Question

Mrs. Gardner is 48 years old woman diagnosed with breast cancer. She has been enrolled in a

clinical research trial testing the effectiveness of a new chemotherapeutic agent. After her

second dose of the agent, she complains of feeling light-headed when she gets out of bed

in the morning. Her blood pressure is found to fall from 135/80 to 105/70 when she goes from

a supine to a standing position (i.e., orthostatic hypotension). She also complains of frequent

urination and nocturia. Routine urinalysis reveals her urine contains large quantities of sodium.

However, her serum creatinine level is within normal limits at 1.0 mg/dl.

1. On the basis of the urinalysis results, her doctor suspects that the chemotherapeutic agent damaged her kidneys. Based on the information above, which portion of the nephron is likely damaged, the glomerulus, the proximal tubule, distal tubule, or collecting duct? Explain the reason for your choice.

2. Why do you think Mrs. Gardner has orthostatic hypotension? (Hint: think about the kidney’s role in maintaining blood pressure.}

Six Weeks Later

Mrs. Gardner’s renal issues, as described above, are successfully managed. She has

subsequently stated a different chemotherapeutic agent. However, 6 weeks later, she presents

to the emergency department with acute right flank pain and dark brown urine. She is admitted

to the observation unit. Laboratory analyses reveals:

Laboratory Values
	Admission	Hospitalization Day 1	Hospitalization Day 2	Hospitalization Day 3
Serum Creatinine	1.0 mg/dl	1.1	4.5	6.5
Serum BUN	20 mg/dl	24	40	60
Serum Cystatin C	elevated	elevated	elevated	elevated
GFR (estimated)	80 ml/min	60 ml/min	55 ml/min	50 ml/min
Urine Output	-------------	350 ml/day	340 ml/day	340 ml/day
Urinalysis	Protein +++
	Red Casts
	Hematuria

3. What is your assessment of Mrs. Gardner’s renal function? Based on the sequence of her laboratory values, discuss whether serum creatinine is a sensitive measure of changes in GFR? What is the added clinical value of serum Cystatin C?

4. What information does Mrs. Gardner’s urinalysis provide regarding the etiology of her renal impairment? Which portion of the nephron is likely damaged? Use the information above to support your answer.

Answer 1

1 - In this case, the proximal convoluted tubule of the nephron is damaged because 80% of the glomerular filtrate is reabsorbed here.

2 - I suspect Mrs.Garner has orthostatic hypotension because of hyponatremia and excessive fluid loss.

3 - From the assessment, it is clear that something is wrong with her renal function. Serum creatine is the most frequently measured analysis in clinical biochemistry as an indirect indicator of GFR. Serum creatine increases in renal failure correlating with a decrease in GFR forming a curvilinear relationship. Serum Cystatin c is useful to estimate GFR, especially to detect the reduction of GFR.

In this condition, the glomerular portion of the kidney will be damaged

4 - From her urine analysis it is clear that she has a condition called glomerulonephritis. This may be due to prolonged usage of chemotherapy medications.