Judging by this description, they are thinking of testing for MODY 3 (mutation in the HNF1A gene), and perhaps also MODY 1 (mutation in the HNF4A gene -- yes, 'MODY 1', but '4A'). 'MODY' refers to a group of disorders. The MODY's are belong to the broader group of monogenic diabetes. I suggest these tutorials for MODY:
http://www.diabetesgenes.org/content/maturity-onset-diabetes-young (UK site of researchers specialising in MODY)
http://www.diapedia.org/other-types...o-hepatocyte-nuclear-factor-1-alpha-mutations (online diabetes encyclopedia by the Euro. Assn for the Study of Diabetes). Scrutinize their list of clinical features of HNF1A MODY.
Units conversion
here. Apparently the lab is using units of umol/L (micromoles per litre). 232 nmol/L = 0.232 nmol/L; then, 0.232 * 3.0 = 0.70 ng/mL. A commonly cited reference range for serum C-peptide is 1.1-4.4 ng/mL. The reference range values depend both on the test type or technology and on the lab that ran the test.
90% of diagnoses of HNF1A-MODY occur by age 40.
Referring to Diapedia's list of clinical features. The following tests could be ordered to support a request for genetic testing: autoantibodies; glycosuria; CRP test.
CRP is a biochemical marker of inflammation. Of course many people have temporary inflammation due to an infection or injury. Some chronic diseases also cause chronic inflammation. What Diapedia are referring to is that in recent years, it has been established that while CRP is elevated in patients with T1, T2, and HNF4A-MODY (MODY 1), CRP is normal (very low) in patients with HNF1A-MODY (which is the commonest type of MODY). A low value of CRP is not evidence for MODY 3, but a high enough value (in the judgement of a specialist) would rule it out, and possibly rule in MODY 1. (I have read these published studies, and the summary graphs might be of interest to the GP.)
Glycosuria. When blood glucose reaches approx. 10.0 mmol/L, the normal kidney dumps glucose into the urine. I have been dismayed to have people on this forum, and one of my doctors too, declare 10.0 to be within normal. Actually, the "renal threshold" is a last ditch attempt to control the blood level. However, in people with HNF1A-MODY, the renal threshold is rather low. A GP or endo can use a finding of low renal threshold to argue for the expensive genetic testing.
Note the sign of hypersensitivity to sulphonylureas. Patients with MODY 3 need take very small doses of these drugs.