/24 h reprted in nrmal subjects [25]. Similarly, the fasting plasma C-peptide value f 0.20 nml/1 is in the lwest range frm 0.15-l.43 nml/1 reprted in 928 nn-diabetic subjects [28]. In mst diabetic subjects, the diagnsis f Type 1 r Type 2 diabetes is nt difficult frm clinical data f the patients [321. Hwever, we believe that measurement f basal C-peptide r C-peptide pst glucagn may be f value in the chice f treatment fr example in patients in whm insulin withdrawal is cnsidered due t a de-

7 H. J. Gjessing et al.: C-peptide and clinical type f diabetes creasing need f exgenus insulin. Furthermre, measurement f C-peptide might be f value in dysregulated perhaps bese subjects n maximal dses f ral antidiabetic agents in whm insulin may be the crrect chice f therapy. We cnclude that plasma C-peptide after glucagn stimulatin and basal C-peptide give a gd discriminatin between clinical Type I and Type 2 diabetes, while 24 h urinary C-peptide seems t be less sensitive in this discriminatin. Acknwledgements. The study was supprted by Vejle Cunty Research Fundatin. Glucagn was supplied by NOVO A/S. Plasma and urinary C-peptide, as well as plasma free insulin measurement were perfrmed at Hagedrn Research Labratry, Gentfte, Denmark. References 1. Wrld Health Organizatin (1985) Diabetes Mellitus. Technical Reprt Series 727. Geneva, Switzerland 2. Laaks M, Py6ral~i K (1985) Age f nset and type f diabetes. Diabetes Care 8: Faber OK, Binder C (1977) C-peptide respnse t glucagn. A test fr the residual B-cell functin in diabetes mellitus. Diabetes 26: Sj6berg S, Gunnarssn R, Ostman J (1983) Residual C-peptide prductin in type 1 diabetes mellitus. Acta Med Scand 214: Siegler DE, Reeves ML, Skyler JS (1982) Lack f effect f imprved glycemic cntrl n C-peptide secretin in patients withut residual B-cell functin. Diabetes Care 5: Gnen B, Gldman J, Baldwin D, Gldberg RB, Ryan WG, Blix PM, Schantzlin D, lilts KH, Rubenstein AH (1979) Metablic cntrl in diabetic patients. Effect f insulin secretry reserve (measured by plasma C-peptide levels) and circulating insulin antibdies. Diabetes 28: Stiller CR, Dupre J, Gent M, Jenner MR, Kewn PA, Laupacis A, Martell R, Rdger NW, Graffenried BV, Wlfe BMJ (1984) Effects f cyclsprine immunsuppressin in insulin-dependent diabetes mellitus f recent nset. Science 223: Madsbad S, Krarup T, McNair P, Christiansen C, Faber OK, Transbl I, Binder C (1981) Practical clinical value f the C-peptide respnse t glucagn stimulatin in the chice f treatment in diabetes mellitus. Acta Med Scand 210: Kskinen P, Viikari J, Irjala K, Kaihla H-L, Seppal/i P (1986) Plasma and urinary C-peptide in the classificatin f adult diabetics. Scand J Clin Lab Invest 46: Grp L, Pelknen R (1984) Treatment failures: A cmmn prblem in the management f patients with type 2 diabetes. Acta Endcrinlgica 105 [Suppl 262]: Garvey WT, Olefsky JM, Griffin J, Hamman RF, Klterman OG (1985) The effect f insulin treatment n insulin secretin and insulin actin in type 2 diabetes mellitus. Diabetes 34: Hekstra JBL, Van Rijn HJ, Thijssen JHH, Erkelens DW (1982) C-peptide reactivity as a measure f insulin dependency in bese diabetic patients treated with insulin. Diabetes Care 5: Natvig H (1956) Nye Hyde-Vekttabeller fr Nrske Kvinner g Menn. Landsfreningen fr Ksthld g Helse, Osl 14. Gjessing H J, Matzen LE, Faber OK, Frland A (1989) Sensitivity and reprducibility f urine C-peptide as estimate f islet B-cell functin in insulin treated diabetes. Diabetic Med 6: Heding LG (1975) Radiimmunlgic determinatin f human C- peptide in serum. Diabetlgia 11 : Faber OK, Binder C, Markussen J, Heding LG, Naithani VK, Kuzuya H, Blix P, Hrwitz V, Rubenstein AH (1978) Characterizatin f seven C-peptide antisera. Diabetes 27 [Suppl 1]: Hendriksen C, Faber OK, Drejer J, Binder C (1977) Prevalence f residual B-cell functin in insulin treated diabetics evaluated by the plasma C-peptide respnse t intravenus glucagn. Diabetlgia 13: Crssley JT, James AG, Ellitt RB, Berryman CC, Edgar BW (1981) Residual B-cell functin and islet cell antibdies in diabetic children. Pediatr Res 15: Meistas MT, Rendell M, Marglis S, Kwarski AA (1982) Estimatin f the secretin rate f insulin frm urinary excretin rate f C-peptide. Study in bese and diabetic subjects. Diabetes 31: Heding LG (1972) Determinatin f ttal serum insulin (IRI) in insulin treated diabetic patients. Diabetlgia 8: Schmidt FH (1973) Enzymatische Teste zur Schnell-Diagnse. In: Beringer A (ed) 3. Internatinales Dnau-Sympsium fiber Diabetes Mellitus. Verlag W Maudrich, Wien Mfinchen Bern, pp Gjessing H J, Matzen LE, Pedersen PC, Faber OK, Frland A (1988) Insulin requirement in nn-insulin-dependent diabetes mellitus: Relatin t simple tests f islet B-cell functin and insulin sensitivity. Diabetic Med 5: Gjessing H J, Matzen LE, Frland A, Faber OK (1987) Crrelatins between fasting plasma C-peptide, glucagn-stimulated plasma C-peptide, and urinary C-peptide in insulin-treated diabetics. Diabetes Care 10: Welbrn TA, Garcia-Webb P, Bnser A (1981) Basal C-peptide in the discriminatin f Type 1 frm Type 2 diabetes. Diabetes Care 4: Meistas MT, Zadik Z, Marglis S, Kwarski A (1981) Crrelatin f urinary excretin f C-peptide with the integrated cncentratin and secretin rate f insulin. Diabetes 30: Tillil H, Shapir ET, Given BD, Rue P, Rubenstein AH, Gallway JA, Plnsky KS (1988) Reevaluatin f urine C-peptide as measure f insulin secretin. Diabetes 37: Amld-Larsen S, Madsbad S, Kt~hl C (1987) Reprducibility f the glucagn test. Diabetic Med 4: Bnser A, Garcia-Webb P (1981) C-peptide measurement and its clinical usefulness: a review. Ann Clin Bichem 18: Massi-Benedetti M, Burrin JM, Capald B, Alberti KGMM (1981) A cmparative study f the activity f bisynthetic human insulin and prk insulin using the glucse clamp technique in nrmal subjects. Diabetes Care 4: Garvey WI', Revers RR, Klterman OG, Rubenstein AH, Olefsky JM 0985) Mdulatin f insulin secretin by insulin and glucse in Type II diabetes mellitus. J Clin Endcrinl Metab 60: Agner T, Datum P, Binder C (1987) Remissin in IDDM: Prspective study f basal C-peptide and insulin dse in 268 cnsecutive patients. Diabetes Care 10: Meistas MT, Zadik Z, Marglis S, Kwarski A (1981) Crrelatin f urinary excretin f C-peptide with the integrated cncentratin and secretin rate f insulin. Diabetes 30: Hther-Nielsen O, Faber OK, Srensen NS, Beck-Nielsen H (1988) Classificatin f newly diagnsed diabetic patients as insulin-requiring r nn-insulin-requiring based n clinical and bichemical variables. Diabetes Care 11: Received: 21 July 1988 and in revised frm: 2 March 1989 Hans J. Gjessing Svanevej 5 DK-5690 Tmmerup Denmark 311