We think that the question raised by de Vries and Bakker (1) in regard to our study (2) is appropriate. It is important to find the most convenient and adequate method to estimate insulin resistance (IR) in transplant recipients without necessarily carrying out an oral glucose tolerance test. Also, because the IR observed in transplant recipients is a common side effect of treatment with prednisolone, this issue is probably of interest for most physicians.

Accordingly, we have validated the insulin sensitivity index (ISI) suggested by McAuley et al. (3), based on fasting serum insulin and triglycerides (TG) (ISIMcAULEY = Exp [2.63–0.28 × ln (insulin) − 0.31 × ln (TG)]), against the results from our glucose clamp studies. The equation proposed by McAuley et al. correlated significantly and reasonably well with the clamp-derived ISI (Spearman’s correlation; r = 0.43, P = 0.004) (Table 1). This is superior to the results from the other ISIs based on either fasting insulin (insulin resistance index [IRI]: IRIINS0; r = −0.32) or fasting glucose and insulin (IRIHOMA; r = −0.30) (4).

In addition, we calculated the correlation between our clamp results and the Quantitative Insulin Sensitivity Check Index: ISIQUICKI = 1/[logI0 + logG0], where I0 is the fasting insulin (μU/ml) and G0 is the fasting glucose (mg/dl) (5). This equation also correlated significantly with the clamp-derived ISI (r = 0.30, P = 0.049) similar to the IRIINS0 and the IRIHOMA.

We therefore suggest that the ISIMcAULEY is the most appropriate formula to use when estimating insulin action in steroid-treated patients when fasting insulin, glucose, and triglyceride concentrations are known. However, our previously proposed formula (ISITX = 0.208–0.0032 × BMI −0.0000645 × Ins120 −0.00375 × Gluc120) remains superior to other known estimates of insulin action when the 2-h glucose and insulin concentrations are available.

Table 1—

Correlation of ISICLAMP to surrogate measures of insulin sensitivity and insulin resistance

Spearman’s correlation (r)
IRIINS120 2-h Insulin −0.45* 
IRIAUCGI AUC glucose/AUC insulin −0.44* 
ISIMATSUDA Composite index 0.41* 
ISITX Modified Stumvoll index 0.58† 
IRIINS0 Fasting insulin −0.32‡ 
IRIHOMA Homeostasis model assessment −0.30‡ 
ISIQUICKI Quantitative insulin sensitivity check index 0.30‡ 
ISIMcAULEY  0.43* 
Spearman’s correlation (r)
IRIINS120 2-h Insulin −0.45* 
IRIAUCGI AUC glucose/AUC insulin −0.44* 
ISIMATSUDA Composite index 0.41* 
ISITX Modified Stumvoll index 0.58† 
IRIINS0 Fasting insulin −0.32‡ 
IRIHOMA Homeostasis model assessment −0.30‡ 
ISIQUICKI Quantitative insulin sensitivity check index 0.30‡ 
ISIMcAULEY  0.43* 
*

P < 0.01;

†

P < 0.001;

‡

P < 0.05. AUC, area under curve.

View Large
1
de Vries APJ, Bakker SJL: Insulin resistance after renal transplantation (Letter).
Diabetes Care
 
25
:
1259
–1260,
2002
2
Hjelmesæth J, Midtvedt K, Jenssen T, Hartmann A: Insulin resistance after renal transplantation: impact of immunosuppressive and antihypertensive therapy.
Diabetes Care
 
24
:
2121
–2126,
2001
3
McAuley KA, Williams SM, Mann JI, Walker RJ, Lewis-Barned NJ, Temple LA, Duncan AW: Diagnosing insulin resistance in the general population.
Diabetes Care
 
24
:
460
–464,
2001
4
Matthews D, Hosker J, Rudenski A, Naylor B, Treacher D, Turner R: Homeostasis model assessment: insulin resistance and β-cell function from fasting plasma glucose and insulin concentrations in man.
Diabetologia
 
28
:
412
–419,
1985
5
Katz A, Nambi SS, Mather K, Baron AD, Follmann DA, Sullivan G, Quon MJ: Quantitative insulin sensitivity check index: a simple, accurate method for assessing insulin sensitivity in humans.
J Clin Endocrinol Metab
 
85
:
2402
–2410,
2000

Address correspondence to Jøran Hjelmesæth, MD, Medical Department, Vestfold Central Hospital, Boks 2168, 3103 Tønsberg, Norway. E-mail: [email protected].

DIABETES CARE
2002