PUBLISHED


UNITED STATES COURT OF APPEALS
             FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,             
                Plaintiff-Appellee,
               v.                         No. 11-4336
KRISTEN DEANNA SMITH,
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
        for the District of Maryland, at Greenbelt.
              Roger W. Titus, District Judge.
                 (8:10-cr-00069-RWT-1)

               Argued: September 21, 2012

               Decided: December 17, 2012

   Before DUNCAN, AGEE, and DIAZ, Circuit Judges.



Affirmed by published opinion. Judge Diaz wrote the opinion,
in which Judge Duncan and Judge Agee joined.


                        COUNSEL

ARGUED: William A. Mitchell, Jr., BRENNAN, SULLI-
VAN & MCKENNA, LLP, Greenbelt, Maryland, for Appel-
lant. Hollis Raphael Weisman, OFFICE OF THE UNITED
STATES ATTORNEY, Greenbelt, Maryland, for Appellee.
ON BRIEF: Timothy J. Sullivan, BRENNAN, SULLIVAN
2                   UNITED STATES v. SMITH
& MCKENNA, LLP, Greenbelt, Maryland, for Appellant.
Rod J. Rosenstein, United States Attorney, Baltimore, Mary-
land, for Appellee.


                         OPINION

DIAZ, Circuit Judge:

   Kristen Deanna Smith was convicted by a jury of involun-
tary manslaughter during the commission of an unlawful act
not amounting to a felony, in violation of 18 U.S.C.
§ 1112(a). The district court sentenced her to a term of fifty-
one months’ imprisonment.

   Smith advances three arguments on appeal. First, she con-
tends the district court erred by admitting expert testimony
that she claims exceeded the scope of the government’s pre-
trial disclosure. Second, Smith challenges the sufficiency of
the government’s evidence, arguing that the district court
erred when it denied her motion for judgment of acquittal pur-
suant to Fed. R. Crim. P. 29. Finally, Smith contends the dis-
trict court erred in rejecting one of her proposed jury
instructions. We conclude that the district court committed no
reversible error and that sufficient evidence supported the
jury’s verdict. Accordingly, we affirm.

                              I.

  On appeal from a criminal conviction, we view the evi-
dence in the light most favorable to the government. United
States v. Herder, 

, 358 (4th Cir. 2010).

                              A.

  At about 3:00 a.m. on October 31, 2009, Amber Howard
was driving south from Maryland into the District of Colum-
                       UNITED STATES v. SMITH                          3
bia along the Baltimore-Washington Parkway, a federal area
maintained by the National Park Service. As she approached
D.C., she saw a car’s lights coming toward her from the
northbound side of the highway. She watched that car drive
over the median, flip several times, and crash into the high-
way’s southbound-side embankment.

   Howard pulled over and dialed 911, then ran to check on
the accident. She approached the car and heard a woman
screaming for help. As Howard tried to indicate that help was
on the way, the woman, appellant Kristen Smith, exited the
wrecked vehicle through its rear passenger window and
walked toward Howard. As Smith approached, Howard heard
her say: "I never drink. I never drink. I didn’t want to go out.
I never drink. I only had one drink." Howard also saw the arm
of Smith’s passenger, Jabari Outz, hanging out the car win-
dow.

   While waiting for the police to arrive, a distressed and dis-
oriented Smith repeatedly wandered onto the highway, forc-
ing Howard to pull her out of the road several times. Howard
also smelled the odor of "white liquor" emanating from
Smith. "White liquor," as Howard explained at trial, is alcohol
such as vodka, gin, or tequila, and in Howard’s experience as
a bartender, has a smell distinct from dark liquor or beer.

   United States Park Police Officer Gary Hatch arrived on
the scene at about 3:30 a.m. and found Smith’s car on its side,
leaning against a stone wall. By this time, Outz had been pro-
nounced dead on the scene by emergency medical services.
Officer Hatch, who had some experience as an accident
reconstructionist, analyzed the scene and determined that
Smith’s car had left the northbound roadway, flipped after
crossing the median, and crashed into the stone wall.

  Smith was taken to Prince George’s County Hospital,
where she submitted to a routine blood test.1 U.S. Park Police
  1
   Because the government was unable to establish the chain of custody
of this blood sample, it did not attempt to introduce any evidence of its
blood alcohol results.
4                   UNITED STATES v. SMITH
Officer David Lorde was dispatched to stay with Smith while
she received treatment in the emergency room. He testified
that Smith was writhing in bed and making unsolicited state-
ments, three of which he recalled in particular: "Don’t ever
drink and drive," "I just hope he’s okay," and "Lock me up
and throw away the key."

   Some time later, U.S. Park Police Officer Ernest Patrick
arrived at the emergency room to oversee a second blood
draw, which was conducted at 5:47 a.m. The blood sample
from this draw, which showed a blood alcohol content of .09
grams per 100 milliliters, was furnished to Lucas Zarwell, the
Deputy Chief Toxicologist at the Office of the Chief Medical
Examiner in Washington, D.C.

                              B.

   The government charged Smith in a single-count indict-
ment for homicide during the commission of an unlawful act
not amounting to a felony, in violation of 18 U.S.C.
§ 1112(a). The underlying unlawful act was an alleged viola-
tion of 36 C.F.R. § 4.23(a)(2), which provides that
"[o]perating or being in actual physical control of a motor
vehicle is prohibited while . . . [t]he alcohol concentration in
the operator’s blood or breath is 0.08 grams or more of alco-
hol per 100 milliliters of blood[.]" Notably, the government
chose not to charge Smith with a violation of 36 C.F.R.
§ 4.23(a)(1), which prohibits operating a motor vehicle while
"[u]nder the influence of alcohol . . . to a degree that renders
the operator incapable of safe operation[.]" Unlike the "per
se" § 4.23(a)(2) violation, § 4.23(a)(1) does not require the
government to prove the defendant’s blood alcohol level.

   Deputy Chief Toxicologist Zarwell testified as an expert
witness on the results of the 5:47 a.m. blood sample, stating
that it contained .09 grams of alcohol per 100 milliliters of
blood. Over the defense’s objection, Zarwell also gave gener-
alized testimony about how the human body metabolizes alco-
                    UNITED STATES v. SMITH                    5
hol, including the average duration of alcohol absorption and
rate of elimination. He indicated that typically people con-
tinue to absorb alcohol for "about 30 minutes" after they stop
drinking and that females eliminate alcohol at an average rate
of about .017 grams per 100 milliliters per hour. J.A. 120-21.

   Prior to cross-examination, Smith renewed her objection to
Zarwell’s statements on alcohol metabolization, moving to
strike this line of testimony on the ground that it exceeded the
scope of the pretrial notice provided by the government.
Pointing to a series of letters exchanged between counsel
before trial, the defense charged that the government had rep-
resented that Zarwell’s testimony would be limited to the
results of Smith’s 5:47 a.m. blood test. The defense argued
that without explicit notice that Zarwell would be testifying
about metabolization rates more generally, it was unprepared
to effectively cross-examine Zarwell and unable to realisti-
cally procure a rebuttal witness. Smith did not move for a
continuance or otherwise indicate that she wanted time to pro-
cure her own expert witness regarding blood alcohol absorp-
tion rates, although the court indicated that she could call her
own witness in response to Zarwell’s broadened testimony.

   The district court denied the motion to strike, holding that
the government’s disclosures were sufficient. Zarwell’s
generic testimony, the court explained, was within his area of
expertise and served as necessary background to his testimony
on Smith’s blood test result. Nor did the court find the admis-
sion of Zarwell’s testimony to be unduly prejudicial, since
Smith had the opportunity to cross-examine him and to find
her own toxicology expert.

  The district court also rejected the defense’s alternative
contention that Zarwell’s testimony on generic human alcohol
metabolization was irrelevant as to Smith’s blood alcohol
content at the time of the accident. Even though Zarwell had
not offered an opinion as to Smith’s blood alcohol content at
3:00 a.m., the court reasoned that the jury was not prohibited
6                   UNITED STATES v. SMITH
from making inferences on that issue based on Zarwell’s
generic metabolization testimony and the results of the 5:47
a.m. test.

   During cross-examination, Zarwell confirmed that his
blood alcohol analysis showed the quantity of alcohol in
Smith’s blood only at the time of the 5:47 a.m. test, not
beforehand. He also conceded, notwithstanding his earlier tes-
timony about typical alcohol absorption and elimination rates,
that those rates are highly variable among individuals. Zar-
well stated that although he would have been able to conduct
an individualized analysis of Smith’s absorption and elimina-
tion rates, he had not done so. Zarwell also confirmed that he
had not performed a retrograde extrapolation of Smith’s blood
alcohol level at the time of the crash and did not offer any
opinion about her blood alcohol level at that time.

   At the close of the government’s case in chief, Smith
moved for a judgment of acquittal under Fed. R. Crim. P. 29,
arguing that the evidence produced by the government was
insufficient to show her blood alcohol level exceeded .08 at
the time of the accident, almost three hours before the blood
test. The district court denied the motion, concluding that
based upon the 5:47 a.m. blood test result, the evidence of
Smith’s erratic driving and behavior, and the statements she
made at the hospital, a rational jury could reasonably infer
that she had violated § 4.23(a)(2). Smith offered no evidence
and renewed her motion for judgment of acquittal, which the
district court again denied.

   At the charge conference, Smith requested several supple-
mental jury instructions, one of which proposed to instruct the
jury, in relevant part, as follows:

    As you heard, the rates of alcohol absorption and
    elimination can vary between persons. Therefore, the
    practice of extrapolating a person’s blood alcohol
    level at the time of driving from a test of a blood
                      UNITED STATES v. SMITH                    7
    sample taken at a later time requires careful consid-
    eration of many factors . . . . I instruct you that you
    should not attempt to extrapolate the blood alcohol
    of the accused at the time of driving from the result
    of a blood test from samples taken at a later time
    unless sufficient evidence has been presented to you
    with regard to the aforementioned factors . . . . You
    may not infer from the test of defendant’s blood
    samples taken at 5:47 a.m. on October 31, 2009, in
    this case—without more, as I have described
    above—what defendant’s blood alcohol content at
    the time of driving around 3:00 a.m. might have
    been.

S.J.A. 3; J.A. 141.

   The district court rejected this instruction. It explained that
the jury already knew that there was no piece of evidence,
standing alone, showing that Smith’s blood alcohol content
exceeded .08 at the time of the crash—an element the existing
jury instructions already established was essential to the
crime. But because there were other facts in the record from
which the jury might reasonably infer the § 4.23(a)(2) viola-
tion, the court allowed the jury to draw those inferences.

  The jury returned a guilty verdict on the sole count of the
indictment. Prior to sentencing, Smith renewed her motion for
judgment of acquittal and moved for a new trial. The district
court denied both motions and imposed its sentence. This
appeal followed.

                               II.

  The issues before us are (1) whether the district court erred
in permitting the government’s toxicology expert to testify
about generic alcohol metabolization rates; (2) whether Smith
was entitled to a judgment of acquittal due to insufficient evi-
dence; and (3) whether the district court erred in refusing to
8                        UNITED STATES v. SMITH
give Smith’s requested jury instruction concerning blood
alcohol level extrapolation. We consider each issue in turn.
                                     A.
  Smith contends the district court erred in permitting the
government’s toxicology expert to testify about generic alco-
hol metabolization rates. We review the district court’s evi-
dentiary rulings for abuse of discretion, United States v.
Basham, 

, 325 (4th Cir. 2009), and generally will
not reverse absent a showing of prejudice, United States v.
Durham, 

, 592 (4th Cir. 1963).
   Smith argues that she was unfairly surprised by toxicologist
Lucas Zarwell’s testimony regarding average human alcohol
metabolization rates because this testimony exceeded the
scope of the pretrial notice provided by the government pur-
suant to Fed. R. Crim. P. 16. As she did at trial, Smith points
to the series of letters exchanged between counsel during dis-
covery that comprised the parties’ Rule 16 communications.
J.A. 351-61. The government’s initial written disclosure
included Zarwell’s curriculum vitae and named him as the
likely toxicology expert. In response, Smith’s counsel wrote:
"It is assumed from your discovery response that the expert
evidence would be limited to testimony . . . that [Smith’s 5:47
a.m.] blood sample revealed an ethanol level of .09%." J.A.
359. The government’s reply confirmed that Smith’s charac-
terization was "correct as to the toxicology expert testimo-
ny[.]" J.A. 361. Smith argues that since Zarwell’s testimony
was not confined to the results of the blood test, as the letters
suggested it would be, the district court abused its discretion
by admitting it. As a result, Smith claims she was unable to
effectively cross-examine Zarwell on the intricacies of
"relation-back" science2 or prepare her own expert to rebut
Zarwell’s testimony.
   2
     "Relation-back" science attempts to extrapolate—or relate back—the
results of a blood alcohol test administered after a person’s arrest to his
or her blood alcohol level at the time of operation of the vehicle. See
Ransford v. District of Columbia, 

, 186 (D.C. 1990). As both
parties have noted, the reliability of relation-back science is up for debate.
Appellee’s Br. at 29-30; J.A. 114.
                        UNITED STATES v. SMITH                             9
   The government echoes the district court’s justification for
admitting the evidence, arguing that Zarwell gave no testi-
mony about Smith’s personal alcohol elimination rate and that
Zarwell’s testimony concerning typical human alcohol meta-
bolization was general background information within the
scope of both the notice and his expertise. It notes that Smith
never objected to Zarwell’s qualifications as a toxicology
expert and that, having sat down with Zarwell before trial for
an in-person interview, Smith’s counsel had ample opportu-
nity to prepare for cross-examination. Finally, the government
asserts that even assuming error, Smith has failed to demon-
strate how she suffered any prejudice as a result of the testi-
mony or the wording of the government’s pretrial disclosure.

   Federal Rule of Criminal Procedure 16(a)(1)(G) requires
the government to give, at the defendant’s request, a written
summary of any expert testimony that it intends to use during
its case-in-chief at trial. This summary "must describe the wit-
ness’s opinions, the bases and reasons for those opinions, and
the witness’s qualifications." Fed. R. Crim. P. 16(a)(1)(G). As
the rule’s Advisory Committee Notes explain, Rule
16(a)(1)(G) "is intended to minimize surprise that often
results from unexpected expert testimony . . . and to provide
the opponent with a fair opportunity to test the merit of the
expert’s testimony through focused cross-examination." Fed.
R. Crim. P. 16(a)(1)(G) Advisory Comm. Note to the 1993
amendment.

  On the one hand, we do not fault Smith for taking issue
with the government’s less than fulsome pretrial summary of
Zarwell’s planned expert testimony.3 On the other hand, con-
  3
   To be fair, the government’s Rule 16 disclosure should be read in con-
text; it was drafted in part to inform Smith that it would not be introducing
the results of the earlier blood alcohol test, but would only be introducing
the results of the second test. At trial, the government contended that one
reason it sought to elicit Zarwell’s generic testimony regarding blood alco-
hol absorption was Smith’s sole defense—articulated during opening
10                     UNITED STATES v. SMITH
sistent with the government’s Rule 16 disclosure, Zarwell
declined to offer any opinion on Smith’s personal metaboliza-
tion rate, and did not attempt to extrapolate what her blood
alcohol content might have been at 3:00 a.m. And although
full disclosure by the government would have been more in
keeping with the spirit of Rule 16, we think it fair to charac-
terize Zarwell’s testimony on typical human alcohol absorp-
tion and elimination rates as generic background information
that fell within the scope of Zarwell’s expertise.

   In any event, we need not decide whether the district court
erred in concluding that the Government did not violate Rule
16(a)(1)(G), because any error was harmless. In addition to
showing the district court’s error, a defendant seeking reversal
under Rule 16(a)(1)(G) must also "demonstrate prejudice
resulting from the district court’s decision to admit the con-
tested testimony." United States v. Buchanan, 

,
526 (8th Cir. 2010); see also United States v. Charley, 

, 1261-62 (10th Cir. 1999) (affirming a district court
decision despite a Rule 16 violation, due to absence of preju-
dice to defendant).

   Smith fails to make that showing here. Although Smith
claims that the government’s incomplete Rule 16 disclosure
prevented her from effectively cross-examining Zarwell on
the intricacies of relation-back science, Zarwell never offered
any such evidence. Further, Smith interviewed Zarwell prior
to the trial, and extensively cross-examined him at trial
regarding the numerous factors that determine an individual’s

statements—that the toxicology report only reflected Smith’s blood alco-
hol level at the time it was taken and was irrelevant to her blood alcohol
level at the time of the accident. See United States v. Basic Constr. Co.,

, 574 (4th Cir. 1984) (observing that while the practice of
permitting evidence in the government’s case-in-chief based on arguments
made during a defendant’s opening statement should be "discouraged," it
may be harmless where the defendant "followed through on its articulated
defense").
                      UNITED STATES v. SMITH                       11
blood alcohol absorption rate, the nuances of his generalized
direct testimony, and whether it was possible that a person’s
blood alcohol level would continue to increase for a few hours
after consumption.4 And to the extent Smith disagreed with
Zarwell’s testimony regarding general metabolization rates,
the district court gave her ample opportunity to call her own
rebuttal expert. Smith simply chose not to pursue that avenue
or ask for a continuance to consider it.

   For these reasons, we conclude that the district court did
not commit reversible error in permitting Zarwell’s expert tes-
timony.

                                 B.

   We next consider Smith’s argument that she was entitled to
a judgment of acquittal because the government offered insuf-
ficient evidence to support her conviction. We review de novo
the district court’s decision to deny a defendant’s Rule 29
motion for judgment of acquittal. United States v. Smith, 

, 216 (4th Cir. 2006). On an appeal challenging the
sufficiency of evidence, we assess the evidence in the light
most favorable to the government, and the jury’s verdict must
stand unless we determine that no rational trier of fact could
have found the essential elements of the crime beyond a rea-
sonable doubt. United States v. Young, 

, 355 (4th
Cir. 2010).

   Smith concedes that the government presented evidence
that she was under the influence of alcohol at the time of the
accident. She also concedes that the government’s evidence
established that her blood contained .09 grams of alcohol per
100 milliliters at 5:47 a.m., nearly three hours after the crash.
Smith contends, however, that the government did not offer
sufficient evidence upon which a rational finder of fact could
  4
   Indeed, some of the testimony Smith elicited from Zarwell on cross-
examination was favorable to her case.
12                   UNITED STATES v. SMITH
have determined beyond a reasonable doubt that, at the time
she was operating her vehicle, her blood alcohol concentra-
tion was .08 percent or more, as a 36 C.F.R. § 4.23(a)(2) "per
se" violation requires. Absent such direct evidence, Smith
insists, she was entitled to a judgment of acquittal.

   The government responds that its evidence was sufficient
to support the conviction. It argues that the fact that Smith had
a blood alcohol content exceeding .08 percent within a rea-
sonable period of the time after driving sufficed to show a
violation of the § 4.23(a)(2) "per se" offense, without any
need for relation-back evidence, which it argues is unreliable
and impractical to obtain. While acknowledging that
§ 4.23(a)(2) does require a showing that a defendant’s blood
alcohol content exceeded .08 at the time of driving, the gov-
ernment suggests it would be absurd to hold that the "per se"
offense requires the government to prove precisely the blood
alcohol level at the time of driving. Instead, the government
asks us to hold that a blood alcohol test taken within a reason-
able time after driving satisfies the "per se" statute. Finally,
the government points to other evidence supporting the jury’s
finding that Smith violated § 4.23(a)(2): evidence that Smith
was driving recklessly, testimony that she was behaving errat-
ically and that she smelled of "white liquor," and statements
she made at the scene of the accident and at the hospital about
her own drinking and driving.

   Section 4.23(a)(2) provides that "[o]perating or being in
actual physical control of a motor vehicle is prohibited while
. . . [t]he alcohol concentration in the operator’s blood or
breath is 0.08 grams or more of alcohol per 100 milliliters of
blood[.]" Unlike some comparable state statutes, § 4.23(a)(2)
sets no explicit time limit for the taking of a blood alcohol test
that may be used at trial to show a defendant’s alcohol con-
centration. Compare 36 C.F.R. § 4.23(a)(2), with Va. Code.
Ann. § 18.2-268.2A (setting a three-hour limit between "the
offense" and the taking of the sample), and Md. Code Ann.,
Cts. & Jud. Proc. § 10-303(a)(2) (setting a two-hour limit
                    UNITED STATES v. SMITH                   13
after the person has been "apprehended"). Section 4.23(a)(2)
is also silent as to the regulation’s proof requirements, and we
have found no published authority from our sister circuits on
this question, which has become the subject of some debate
among other lower courts.

   Some courts have interpreted § 4.23(a)(2) to mean that the
government must directly prove a defendant’s blood alcohol
content at the time he or she was driving, often through
relation-back testimony. For example, the United States Dis-
trict Court for the District of Nevada has twice refused to find
later-administered breath tests sufficient to support a
§ 4.23(a)(2) conviction. See United States v. French, No.
2:08-MJ-726-GWF, 

(D. Nev. Apr. 10,
2010) (unpublished); United States v. Stout, No.
2:09–MJ–00146–GWF, 

(D. Nev. Dec. 28,
2009) (unpublished). As the Stout court reasoned:

    Unlike some state DUI laws, 36 C.F.R. § 4.23(a)(2)
    does not make it unlawful to have a blood alcohol
    level above the legal limit within a specified time
    after operating a motor vehicle. Nor does it contain
    a presumption regarding the person’s blood alcohol
    at the time he was operating or in physical control of
    a vehicle based on subsequently obtained breath or
    blood test results. Because there is no presumption
    based on the test results, the Government is required
    to prove that a defendant’s blood alcohol content
    was above the legal limit at the time of operating the
    vehicle and not merely at the time the breath or
    blood sample was taken.

, at *6. Courts interpreting § 4.23(a)(2) to
require relation-back evidence have also noted the availability
to the government of proceeding under § 4.23(a)(1), which
has no blood alcohol content requirement. See United States
v. Wight, 

, 402 (D. Colo. 1995). By choosing
14                  UNITED STATES v. SMITH
to proceed on the "per se" violation, the Wight court
explained, the government

     had an obligation under the regulation to establish
     the alcohol concentration at the time of driving or
     actual physical control. The test result at 8:27 a.m.
     was insufficient, in and of itself, to establish what
     Defendant’s concentration was at 6:15 a.m., or even
     at 7:00 a.m. Once [the government] chose to proceed
     on the "per se" violation, it had to present qualified
     evidence that "related back" the test results to the
     time of driving or actual physical control.

other courts dealing with similar "per se" stat-
utes have held that relation-back testimony is unnecessary to
prove the offense. And where, as here, those statutes impose
no time limit on the blood alcohol test, courts have also regu-
larly found that violations may be established as long as the
government produces evidence of blood alcohol levels within
a reasonable time after driving. See, e.g., Commonwealth v.
Colturi, 

, 500 (Mass. 2007); State v. McGo-
wan, 

, 844 (Mont. 2006); 

.

   For example, in a case cited by the district court below, the
Montana Supreme Court concluded that a comparable state
"per se" statute could not be read literally "to require law
enforcement officers to determine a person’s alcohol concen-
tration while driving . . . , as it would be impossible for an
officer to administer a test while the suspect was driving."

. Nor, McGowan concluded,
should the government be required to meet what it character-
ized as the "impossible burden" of presenting relation-back
evidence. 

extrapolation, the court explained,
would require difficult-to-obtain evidence falling within a
defendant’s constitutional right to remain silent, such as when
                       UNITED STATES v. SMITH                         15
and in what amounts the defendant consumed alcohol, and
whether the defendant had recently consumed any food. 

the same conclusion, pointed out that
even if the prosecution could obtain this information, "conclu-
sive evidence of the blood alcohol content at the time of driv-
ing could still not be offered to the jury . . . because the rate
of absorption of alcohol varies between individuals." Rans-

. These courts have concluded that legis-
latures could not have intended to impose such evidentiary
hurdles on the prosecution. Id.; 

-
45.

   We need not decide whether, on its own, a blood alcohol
test taken within a "reasonable time" after driving can satisfy
the proof requirement of § 4.23(a)(2)’s "per se" offense.
Rather, it is enough for us to say that the government may, in
some circumstances, establish a "per se" violation without
direct evidence of the defendant’s blood alcohol content while
actually driving and without introduction of relation-back evi-
dence.

   In the instant case, we are satisfied that a rational finder of
fact could have determined beyond a reasonable doubt that
Smith violated the "per se" regulation. Even if Smith is cor-
rect that, standing alone, her 5:47 a.m. blood alcohol result
was insufficient to establish the violation, this evidence did
not actually stand alone. The government presented myriad
other evidence supporting the jury’s conclusion that Smith’s
blood alcohol level was over the legal limit while she was
driving. Most notably, Zarwell’s unrebutted testimony about
typical alcohol absorption durations and elimination rates
established that it was extremely unlikely that Smith could
have registered a .09 percent blood alcohol content at 5:47
a.m. without having exceeded the .08 percent threshold at the
time of the crash nearly three hours earlier.5 Even accounting
  5
   As the district court noted and as the government told the jury in its
closing argument, there was no evidence that Smith had consumed any
16                     UNITED STATES v. SMITH
for the wide range of individual alcohol metabolization rates
to which Zarwell attested, and even assuming that Smith
absorbs and eliminates alcohol much more slowly than the
average woman, a rational juror could still have concluded
beyond a reasonable doubt that a "per se" violation had
occurred.

   This is particularly true, as the district court noted, given
the abundant other indicia of Smith’s guilt. The evidence
established that Smith was driving erratically and that she
flipped her car over the highway’s median strip. Howard testi-
fied that Smith was behaving erratically, wandering into the
road, and that she smelled strongly of "white liquor." Smith
also made statements to two witnesses about her own drinking
and driving. To be sure, none of this evidence points defini-
tively to Smith’s precise blood alcohol level at the time of the
accident. When coupled, however, with the result of the 5:47
a.m. blood alcohol test and Zarwell’s generic metabolization
testimony, this evidence could lead a rational juror to deter-
mine beyond a reasonable doubt that Smith had violated the
regulation’s .08 threshold.

  Accordingly, we conclude that Smith was not entitled to a
judgment of acquittal.

                                   C.

   Finally, we address Smith’s contention that the district
court erred in refusing to give her requested jury instruction
concerning blood alcohol level extrapolation. We review a
district court’s decision to give or refuse to give a jury

alcohol between the time of the accident and the time her blood was
drawn. The jury could therefore reasonably infer that any alcohol that
appeared in her 5:47 a.m. blood sample had been in her system at the time
she was operating the vehicle, and that apart from the absorption of
previously-consumed alcohol that Zarwell had described, there was no
reason why Smith’s blood alcohol concentration would have increased
during that interim period.
                     UNITED STATES v. SMITH                     17
instruction for abuse of discretion, and reverse only when the
rejected instruction "(1) was correct; (2) was not substantially
covered by the court’s charge to the jury; and (3) dealt with
some point in the trial so important, that failure to give the
requested instruction seriously impaired the defendant’s abil-
ity to conduct his defense." United States v. Passaro, 

, 221 (4th Cir. 2009) (internal quotation marks omit-
ted). "Moreover, we do not view a single instruction in isola-
tion; rather we consider whether taken as a whole and in the
context of the entire charge, the instructions accurately and
fairly state the controlling law." 

omitted).

   Smith contends that the district court erred in refusing to
instruct the jury that it could not infer her guilt from the result
of her 5:47 a.m. blood test, "without more." Absent this
instruction, Smith argues, the jury was left to engage in con-
jecture and speculation about the results of the blood sample
and its evidentiary value to the elements of the crime charged.
The government responds that the court’s instructions were
complete and correct, and that they sufficiently explained to
the jury that it could decide whether Smith had a .08 percent
or more blood alcohol content at the time of the crash, based
on all the evidence it heard.

   We conclude that the district court did not abuse its discre-
tion in refusing to give Smith’s proposed instruction, because
that instruction was not necessarily correct and, in any event,
was "substantially covered by the court’s charge to the jury."

. As the district court noted, Smith’s
proposed instruction that the jury could not infer guilt from
the 5:47 a.m. blood test, "without more," could easily have led
to confusion about what other evidence the jury was allowed
to consider. By the same token, the proposed instruction also
improperly implied that, beyond the 5:47 a.m. blood test,
there was no other evidence supporting an inference of guilt.

   The district court’s instructions set forth the elements of the
crime and made clear the government’s burden of proving
18                   UNITED STATES v. SMITH
beyond a reasonable doubt that at the time of the accident
Smith’s blood alcohol content was .08 or higher. Even as it
recognized that there was no direct evidence that Smith’s
blood alcohol content exceeded the .08 threshold while she
was driving, the district court rightly concluded that there
were facts in the record from which the jury might reasonably
infer the violation and instructed the jury that it was free to
either make that inference or not. Ultimately, when "[t]aken
as a whole and in the context of the entire charge, the instruc-
tions accurately and fairly state[d] the controlling law." Pas-

. As a result, the district court did not
abuse its discretion in denying Smith’s proposed instruction.

                               III.

   In sum, the district court did not abuse its discretion in
admitting the toxicologist’s generic testimony on alcohol
metabolization. Nor was Smith entitled to judgment of acquit-
tal, because the government’s evidence was sufficient to sup-
port the jury’s verdict. Finally, the district court did not abuse
its discretion in denying Smith’s proposed jury instruction.
Accordingly, we affirm the judgment of the district court.

                                                    AFFIRMED