During a scheduled mid-trimester visit at 20 weeks gestation, a 32-year-old multigravida r… — USMLE Step 2 CK

During a scheduled mid-trimester visit at $20$ weeks gestation, a $32$ -year-old multigravida reports feeling generally well, with only mild fatigue and occasional urinary frequency. Her blood pressure is $115/75$ mmHg and pulse is $82$ /min. Physical examination reveals a fundal height consistent with dates and normal fetal heart tones. Routine laboratory screening is performed with the following results:

Hemoglobin: $11.2$ g/dL
Leukocyte count: $12,500$ /mm $^3$
Serum creatinine: $1.1$ mg/dL
Alkaline phosphatase: $195$ U/L
Urinalysis: Trace glucose, negative for protein and nitrites

Which of the following laboratory findings in this patient is abnormal and warrants further diagnostic evaluation?

A
Hemoglobin of $11.2$ g/dL
B
Leukocyte count of $12,500$ /mm $^3$
Serum creatinine of $1.1$ mg/dLAnswer
D
Alkaline phosphatase of $195$ U/L
E
Trace glycosuria on urinalysis

Answer

The serum creatinine of

1.1

mg/dL is abnormal in pregnancy and requires further evaluation.

During normal pregnancy, maternal renal blood flow and glomerular filtration rate (GFR) increase by approximately

40\%

50\%

. This physiological hyperfiltration leads to increased clearance of urea and creatinine, resulting in a decrease in baseline serum levels. Normal serum creatinine in pregnancy typically ranges from

0.4

0.8

mg/dL. Therefore, a serum creatinine of

1.1

mg/dL, although within normal limits for a non-pregnant adult, is relatively elevated in this context and indicates underlying renal impairment that requires further diagnostic workup.

Step-by-Step Solution

Evaluate the hemoglobin level against pregnancy-specific reference ranges.

Hemoglobin of

11.2

g/dL is within the normal range for the second trimester (lower limit of normal is

10.5

g/dL).

Maternal plasma volume expansion exceeds red blood cell mass expansion, causing a physiological dilutional anemia.

Analyze the leukocyte count and alkaline phosphatase.

Both are physiologically elevated. WBC counts up to

15,000

/mm

^3

and elevated alkaline phosphatase (from placental production) are normal.

Recognizing pregnancy-induced baseline shifts prevents unnecessary workups for infection or hepatobiliary disease.

Assess the renal parameters (serum creatinine and urinalysis).

Trace glycosuria is normal due to increased filtered load. However, the serum creatinine of

1.1

mg/dL is abnormally high.

Pregnancy induces a

40\%

50\%

increase in Glomerular Filtration Rate (GFR), which should lower normal serum creatinine levels to

0.4

0.8

mg/dL. A level of

1.1

mg/dL suggests intrinsic renal dysfunction.

Key Concept

Physiologic renal adaptations in pregnancy include an increased GFR, leading to decreased baseline serum creatinine.

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