Prenatal Urine Testing

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					  Prenatal Urine Testing

   Mary Ann Rhode MS, CNM
Exempla Certified Nurse Midwives
       Denver, Colorado
A Sacred Cow of Obstetrics
        History of Urine Testing Practices
1843   Relationship between urinary protein and eclampsia noted

1903 Protein testing suggested by Edgar in The Practice of

1917 Screening for glycosuria proposed in Williams

1948 Urine testing was being taught to granny midwives in the
     movie "All My Babies" produced by Columbia University

1970   Nearly universal, expanded to include other substances such
       as nitrites and leukocyte esterase
Traditional Purpose of
Prenatal Urine Testing

Screen for:

Gestational diabetes


Urinary tract infection
Gestational Diabetes Considerations

 Urine testing for GDM, as the primary screening test,
                  not used for decades

  Diabetics no longer regulate insulin based on urine

       Glucose tolerance testing is widely accepted as
             the best screening method
             Pre-eclampsia Considerations
No current effective screening method for early detection

Many early markers identified but either impractical to use or not
  predictive enough

Urinary placental growth factor (PlGF)
  Most recently studied marker for preeclampsia
   Tested between 21-32 weeks gestation
   "Decreased urinary PIGF at mid gestation is strongly associated
  with subsequent early development of preeclampsia." Levine 2005
       Pre-eclampsia Considerations

Protein testing is for diagnosis, 24 hour urine collection is
  preferred method

Proteinuria rarely precedes an elevation in blood pressure

"Dipstick urinalysis cannot be relied on either to
  detect or to exclude the presence of proteinuria
  in pregnant women."       Kuo 1992
    Urinary Tract Infection Considerations
Type of infection

Cystitis - 1 - 2 % incidence

Pyelonephritis - 1-2 % incidence

Asymptomatic bacteriuria

   •2 - 7 % incidence
   •20-30 % progress to pyelonephritis without treatment

    Less than 1 % acquire bacteriuria in pregnancy after initial
Symptomatic vs asymptomatic
• Sensitivities of tests vary based on presence or
  absence of symptoms

Pregnant vs non-pregnant
• Sensitivities vary by patient population
• Many symptoms of pregnancy and UTI are similar
• Prenatal urine screening is mostly for
  asymptomatic bacteriuria
• Urine culture is considered the "gold standard" for
Current Standard Screening Practices

       BP check each prenatal visit

       Urine dipstick testing each visit

       Glucose challenge test at 24-29 weeks

       Urinalysis or urine culture at first visit
                  Recommended Guidelines
“During each regularly scheduled visit, the health care provider
  should evaluate the woman’s blood pressure, weight, urine for
  the presence of protein and glucose levels, uterine size for
  progressive growth and consistency with the estimated date of
  delivery, and fetal heart rate.”    Guidelines for Perinatal Care, 2002

Routine testing:
•   Hct or Hgb levels
•   Urinalysis, including microscopic examination
•   Urine testing to detect asymptomatic bacteriuria (eg, urine culture)
•   Determination of blood group and CDE (Rh) type
•   ABS
•   Determination of immunity to rubella virus
•   Syphilis screen
•   Cervical cytology (as needed)
•   Hepatitis B virus surface antigen
•   HIV antibody testing
    GDM Screening Recommendations

• Do not recommend universal screening for GDM but strongly
  recommend screening pregnant women in high-prevalence

ACP, ADA, & Third International Workshop Conference on
  Gestational Diabetes
• Recommend universal screening for GDM at 24-28 weeks using
  a 1-hour glucose tolerance test

Guide to Clinical Preventive Services 3rd edition, 2002
• Insufficient evidence to recommend for or against routine
  screening for GDM
           Preeclampsia Screening
ACOG         Recommendations
• BP measurements at initial visit
• Every 4 weeks until 28 weeks gestation
• Every 2-3 weeks until 36 weeks gestation
• Every week thereafter
Canadian Task Force on Periodic Health Examination
• Systolic & diastolic BP at the first prenatal visit
  and periodically throughout the rest of pregnancy
Guide to Clinical Preventive Services. 3rd edition, 2002
• BP measurement at each visit
• Further diagnostic evaluation, including BP monitoring
  and urine testing for protein when indicated
    Asymptomatic Bacteriuria Screening
• Urinalysis, including microscopic examination and infection screen at
  first visit
• Additional evaluation such as culture, as needed, based on history and
  physical exam

Canadian Task Force on Periodic Health Examination
• Urine culture at 12-16 weeks of pregnancy
  (based on research that showed identification of 80 % who will
  eventually have ASB in pregnancy)

Guide to Clinical Preventive Services          3rd edition, 2002
• Urine culture for all pregnant women at 12-16 weeks gestation
• Routine screening for ASB with LE or nitrite testing in pregnant
  women not recommended
        Questions about Urine
        Reagent Strip Testing

• Redundant testing
• Lack of evidence of improved
  pregnancy outcome with routine testing
• Testing sources of error - tests need to
  be accurate and reliable, i.e. sensitive
  and specific
Problems with Urine Reagent Strip Testing

• Different thresholds between dipstick urinalysis and 24
  hour urinary protein excretion
  (Thresholds for dipstick test and standard 24 hour urine assay are only
  equivalent if the 24 hour urine specimen is about 1000 mL)

• Sensitivity and specificity

• Varying concentration of protein in random specimens

• Observer error
              Sensitivity and Specificity Definitions
Term                                                   Definition                                         Formula

Sensitivity                             Proportion of persons with                                          a
                                        condition who test positive                                        a+c

Specificity                             Proportion of persons without                                        d
                                        condition who test negative                                         b+d

Positive predictive value               Proportion of persons with positive test                            a
                                        who have condition                                                 a+b

Negative predictive value               Proportion of persons with negative test                             d
                                        who do not have condition                                           c+d

                            Condition                  Condition                    Legend:
                            Present                     Absent
                                                                                    a = true positive
Positive test                  a                            b
                                                                                    b = false positive
Negative test                  c                            d
                                                                                    c = false negative

                                                                                    d = true negative
                       From: U.S. Preventive Task Force Guide to Clinical Preventive Services, 3rd. Ed.
Poor sensitivity
• Misses cases - the false negative rate
• Leads to delayed treatment

Poor specificity
• Identifies healthy people as having a
  condition - the false positive rate
• Leads to over-investigation, over-treatment
             Urine Reagent Strip Sensitivities*
Test                         Sensitivity                    Specificity                      + predictive value
Culture                        100

Gram stain                      83-92 %                         89-95                                  17-28

Urinalysis                      8 -25 %                         99                                     37-40

Urinalysis w/                   75-83                           59-60                                  4.5
bacteria or

Nitrites                        19-68                          99                                      69-90

Leukocyte                       17                             97                                      12

LE and nitrites                 13                           100                                       100

LE or nitrites                  50                             97                                      27

Protein, nitrites               8-33                           91                                      18
blood, LE

                 *   From: Bachman, Tincello, and Etherington, rounded to nearest whole percentage point
        Sources of False Positive Results

•   Dipstick left too long in concentrated urine
•   Gross hematuria
•   Pus, semen, vaginal secretions
•   Penicillin, sulfonamides, tolbutamide use
•   False + for protein if refrigerated > 24 hours
     Sources of False Negative Results

• Nonalbumin or LMW proteins

• High levels of ascorbic acid or aspirin

• Dilute urine ( > 1.015)

• Nitrite false negatives are common due to: Lack of dietary
  nitrates, insufficient urinary nitrate levels due to diuretics, low
  urinary retention, infection due to organisms that don't produce
  nitrites, Staphyloccocus sp. , Enterococcus sp., Pseudomonas

• Increased for WBC’s/RBC’s if refrigerated > 24
    Variation in Protein Concentration in
            Random Specimens
• Contamination (false positive)
• Exercise           (increased excretion)
• Posture          (increased excretion in upright position)
• Osmolality       (increased false positives)
• Urinary pH ( pH > 7.5)
• Timing of collection - sensitivity improved with first
  morning specimen
• Different assay methods, pattern of urinary protein
  composition (some proteins may be associated more with
                     Observer Error

• More false positives with less trained staff
• Most common error is to "round up"
• Training can reduce false positive rate
• Specificity may deteriorate if strips stored in open containers
• False negative rate unchanged by training, possibly due to
• Use of automated devices can improve accuracy
Obstacles to Changing Current Practice

 • We might miss something
 • It’s too slow if we have to get a specimen
 • Somebody might die
 • What will the other care providers think
 • We’ve always done it that way
 • Remember, there are legal issues to consider
 • What about renal disease?
            Sources of Benign Proteinuria

 •   Dehydration                          •   Inflammatory process
 •   Emotional status                     •   Intense activity
 •   Fever                                •   Acute illness
 •   Heat injury                          •   Orthostatic disorder

Corral MF. Proteinuria in adults: a diagnostic approach. American Family
   Physician, 2000.
Some Pathologic Causes of Proteinuria
   • Primary glomerulonephropathy
      – ex. glomerulonephritis
   • Secondary glomerulonephropathy
      – ex. diabetes
            collagen vascular disease
   • Drug associated
   • Hemoglobulinuria
   • Multiple myeloma
                  Renal Disease Considerations

•   “Fewer than 2 % of positive dipsticks have serious and treatable urinary tract
    disorders.” Corral MF. Proteinuria in adults: a diagnostic approach. American Family Physician, 2000.
•   “It is likely that this occurrence of mild, intermittent proteinuria in the general
    population makes routine screening ineffective. It has been
    suggested that screening of urine be reserved for populations at high
    risk of renal disease such as patients with diabetes or hypertension.”
    Woolhandler S. Dipstick urinalysis screening of asymptomatic adults for urinary tract disorders. JAMA, 1989.

•   Acute renal failure in pregnancy                  - 1 : 20,000

•   Microalbuminuria – excretion below detection level of urine dipsticks

•   Persistent rates of 20 micrograms/minute predictive of diabetic neuropathy &
    chronic renal disease
Routine prenatal urine screening
• Done at every prenatal visit

Indicated prenatal urine testing
• First prenatal visit
• Whenever clinical symptoms are present
• High risk conditions
             Why Continue Urine
            Reagent Strip Testing?
• Only testing available for many years
• Easy and quick, compared to 24 hour urine
• Requires little technical expertise
• Less expensive than urine culture or 24 hour urine
• No "absolute" proof of safety of indicated testing
• Sometimes the information is needed, i.e. there is
  an indication for the test
Evidence to Discontinue Routine Screening
• Changing practice at other institutions

• Public Health Service Expert Panel on
   the Content of Prenatal Care, 1989

• US Preventive Services Task Force Guide to
  Clinical Preventive Services, 1996, 2004

• Previous research
              Asymptomatic Bacteriuria Studies
Lenke             1981     Recommended use of routine culture for women at risk of
                           for recurrent pyelonephritis because positive cultures aren't
                           accurately predicted by microscopic urinalysis or nitrite testing

Robertson         1988     Nitrite or leukocyte esterase alone not sensitive enough to detect
                           ASB, nitrites plus LE may be better

Etherington       1993     Combination of leukocyte esterase, nitrite, protein and blood gives
                           highest predictive value of negative culture (99.3) so conclude is
                           reliable for screening to avoid culture for all. (Sensitivity - 8.2 %,
                           specificity - 79 %, positive predictive value - 10.5 %)

Bachman           1993     Screening with urinalysis cost more than cultures for all
                           Reagent strips missed 50 % of ASB on initial exam

Tincello          1998     Reagent strips OK to use to determine need for culture
                           of symptomatic women. Not sensitive enough to screen for ASB

McNair            2000     High false negative rates with urinalysis & reagent strips
                           Urine cultures should be universally used to detect ASB
                           Chance of detecting ASB best in first trimester

"Urine culture remains the gold standard, and all pregnant women should have a
   screening culture during their early prenatal care."   Gilstrap 2001
          Proteinuria & Glycosuria Studies
Study     Year     Type of Study                 Focus         N

Watson    1990   Observational                 glycosuria     500

Gribble   1995   Retrospective chart review    glucosuria     2965

Gribble   1995   Retrospective chart review    proteinuria    3104

Hooper    1996   Retrospective chart review    glycosuria     600

Murray    2002   Prospective observational     proteinuria    913

Rhode     2006   Retrospective, non-inferiority proteinuria   1952
                   cohort design                glycosuria
                        Study Conclusions
Watson Routine screening for glycosuria does not appear to be clinically useful

Gribble 3rd trimester testing for glycosuria is not predictive of any clinically
                important pregnancy outcome
        Routine screening for glycosuria before the 3rd trimester may identify
                women at increased risk of GDM

Gribble   In low risk women with no signs of hypertensive disease, routine
          screening for proteinuria did not provide any clinically important
          information about pregnancy outcome

Hooper    Oral glucose diabetes screening and careful monitoring of blood
          pressure (and symptomatology) are better screens for GDM and
          preeclampsia than routine urinalysis

Murray After an initial screening urinalysis, routine urinalysis could be
       eliminated without adverse outcomes for women
    Research Setting & Population
Aurora Nurse Midwives Clinic, Aurora Colorado.

Started to provide care to medically underserved.

Approximately 1000 visits per month, mostly obstetric

Predominately Hispanic

Population considered high risk due to low socio-economic status

Only two bathrooms in the clinic
                     Study Objective

To determine if asymptomatic bacteriuria, elevated blood

pressure, and gestational diabetes are underdiagnosed if

routine prenatal urine screening is replaced with clinically

indicated testing.
Prior to August 2002
• Initial urinalysis, urine culture, BP
• One-hour 50-g load glucose challenge test at about 28 weeks
    gestation, (130 mg/dL threshold used for 3 hour GTT), at
    weeks gestation and a repeat at 28 weeks if risk factors
• Urine dipstick testing and BP at each follow-up visit

After August 15, 2002
• Same initial visit and GDM regimen
• Urine dipstick testing done only when established criteria*
   were present

Antepartum and intrapartum charts were reviewed after delivery
              Study Conclusion

A change to indicated urine reagent strip
testing does not result in under-diagnosis of
high blood pressure, urinary tract infection, or
gestational diabetes.
    Implications for Clinical Practice
  Changing long-standing clinical practices is

• Conduct a prospective, randomized trial and publish
  the results

• Have documentation articles available

• Make sure all involved are on-board, no saboteurs

• Give advance notice, educate everyone involved,
  including patients
            We are making a change
             we hope you will like!

Starting August 15, you will NOT need to give a
urine specimen every time you come to the clinic.
 We will ask for a urine specimen ONLY if you
have a problem. This change is based on scientific
   information that says urine testing of healthy
        women is not necessary every visit.
We are always trying to improve the way we give
  you the best care. This does not mean you are
                 getting less care.
    Compliance with established criteria is
         essential to patient safety!
Must get urine specimen whenever criteria are present

  No skipping, "just this one time"
  No repeating a blood pressure to avoid getting a urine specimen

Must document

  No reason for 18.1% of indicated tests
  No urine testing done on some subjects in each group
                 Not documented or not done?

Pay more attention to preeclampsia symptomatology since blood
  pressures may be labile
  Common Themes in Medico-legal Claims

• Assuming proteinuria is from contamination or

• Failing to appreciate the significance of patient
  complaints on the phone

Sibai, BM. Cutting the legal risks of hypertension in pregnancy. OBG
   Management. 2003.
Follow-up for Trace to 2 + Proteinuria

 • Repeat dipstick twice in the next month with
   a first morning specimen

 • If negative - transient proteinuria. No
   additional follow-up needed

 • If positive - persistent proteinuria. Needs
   24 hr. urine or urine protein/creatinine ratio
Indicated prenatal urine testing is

•     Safe
•     Patient-centered
•     Reduces cost of clinic operation
•     Improves clinic flow
•     Improves patient satisfaction.

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