Which one of the following factors is most likely to invalidate the use of the Modification of Diet in Renal Disease (MDRD) equation to calculate a patients eGFR?
Correct Answer B: GFR tends to increase during pregnancy although the eGFR may not reflect this.
Chronic kidney disease: eGFR and classification:
Serum creatinine may not provide an accurate estimate of renal function due to differences in muscle. For this reason formulas were develop to help estimate the glomerular filtration rate (estimated GFR or eGFR). The most commonly used formula is the Modification of Diet in Renal Disease (MDRD) equation, which uses the following variables:
Factors which may affect the result:
CKD may be classified according to GFR:
*i.e. normal U&Es and no proteinuria.
Each one of the following is a cause of sterile pyuria, except:
Correct Answer B: Tubulo-interstitial nephritis may cause sterile pyuria but it is not seen with acute glomerulonephritis.
Sterile pyuria:
Causes:
Partially treated UTI
A 45-year-old presents to the Emergency Department with chest pain. An ECG shows anterior ST elevation and he is thrombolysed with alteplase. His chest pain settles and he is started on aspirin, atorvastatin, bisoprolol and ramipril. Four days later his blood results are as follows:
What is the most likely cause for the deterioration in renal function?
Correct Answer A: Flash pulmonary oedema, U&Es worse on ACE inhibitor, asymmetrical kidneys --> renal artery stenosis - do MR angiography.
There is likely underlying renal artery stenosis revealed by the addition of an ACE inhibitor. Risk factors such as hypertension and hyperlipidaemia which have contributed to the development of his ischaemic heart disease also put him at risk of renal vascular disease.
Renal vascular disease:
Renal vascular disease is most commonly due to atherosclerosis (> 95% of patients). It is associated with risk factors such as smoking and hypertension that cause atheroma elsewhere in the body. It may present as hypertension, chronic renal failure or 'flash' pulmonary oedema. In younger patients however fibromuscular dysplasia (FMD) needs to be considered. FMD is more common in young women and characteristically has a 'string of beads' appearance on angiography. Patients respond well to balloon angioplasty.
Investigation:
A 24-year-old man who has a sister with adult polycystic kidney disease (ADPKD) asks if he could be screened for the disease.
What is the most appropriate screening test?
Correct Answer D: Ultrasound is the screening test for adult polycystic kidney disease.
Genetic testing is still not routinely recommended for screening family members. Sensitivity for ADPKD1 is 99% for at-risk patients older than 20 years.
ADPKD:
Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of kidney disease, affecting 1 in 1,000 Caucasians. Two disease loci have been identified, PKD1 and PKD2, which code for polycystin-1 and polycystin-2 respectively.
The screening investigation for relatives is abdominal ultrasound: Ultrasound diagnostic criteria (in patients with positive family history):
Alport's syndrome is due to a defect in:
Correct Answer D: Alport's syndrome - type IV collagen defect.
Alport's syndrome:
Alport's syndrome is usually inherited in an X-linked dominant pattern*. It is due to a defect in the gene which codes for type IV collagen resulting in an abnormal glomerular-basement membrane (GBM). The disease is more in males with females rarely developing renal failure.
A favourite question is an Alport's patient with a failing renal transplant. This may be caused by the presence of anti-GBM antibodies leading to a Goodpasture's syndrome like picture.
Alport's syndrome usually presents in childhood. The following features may be seen:
*In around 85% of cases - 10-15% of cases are inherited in an autosomal recessive fashion with rare autosomal dominant variants existing.
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