PARKER, Judge.

No appeal lies from an interlocutory order or ruling of a trial judge unless the order or ruling deprives the appellant of a substantial right which he would lose if the order or ruling is not reviewed before the final judgment. Blackwelder v. State of North Carolina Department of Human Resources, 60 N.C. App. 331, 299 S.E. 2d 777 (1983); G.S. 1-277; G.S. 7A-27. An order is interlocutory if it does not determine the issues, but directs some further proceeding preliminary to the final decree. Waters v. Qualified Personnel, Inc., 294 N.C. 200, 240 S.E. 2d 338 (1978). *333 Judge Bulwinkle’s order requiring plaintiff, defendant and Jeffrey to submit to a blood grouping test is an interlocutory order and is not appealable as it does not affect a substantial right. Davie County Department of Social Services v. Jones, 62 N.C. App. 142, 301 S.E. 2d 926 (1983). We elect, however, to treat this appeal as a petition for certiorari, allow it, and pass upon the merits. See Lamb v. Wedgewood South Corp., 308 N.C. 419, 302 S.E. 2d 868 (1983); Patrick v. Hurdle, 16 N.C. App. 28, 190 S.E. 2d 871, cert. denied 282 N.C. 304, 192 S.E. 2d 195 (1972).

General Statute 8-50.1(b) allows the trial court to order a blood grouping test in any civil action in which the question of parentage arises. Defendant argues that as the question of parentage had already been decided, the trial court erred in ordering the blood grouping test. We agree. Plaintiffs guilty plea to the criminal charge of nonsupport of Jeffrey, under G.S. 14-322, is an evidentiary admission of paternity. Wilkes County v. Gentry, 311 N.C. 580, 319 S.E. 2d 224 (1984). See McCormick on Evidence § 265 (2nd ed. 1972). Additionally, plaintiff is barred from raising the issue of paternity by his own allegation in the complaint that Jeffrey was born of his marriage to defendant. Withrow v. Webb, 53 N.C. App. 67, 280 S.E. 2d 22 (1981). See Sutton v. Sutton, 56 N.C. App. 740, 289 S.E. 2d 618 (1982). As the parentage of Jeffrey is not at issue the trial court erred in ordering a blood test pursuant to G.S. 8-50.1, and this order is

Vacated.

Judges Arnold and Wells concur.