The kidney is responsible for excreting nitrogenous substances in the urine, so an elevated BUN usually indicates that the kidney is not functioning appropriately. Urine Analysis (Urinalysis) - After the patient provides a urine specimen, it is sent to the lab for analysis using a variety of methods including urine dipstick testing and microscopic examination. Because the kidney is responsible for making urine, analyzing the urine directly can provide crucial data that can help the physician diagnose nephritic syndrome. Some findings on urinalysis that are consistent with nephritic syndrome include red blood cells (hematuria), red blood cell casts, proteinuria, and possibly white blood cells (pyuria).If nephritic syndrome is identified and diagnosed, then it is important for the physician to determine the underlying cause. To do this, he/she may order any of a large variety of relevant lab tests, some of which are included here:

Blood culture - This is the process where a sample of the patients blood is sent to the microbiology lab to attempt to isolate and grow any bacteria that may be circulating in the blood, in order to identify the pathogen. This is helpful if the physician suspects infection as the underlying cause of the nephritic syndrome. Antinuclear antibody (ANA) titer - ANA is commonly positive in patients who have an underlying autoimmune disease, so this test is useful if the physician suspects an underlying autoimmune disease (refer to the Causes section above for examples) as the cause of the presenting nephritic syndrome.
POLG encodes for the catalytic subunit pol γA, which is part of mitochondrial DNA polymerase.Other causes are mutations of thymidine phosphorylase (TyMP), succinate-CoA ligase, alpha sub unit (SUCLG1) and TWNK (also known as PEO1 and C10orf2). Diagnosis
MDDS is diagnosed based on systemic symptoms presenting in infants, followed by a clinical examination and laboratory tests (for example, high lactate levels are common) medical imaging, and usually is finally confirmed and formally identified by genetic testing. Classification
MDDS are a group of genetic disorders that share a common pathology — a lack of functioning DNA in mitochondria. There are generally four classes of MDDS:
a form that primarily affects muscle associated with mutations in the TK2 gene;
a form that primarily affects the brain and muscle associated with mutations in the genes SUCLA2, SUCLG1, or RRM2B;
a form that primarily affects the brain and the liver associated with mutations in DGUOK, MPV17, POLG, or TWNK (also called PEO1); and
a form that primarily affects the brain and the gastrointestinal tract associated with mutations in ECGF1 (also called TYMP). Treatment
There are no treatments for MDDS, but some of the symptoms can be managed. For survivors living with MDDS, there are drugs to control epilepsy, and physical therapy can help with muscle control. Liver transplants may benefit people with liver involvement. Prognosis
Myopathic form
The TK2 related myopathic form results in muscle weakness, rapidly progresses, leading to respiratory failure and death within a few years of onset. The most common cause of death is pulmonary infection. Only a few people have survived to late childhood and adolescence.